Agronomic Pest Control
A Study Guide for Commercial Applicators
A supplement to be used with Bulletin 827
Feb 2005 - Ohio Department of Agriculture – Pesticide Regulation
This manual contains some of the information needed to become a certified commercial applicator in Category
2a Agronomic Pest control. This study guide is intended for use in combination with the Applying Pesticides
Correctly Core Training Manual (Extension Bulletin 825) and also the Corn, Soybean, Wheat and Alfalfa Field
Guide (Extension Bulletin 827). These bulletins are available through the Ohio Department of Agriculture –
Pesticide Regulation – Certification Section.
Author: Diana Roll
Editors: Dr. William Pound
The Ohio Department of Agriculture would like to thank the following institutions for their contributions to this
The University of Nebraska Lincoln
The Ohio State University
Table of Contents
Chapter 1 Laws for Ohio 4
Chapter 2 Integrated Pest Management 10
LAWS AND REGULATIONS
1. Learn what state and federal laws govern agronomic crop pesticide applications
2. Definition of category
3. The State Plan for Ohio
4. Standards of competency
5. Pesticide license information
STATE AND FEDERAL LAWS
The Pesticide Applicator Core Training Manual details federal and state laws that govern the handling
and use of pesticides. Review the core manual to understand how laws and regulations affect pesticide
practices and use. These laws include federal laws such as the Federal Insecticide, Fungicide, and
Rodenticide Act (FIFRA), the Occupational Safety and Health Act (OSHA), the Endangered Species
Act, and the Federal Migratory Bird Treaty Act. Pesticide technicians should keep up-to-date copies of
the laws and review their contents periodically. Copies of these laws can be obtained from the Ohio
Department of Agriculture.
This is the basic federal law administered by the Environmental Protection Agency (EPA) that regulates
pesticides (their use, handling, storage, transportation, sale, disposal, etc.). The Ohio Department of
Agriculture (ODA) has a cooperative agreement with the EPA to enforce some provisions of FIFRA in
Ohio. Some of the provisions of FIFRA are that the EPA must register all pesticides before they can be
sold or used. The pesticides must be classified as either "general use" or "restricted use.” General use
pesticides are those that can be purchased without restriction. Restricted use pesticides are those that can
be used only by or under the direct supervision of a certified applicator. FIFRA also stipulates that
persons who misuse pesticides (in a way that is "inconsistent with the pesticide labeling") are subject to
The U.S. Department of Labor (DOL) administers OSHA. OSHA governs the record-keeping and
reporting requirements of all work-related deaths, injuries, and illnesses of businesses with 10 or more
Endangered Species Act
This act requires the U.S. EPA to ensure that endangered or threatened plant and animal species are
protected from pesticides. This act requires each pesticide label to limit its use in areas where these
species could be harmed. Category 2a applicators must consider the possibility that the pesticides they
apply may affect endangered or threatened species. The Ohio Department of Natural Resources (ODNR)
Wildlife and Fisheries Management divisions maintain the federal and state endangered or threatened
species lists. Ohio applicators that want to be sure they are complying with the act must take the
initiative and consult with the ODNR to be sure that there are no endangered or threatened species in
their area. One of the goals of pest management is to protect off-target plants and animals from
pesticides, whether they are endangered or not.
THE STATE LAW
The Pesticide Law
The Ohio Pesticide Law is the law that governs the pesticide applications in the state of Ohio. The Ohio
Department of Agriculture is the state agency that regulates this law and the pesticide applicators that
are licensed by the state. If you have any questions or concerns, please contact the Ohio Department of
Agriculture, Pesticide Regulation Section at 614-728-6987 OR TOLL FREE AT 1-800-282-1955.
DEFINITION OF CATEGORY
The definition for agriculture pest control as stated in the law is as follows: Category 2a is "Agriculture
Pest Control" which means the application of pesticides to any agronomic and horticultural crops, or to
soils being prepared for the production of such crops, for the control of pests other than weeds and
vertebrates. The subcategory an “Agronomic Pest Control” means the application of pesticides to
agronomic crops for the control of pests other than weeds and vertebrates.
THE STATE PLAN FOR OHIO
The State Lead Agency
The state lead agency for the plan is the Ohio Department of Agriculture. The Governor assigned the
responsibility of this plan to the Division of Plant Industry on March 12, 1973.
The State Plan Document
The plan is the document by which the Ohio Department of Agriculture, Pesticide Regulation Section
and The Ohio State University Extension share the responsibilities for the certification and training of
the Ohio pesticide commercial and private applicators. The Ohio Department of Agriculture is
responsible for the testing and licensing of pesticide applicators. The Ohio State University Extension is
responsible for the continuing education credits for those applicators that wish to re-certify and not re-
The plan sets forth the standards by which the Ohio Department of Agriculture and The Ohio State
University Extension develop study materials, pesticide exams and pesticide training. These standards
are called “Standards of Competency.”
Standards of Competency
Commercial applicators are required to demonstrate their knowledge and understanding of the handling
and use of pesticides by means of written, closed book examinations; based on the standards of
competency set forth in 40 Federal Code of Regulations (CFR) 171.4. Standards are set forth for the
Core exam and for all the categories. The additional “Standards of Supervision” of non-certified
applicators must be met, such as availability related to the hazard of the situation. Also needed are
instructions and guidance when presence of a supervisor is not required.
Commercial applicators shall demonstrate practical knowledge of the principles and practices of
pest control and safe use of pesticides
A comprehension of labeling format and terminology together with an understanding of
permitted uses, classification, associated warnings, precautions and other restrictions, such as
Safety factors related to handling, storage and disposal of pesticides, particularly those factors
pertaining to the prevention of personal injury through accidents, misuse, symptoms of pesticide
poisoning and first-aid treatment
Adverse environmental effects, such as water or soil pollution and injury to non-target organisms
The recognition of common types of pests, their damage symptoms, basic developmental stages
and optimum periods of pesticide susceptibility
Types of formulations of pesticides (both chemical and functional), their modes of action,
persistence and compatibility with various other compounds
Application techniques for greatest effectiveness with minimal adverse side effects
Appropriate state or federal laws pertaining to the production, distribution, sale or use of
pesticides and to the supervision of non-certified applicators
Potential of contaminating wells, ground water and surface water by pesticides
Areas in the state where endangered or threatened plants and animal species are to be protected
Agriculture Pest Control “2” Subcategory “a” Agronomic Pest Control; Commercial applicators
shall demonstrate a practical knowledge of:
The more significant insect and disease pests affecting agronomic field crops
Effective pesticides and their relative persistence
Equipment and application techniques
Factors relating to safety such as pre-harvest and reentry intervals, potential environmental
pollution or contamination and residues
Other pertinent information necessary for safe and adequate application of pesticides
PESTICIDE LICENSE INFORMATION
The application and fee are only valid for the licensing year noted on the application and cannot be
extended to the next licensing year once it is submitted. If all requirements are not met within the
license year listed on the application, the application and fee are voided and the fee is non refundable.
License fees cannot be transferred from one company to another. When a first time applicant submits
the application and fee, study material will be sent to assist in preparation for the examinations.
Categories are listed on the application.
Examination requirements are: the General-Core examination which covers the law, regulations, safety,
disposal and related topics, and an examination for each category in which you need to be certified and
licensed. The categorical examinations are specific to what area you will be applying the insecticide,
herbicide, fungicide, etc. All examinations consist of multiple choice and some true/false questions on
the older exams. The exams are not open book exams. Exam results are mailed two-three weeks after
the test date; they are not given over the phone. If you fail the exams, you must wait at least five days to
retest. If you need to retest there is no additional fee required. Exams are only valid for one year from
the date you pass the exam. Within that year if you do not meet the other qualifications for a license to
be issued, the exams expire and you will need to retest. There is a Pesticide Applicator New School for
new applicants conducted by The Ohio State University that is held every year in late February or early
March. Their web site is: http://pested.osu.edu this site also offers other licensing information: test sites,
recertification sites and study material. Please call the Pesticide Regulation Section at (614) 728-6987 or
1-800-282-1955 to schedule your appointment to take the exams or register on line at
http://pested.osu.edu. The application is only valid for the licensing year in which you have applied.
(The year is listed on the application.) If you do not meet requirements within the year that you have
applied, then a new application and fee will be required, and no refund is given. Ohio Dept. of
Agriculture web site: www.ohioagriculture.gov - look under “Pesticides.”
Commercial Renewal and Recertification Information
Once you have passed the applicable exams for the license and a license has been issued, you are
certified for three years. The license must be renewed continuously every year in order to keep the
three-year certification valid. You need to renew the license every year (at the end of September), which
consists of submitting a renewal application and fee. You need to recertify every three years (the
recertification due date is printed on your license) by retesting or attending recertification programs.
Your recertification is based on the first year you obtained your license, which is based on the license
year you passed exams and met all other requirements. Once you have been issued a license, you may
begin obtaining your recertification credits at any time during the three-year recertification cycle. You
must obtain the following requirements for recertification: TOTAL MINIMUM OF FIVE HOURS
OF TRAINING CONSISTING OF 1 HOUR OF CORE TRAINING AND ½ HOUR IN EACH
CATEGORY YOU ARE LICENSED – HOWEVER, IT MUST BE A TOTAL MINIMUM OF
FIVE HOURS. If you have met your category requirements you must still make sure you meet the time
requirement by attending approved classes whether or not they are in your licensed category.
If you do not meet the recertification requirements of 1-hour minimum in Core, at least ½ hour in your
licensed category or categories with a total minimum time of 5 hours before the recertification
expiration date listed on your license, then you must retest.
1. FIFRA is the state law that governs pesticide applicators in Ohio:
B. False *
2. The Ohio Pesticide Law is the document that sets forth the standards of competency for pesticide
B. False *
3. The general standards are the standards that set forth the competency for the specific categories:
B. False *
INTEGRATED PEST MANAGEMENT
1. Learn about Field Scouting
2. Economic Thresholds and Loss Levels
3. Plant Pests
4. Growth Stages
INTRODUCTION AND FUNDAMENTAL CONCEPTS
Integrated Pest Management (IPM) had an intimate association with the production of field crops,
beginning long before its more formal introduction by the Extension Service during the early 1970s.
Farmers have in many cases unwittingly practiced sound pest management schemes for hundreds of
years on this continent and for a much longer period in the Old World. Strategies such as multiple crop
rotations, early harvesting, strip cropping, mechanical cultivation, trap cropping, and manipulating
planting dates are not new pest management concepts and have been relied upon by farmers for
The first organized and sponsored Extension Service-IPM efforts started in 1970's with a pilot scouting
program. A major emphasis was placed upon scouting and the use of thresholds for insects in corn. The
procedures followed by entomologists involved in this early IPM program were:
1. contacting farmers;
2. determining agronomic and cropping history of fields;
3. estimating plant stand;
4. determining the percentage of whorl feeding by European corn borers;
5. estimating corn rootworm and corn leaf aphid densities; and
6. recording the presence of beneficial insects.
During the last twenty years, producers and the general public have both become much more aware of
the important and expanded role that IPM programs must continue to play in the efficient production of
food and fiber, while enhancing the integrity of the environment.
In natural settings such as forests, lakes, or undisturbed fields, populations of organisms generally exist
within a self-regulating system. A system that reaches a point of equilibrium over time is referred to as
an ecosystem. This balance of plant and animal life is more difficult to achieve within a field devoted to
the production of crops. Agricultural ecosystems, popularly known as agro ecosystems, contain far less
diversity of both animal and plant species than occurs in natural ecosystems. Because of this lack of
diversity of organisms and the frequent people-imposed disturbances placed upon agro ecosystems such
as tillage operations, mowing, or the use of pesticides, certain populations of organisms may increase in
numbers and threaten the profitable production of a given crop. Populations of organisms whose
densities reach levels that begin to compete with the desired production of food and fiber are referred to
as pests. As used in this manual, the term pest refers to any organism that is injurious to cultivated
crops. Although pest is often used interchangeably with insect, pests of field crops include insects,
weeds, nematodes, plant diseases, and rodents. Control measures for all pests should be integrated into a
crop management system that ensures economically viable crop production and environmental
stewardship. Integrated pest management has been popularly defined as the intelligent selection and use
of pest control practices that ensure favorable economic, ecological, and sociological consequences.
PESTICIDE USE ON FIELD CROPS
Pesticide use patterns are similar throughout the Corn Belt in the north central region of the United
States. The percentage of corn and soybean acres treated with pesticides remains very high. The use of
herbicides and insecticides accounts for the largest share of pesticide applications made each season.
The lack of crop rotation continues to be the main contributing factor responsible for the heavy reliance
on soil insecticides by corn producers across much of the Midwest. Several million acres of continuous
corn (corn not rotated with other crops) are grown each year in Ohio. At planting, 80 - 90 percent of
these acres are treated with a soil insecticide aimed primarily at the corn rootworm complex. Recent
research conducted in several corn-producing states indicates that more continuous corn acres are being
treated each spring than are probably necessary. Research has also shown that only about half of the
treated acreage in some years actually warranted a treatment. However, because many of these acres are
not scouted the previous season, producers have little or no information upon which to base their
decision to use a soil insecticide during spring planting. Thus, many continuous corn acres are treated
prophylactically (no scouting input before treatment) each season. In some cases for individual
producers, certain continuous cornfields have received annual applications of a soil insecticide for
fifteen years or more although there is little or no idea of the corn rootworm population.
The sound practice of growing corn in rotation with soybeans occurs on many Ohio acres and largely
eliminates the possibility of serious corn rootworm damage; however, some of these "first-year" corn
acres are still treated annually with a soil insecticide. The percentage of total corn acres treated with a
soil insecticide has steadily decreased from 1978 to present. This reduction has occurred primarily
because more and more producers are reluctant to treat first-year corn acres with a soil insecticide.
Instead, they monitor fields for insect pests such as black cutworms and rely on the use of rescue
treatments if necessary.
In Ohio over 90 percent of the corn and soybean acreage are treated with herbicides. Although the
acreage treated remains very high, total pounds of herbicide active ingredients applied in the state
decreased significantly on corn and soybeans during the 1980's. This reduction has been achieved
largely due to the use of newer herbicides, which provide weed control at lower rates, not because of a
fundamental shift in how producers manage weed populations.
In most parts of the country, resistance of weeds to herbicides is not currently causing problems for the
vast majority of producers. On a worldwide scale, however, reports of herbicide-resistant weeds have
increased during the last decade. Therefore, sound weed-management strategies should be used, and the
following exploitive practices should be avoided: failure to rotate crops; over-reliance and frequent use
of a single, highly effective herbicide; overuse of tank mixtures of herbicides with similar modes of
action; and lack of integration of chemical and non-chemical weed management strategies.
SCOUTING FIELD CROPS FOR PESTS
One of the keys to a successful IPM program is regular monitoring of field-crop conditions and pest
infestations. A scouting trip through a field reveals which pests are present, what stage of growth each
pest and the crop are in, whether the pests are parasitized or diseased, whether a pest infestation is
increasing or decreasing, and the condition of the crop. This information can be used to determine
whether a control measure may be needed. It has been estimated that about 60 percent of the corn and
soybean acres are scouted. A very small percentage of the corn and soybean acres are scouted by
professional consultants. Although the percentage of field crop acres scouted has increased steadily, the
fact that a large percentage of the corn and soybean acres are not monitored warrants vigorous support
of expanded IPM educational programs.
A scouting program requires accurately written records of the field location, current field conditions, a
history of previous pest infestations and pesticide use, and a map locating present pest infestations.
These records will enable the grower to keep track of each field and anticipate or diagnose unusual crop
Insect pests can be monitored in several ways. Usually, the insects are counted or the amount of crop
damage is estimated. Counts of insects are commonly expressed as number per plant, number per row
foot, number per sweep, or number per unit area (square foot or acre). Estimated crop damage is usually
expressed as a percentage. Methods of scouting for insects include collecting insects with a sweep net,
shaking the crop foliage and counting dislodged insects, counting insects on plants, and using traps.
Plants should also be examined for symptoms of disease, and, if infected plants are found, the severity of
the disease should be determined. Soil samples are required for estimating densities of nematodes, and,
in some instances, plants may have to be analyzed at a diagnostic laboratory.
Early season weed scouting should be conducted within two weeks after crop emergence to evaluate the
performance of herbicides and determine whether rotary hoeing, cultivation, or postemergence
herbicides are needed. A weed map should be made for each field to indicate the location of various
species of weeds. Over time, these maps may reveal a shift in the composition of weed species within
specific locations of a field.
Certain basic principles of crop monitoring apply to most scouting programs. Samples should be taken
from representative areas of the field. The sampling sites should be evenly distributed over the field, and
plants should be sampled randomly unless certain field characteristics suggest an uneven distribution of
pests. Avoid border rows and field edges unless there are specific reasons for scouting these areas. Scout
at least once a week, although some fields may require monitoring more frequently if insect densities
begin to increase rapidly.
ECONOMIC THRESHOLDS AND LOSS LEVELS
The most familiar feature of field-crop IPM programs is scouting fields for pests and basing treatment
decisions on economic thresholds, popularly referred to as "action thresholds." The economic threshold
(ET) is that pest density at which some control should be exerted to prevent a pest population from
increasing further and causing an economic loss. Examples of economic thresholds for some insect pests
in various crops include:
1. black cutworms in corn: "Apply a postemergence rescue treatment when 3 percent or more of the
plants are cut and larvae are still present,"
2. bean leaf beetles in soybeans: "When defoliation reaches 30 percent (before bloom) and there are
5 or more beetles per foot of row," and
3. potato leafhoppers in alfalfa: "Treatments are recommended when a certain number of potato
leafhoppers are collected per sweep at a given plant height (e.g., 0.2 leafhoppers per sweep when
plants are 0 to 3 inches tall)."
For plant diseases, damage thresholds are used to help make treatment decisions. Because pathogens
are too small to be seen without a microscope, counting is not generally practical; therefore, an estimate
is made of the amount of damage caused by a pathogen. The damage threshold is the maximum damage
a crop can sustain without yield loss. Damage thresholds have been determined for many plant diseases.
Examples for using these thresholds include: counting diseased leaf petioles for soybean pod and stem
blight; estimating the percent infection of the flag leaf by rust pustules, or other fungal foliar blights, in
wheat; determining the density and kinds of nematode populations in a soil sample; and estimating the
percentage of whole plant infection caused by fungal leaf blights in corn.
An economic threshold for weeds is that density of weeds at which control is economically justified
because of potential for yield reduction, quality loss, or harvesting difficulties. Densities of weeds that
lower yields by more than 10 percent are generally above the economic threshold.
Another level of pests frequently referred to in pest-management programs is the economic injury level
(EIL): the lowest pest density at which economic damage occurs. Another way of interpreting the EIL is
to think of it as that level where the cost of the control measure is equal to the loss likely to be inflicted
by the pest.
It is worthwhile to keep in mind that the ET and EIL are mathematically determined densities of pests
and based upon a detailed knowledge of pest ecology (the potential value of the harvested crop and the
cost of pest control practices) as well as economics. Economic thresholds may vary with the field, crop
variety, and stage of crop growth and decrease as the value of the crop increases, but they increase as the
cost of control increases.
Long-term population levels of organisms, referred to as the general equilibrium position, (GEP) are
generally unaffected by periodic pest control activities. Population densities of pests fluctuate around the
GEP, and what triggers periodic outbreaks of many pests is poorly understood.
Numerous examples of pesticide reductions have been achieved because of improved pest-monitoring
techniques and growing acceptance of the ET and EIL concept. However, thresholds that incorporate
environmental costs are not being popularly developed or used. Even though ETs and EILs have helped
reduce pesticide overuse, they inherently do not reflect any of the potential environmental hazards
associated with a pesticide treatment. Environmental hazards associated with pesticide use are often
referred to as unwanted externalities and include reduced densities of beneficial insects such as
predators and parasitoids; pesticide residues on food products; pesticide detections in surface and
groundwater supplies; and wildlife kills. Before environmental thresholds can be used on a large-scale
basis, monetary values will need to be attached to potential hazards to natural resources because of a
For many pest control situations, it is difficult to assess the potential economic benefit and
environmental hazards associated with a pesticide application. Clearly, the sustained and prophylactic
use of pesticides is in direct opposition to a sound pest-management philosophy. However, for most
pest-management scenarios, treatment decisions are not always clear. In order to determine whether a
pesticide application is warranted, many individuals, perhaps unknowingly, assess the costs as well as
the benefits of a treatment. This step is often referred to as determining the cost/benefit ratio. In
attempting to estimate the cost/benefit ratio a few points are worth considering. First, pesticides rarely
increase yield; rather, the use of a pesticide may prevent a loss of yield due to pest activity. Second, the
benefits of some pest control practices in agricultural situations are not known. If you find this hard to
believe, ask yourself: how many producers leave check strips (no pesticide used) in their fields and
measure yield from treated and untreated areas?
After determining the potential benefits of a pesticide application, one also should begin to identify
some risks that may be linked to the use of a given product. An analysis of the benefits and risks of a
pesticide treatment leads to the formulation of the benefit/risk ratio. What are the risks to the pesticide
applicator's personal health and safety? What are the broader risks to society and the environment?
These questions are often difficult, if not impossible, to answer satisfactorily. However, they must be
raised continually and answers sought.
Insects that inhabit cultivated crops and rarely if ever reach densities sufficient to cause economic injury
are referred to as nonpests. Common examples of these insects in Ohio field crops include pea aphids
on alfalfa, yellow woollybear on corn, and painted lady on soybeans. Other field-crop insects reach
damaging densities only as the result of unusual environmental conditions or frequent nonselective use
of an insecticide. These insects are referred to as occasional pests. Most of the insect pests in Ohio field
crops are occasional pests, for example, green cloverworm and Twospotted spider mite (not an insect)
on soybeans, corn leaf aphid and black cutworm on corn, and grasshoppers and spittlebug on alfalfa.
Some insects are able to inflict economic losses on a frequent basis because their established economic
injury level is just above the general equilibrium position for their population. These insects are referred
to as perennial pests. In an effort to limit the economic losses they cause, periodic control measures
must be used when their density increases. Examples of perennial insect pests in field crops are not
common; however, some entomologists consider corn rootworms to be a perennial pest in continuous
corn. Some insects are referred to as severe pests and are characterized by causing economic injury
levels below the general equilibrium position. A familiar example of this type of pest that continually
plagues sweet-corn producers is the corn earworm. In an effort to produce a marketable crop, sweet-corn
producers must monitor the corn earworm moth flight and be prepared to make timely and repeated
Management of plant disease problems in field crops relies on several factors. The first is a working
knowledge of what are common and what unusual diseases in your region are. Second is the proper
identification of the disease based on signs, symptoms, and field distribution patterns, and observation of
the severity of the disease must then be done. Finally, familiarity with the damage threshold for a given
disease is necessary so management decisions can be made before the economic injury level is reached.
Plant diseases result from four interacting conditions:
1. a susceptible host;
2. an environment favorable for disease development;
3. a disease-causing agent; and
4. adequate time for disease development.
If any one of these conditions is not met, an economic loss probably will not occur. Some endemic
diseases are present every year and generally do not cause significant damage. If all conditions favor the
development of endemic diseases, however, economic losses may occur. When a disease becomes
severe it is an epidemic disease, and control measures are usually necessary. Epidemic diseases vary
from year to year depending upon the weather, crops grown, and crop varieties or hybrids.
Plant diseases can be divided into two broad categories: infectious and noninfectious. Infectious plant
diseases are caused by a wide range of pathogens such as fungi, bacteria, nematodes, viruses, and
mycoplasmalike organisms, or by parasitic plants such as dodder. These pathogens multiply within the
host plant and can be transmitted from plant to plant. They may either invade the entire plant (systemic
infection) or only affect certain plant parts (localized infection).
Noninfectious diseases are caused by abiotic (nonliving) agents. These agents cannot multiply within the
host and cannot be transmitted from plant to plant. They are generally the result of unfavorable
environmental or chemical conditions such as unfavorable temperatures, soil compaction, drought, or
flooding, nutrient imbalances, air pollution, or chemical excesses and misapplication.
Most plants produce characteristic symptoms in response to infectious plant disease that greatly aid in
diagnosing the cause of the disease. Symptoms are the plant's expression of disease. Some symptoms are
easily seen such as wilts, lesions, yellowing, abnormal growth, mosaics, and root rots, whereas others,
such as shriveled seed or reduced seed quality, may not be noticed until the crop is harvested.
Signs of infectious plant diseases are the evidence of the actual pathogen itself. Some signs of a
pathogen are visible with an unaided eye, for example, mushrooms, exterior fungal mats (mycelium),
large sclerotia, or fungal pustules. Others, such as asexual spores (conidia), internal mycelium,
perithecia, small sclerotia, bacterial ooze, or virus particles require the use of a hand lens or a
microscope to be visible. Plants affected by noninfectious diseases also produce characteristic
symptoms. For instance, air pollution can cause leaf bronzing or scorching. However, no signs will be
present because noninfectious disease is not caused by plant pathogens. This often makes diagnosis
somewhat more difficult.
Observation of field distribution is also important for diagnosis. The most common distribution for
field-crop disease is a random pattern. A disease distribution moving in from the edges of the field is
often indicative of an insect-vectored disease. Another common pattern is disease associated with areas
of high stress, such as low or compacted areas.
The major corn diseases can be grouped into four categories: leaf blights, stalk rots, ear rots, and viral
Leaf Blights: A number of leaf-blight diseases occur on corn. The most common are gray leaf spot,
Stewart's bacterial leaf blight, and northern corn leaf blight. These diseases can be found in almost any
field, depending on the year and susceptibility of the hybrid planted. Some leaf-blight diseases are most
often found associated with continuous corn, especially in reduced-tillage, continuous corn fields. These
are anthracnose, gray leaf spot, eyespot, and northern leaf spot.
All leaf blight diseases cause loss of green leaf tissue, resulting in fewer kernels and lightweight grain.
Plants may be predisposed to stalk-rot diseases when leaf damage is severe. The amount of yield loss is
usually related to the time when the plant's upper leaves become infected. The most severe yield loss
occurs when the upper leaves, the ear leaf, and those above the ear, become infected at or soon after
tasseling. Yield losses will be minimal if disease does not occur on these leaves until six to eight weeks
Leaf blight diseases are most effectively controlled by selecting hybrids with genetic resistance. Contact
your seed dealer for information on hybrids with resistance to gray leaf spot, Stewart's bacterial leaf
blight and other leaf diseases important in your area. A one-to two-year rotation away from corn and
destruction of old corn residues by tillage may be helpful if susceptible hybrids must be grown.
Fungicides are also available for control of leaf diseases, but are economically viable only under severe
Stalk Rot: Stalk rots are the most important and common diseases of corn. Annual losses are estimated
at 5 to 10 percent. There are several stalk-rot diseases, but Gibberella stalk rot and anthracnose stalk rot
currently are the most prevalent. Both are fungal diseases that result in premature ripening, chaffy ears,
and lodging of plants before harvest. The interior of the stalk becomes rotted, tissues break down, and
the stalk is easily broken. Anthracnose stalk rot is usually associated with continuous corn and is
recognized by the blackening of the outer surface of the stalk late in the season. Stalks with Gibberella
stalk rot can be found in nearly any field. Affected stalks often have pink to reddish discolored internal
tissues. Control of stalk rot diseases is based on reducing plant stress from factors such as lack of
moisture, leaf diseases, insect injury, and nutritional stress. To reduce the affects of stalk rot diseases,
follow as many of the following practices as possible:
1. Select hybrids with good standability and resistance to leaf blight diseases.
2. Adjust soil fertility to recommendations based on a soil test. Avoid excessive rates of nitrogen in
relation to potassium.
3. Follow a one- to three-year rotation away from corn. Soybeans, forage legumes, and small grains
are acceptable in the rotation. The longer the rotation away from corn the better.
4. Plant at populations recommended for the hybrid grown. Over planting leads to increased
moisture, light and nutrient competition, and more plant stress.
5. Harvest fields with the greatest level of rotted stalks first to avoid lost ears on lodged plants.
6. Control insects, particularly root worms and stalk borer. Insects cause injuries to plant roots and
stalks permitting stalk rot fungi to enter the plant. See Ohio State University Extension Bulletin
545 Insect Pests of Field Crops for insect control recommendations.
Ear Rot: Gibberella, Fusarium, and Diplodia ear rot diseases occur in Ohio, but Gibberella ear rot is the
most important. The Gibberella ear rot fungus is the same fungus that causes Gibberella stalk-rot
disease. Gibberella enters from the silk end of the ear when cool, wet weather persists for several weeks
through late silking of the crop. The occurrence of a whitish to pinkish mold on the ear tip is diagnostic,
but extensive mold growth may not occur. On shelled grain, the symptoms may be seen as a pinkish
coloration in some of the kernels. Even though extensive rotting does not always occur, the disease is
serious because the fungus frequently produces toxins that makes the corn unfit for feeding. Hogs are
particularly sensitive to the toxins produced in moldy grain and may refuse to eat it even when hungry.
If hogs refuse to eat grain, have a mycotoxin analysis run to determine the kinds and levels of toxin
present. Some corn hybrids are less susceptible than others to Gibberella ear rot. Ears with tight husks
which mature in an upright position often have more ear rot than those maturing in a declined position.
Diplodia ear rot appears to be more common in continuous corn under reduced tillage. Ears affected by
Diplodia are covered with a thick mat of white fungal growth. Fusarium ear rot is common, but only
individual kernels are affected on ears. Plant hybrids known to be less susceptible to these ear diseases.
Grain with evidence of ear or kernel rot should be dried to 14 percent moisture before storage and
maintained at this level until used. Feeding less than 5 percent moldy kernels may prevent feeding
problems, but grain should be tested for mycotoxin levels prior to feeding to avoid any problems. For
more information on mycotoxins, refer to Ohio State University Extension Bulletin 735 Moldy Grains,
Mycotoxins, and Feeding Problems or contact Ohio State's Plant and Pest Diagnostic Clinic.
Virus Diseases: Maize dwarf mosaic and maize chlorotic dwarf are potentially destructive diseases
where johnsongrass is established. The two viruses that cause these diseases are able to survive in this
perennial weed grass. Aphids and leafhoppers feeding on johnsongrass in the spring pick up the virus
and inoculate nearby corn. Control is achieved by planting resistant or tolerant hybrids. Efforts also
should be made to eradicate johnsongrass.
Management Practices for Corn Diseases
1. Select corn hybrids with resistance to northern corn leaf blight and Stewart's bacterial leaf blight.
Some hybrids are now available with moderate levels of resistance to gray leaf spot. In areas
infested with johnsongrass, corn hybrids with resistance to virus diseases also may be necessary.
Corn hybrids with resistance to stalk rot, ear rot, and other leaf diseases also are available.
Contact your seed dealer for details.
2. Plant only high-quality seed with a high germination percentage. Plant in a well-prepared seed
bed when the soil temperature is 55 degrees F or above and moisture level is sufficient for rapid
germination and growth of seedlings. Most seed corn is treated with a fungicide by the seed
producer to control seedling diseases. Seed treatment is particularly important when planted
early in cool, wet soils.
3. Cultural practices such as crop rotation and tillage are important disease-control methods. Corn
should be rotated with legume and/or small grain crops. If no tillage is used, a two-year period
away from corn is recommended, but a one-year rotation away from corn may be sufficient if
residues are destroyed by tillage.
4. To ensure good growth and acceptable yields, provide adequate fertility based on a soil test. Plan
a balanced fertility program, avoiding excessive rates of nitrogen or other nutrients. Replace
nutrient levels as required by amounts harvested in plant products.
5. Control insects and weeds. See Ohio State University Extension Bulletins 545, Insect Pests of
Field Crops and 789, Weed Control for Ohio Field Crops for specific control methods.
6. Harvest promptly when corn matures to 23 percent moisture for shelled and 25 percent moisture
for ear corn. For long-term storage, ear corn should be 20 percent moisture or less, and shelled
corn should be 14 percent moisture.
The major soybean diseases can be classified as root rots, stem rots, leaf blights, and seed diseases.
Root Rots: Several root and lower-stem rot diseases are frequently encountered. These diseases are
caused by fungi that live in the soil and parasitize the lower portion of the soybean plant. The two most
common are Phytophthora root rot and Rhizoctonia root rot. Phytophthora root rot is the most
destructive. Thousands of acres of soybeans are destroyed by this disease each year. The Phytophthora
fungus attacks plants at any stage of growth, from germinating seedlings through mature plants. Infected
plants generally wilt and die soon after infection or are stunted. Phytophthora root rot occurs most
frequently in heavy soils with poor drainage or in years with high rainfall. Fungal populations are
comprised of a number of races that attack varieties with different genes for resistance. Rhizoctonia root
rot is generally more prevalent in years when weather conditions are dry in early spring and then turn
wet; however the disease can occur under other conditions, as well. Rhizoctonia attacks the base of the
plant at the soil line causing reddish-brown cankers on the lower stem. Charcoal rot has occurred in
Ohio in years with high temperatures during pod-filling. Temperatures at 85 to 95 degrees F for
extended periods favors disease development as does drought stress. Symptoms include stunting,
yellowing of leaves, discolored root tissues, and premature death. Diagnosis of charcoal rot is based on
characteristic black zoning or charcoal-colored speckling within root tissues. There are no adequate
management methods for Rhizoctonia root rot and no resistant varieties are available for charcoal rot.
Adequate fertility, a three-year crop rotation including small grains or corn may help in reducing losses.
Phytophthora root rot can be controlled with resistant soybean varieties. However, a number of different
races occur, so previously resistant varieties may be susceptible to new races that develop within fields.
Varieties with a high level of partial resistance are also available. These varieties are susceptible to
infection, but do not have the excessive yield loss associated with susceptible varieties. A listing of
varieties with specific Rps resistance genes to the prevalent races of Phytophthora and ratings for the
level of partial resistance to the disease are provided in the current edition of Ohio Soybean Performance
Trials, Horticulture & Crop Science, Series 212, available from your local county Extension office.
Performance of resistant and partial resistant varieties can be improved by treating seed with fungicides
that control Phytophthora. Losses also can be reduced by using some form of tillage and providing
adequate subsoil and surface drainage to problem fields.
Stem Rots: The symptoms of most stem rots develop two to three weeks prior to maturity and often are
misdiagnosed as early maturing beans. Cool, wet weather conditions in midsummer favor development
of Sclerotinia white mold, brown stem rot, and Diaporthe stem rot which are all found in Ohio. Hot, dry
summer conditions promote the development of charcoal rot. Sclerotinia white mold is the most
common of the stem rot diseases and has been increasing in incidence in Ohio. This disease has a
characteristic fluffy white mold growth that develops on the nodes and stems. The white mold continues
to grow and causes a girdling lesion on the stem. The leaves wilt and turn brown, affected plants die, but
remain erect in the field. These dead plants with wilted leaves can be spotted in fields during mid- to late
August and can be confused with brown stem rot. Black, hard sclerotia (resistant fungal bodies) develop
both inside and outside the stems and within the pods. These sclerotia are harvested with the beans and
can be collected with seed by combines, returned back to the soil with the debris, or carried from field to
field on harvesting equipment. Management of this disease is first dependent upon preventing
introduction into a field. Plant only well-cleaned seed and treat seed with a fungicide effective against
Sclerotinia. Some varieties do appear to be less susceptible to this pathogen by having less disease by
the end of the season. It will be difficult to reduce the level of Sclerotinia in fields with high disease
severities, but long crop rotations with corn, wheat, and/or alfalfa and selecting varieties that are less
susceptible should improve the productivity of affected fields.
Leaf Diseases: Several leaf diseases of soybean are common every year, but they seldom destroy
enough leaf tissue to reduce yields. One of these diseases, Septoria brown spot, usually develops on the
lowest leaves in late June and early July and results in a conspicuous yellowing followed by leaf-drop.
This disease is worse during wet weather and may reappear in late summer during wet, cooler weather
and cause premature leaf yellowing and leaf-fall. Bacterial leaf blight occurs on leaves at various levels
on the soybean plant, depending on the stage of growth in relation to the rain periods favoring disease
establishment. The blighted areas of the leaves frequently drop out or tear away giving a ragged
appearance to the foliage. Downy mildew causes yellow spots on the upper sides of the leaves and
grayish tufts of mold growth on the lower surfaces of leaves. Because very little or no yield loss results
from the occurrence of these diseases, no control methods are recommended. Most level varieties appear
susceptible to these leaf diseases and continuous cropping to soybean may increase their severity.
Seed Diseases: Moldy seed at harvest results from one or more damaging diseases of soybean caused by
Phomopsis and Diaporthe fungi. Phomopsis seed decay is most serious when wet conditions prevail late
in the season as the seeds mature and before they dry down to a moisture suitable for combining.
Soybeans left in the field because of delayed harvest due to wet weather are almost sure to develop
Phomopsis infections. Moldy seed results from fungal invasion of pods and seeds. The most important
aspect of Phomopsis seed decay is the effect it has on seed germination. Moldy seed will not germinate
or seedlings die before emergence. Seeds that look healthy may often have seed coats colonized by
Phomopsis. These fungi will grow into the germinating seed and kill the seedlings before emergence.
The level of infected seeds can be determined by a standard germination test.
Producers interested in growing their own soybean seed should be particularly aware of the problems
associated with Phomopsis seed decay. Producers should avoid growing continuous soybean and harvest
those fields to be saved for seed first. Before planting, all seed should be evaluated using a standard
germination test. Use only those seed lots with 80 percent or greater germination. On those lots with 80
to 90 percent germination, adjust the seeding rate to compensate for the lower germination percentage,
and plant only if adequate soil moisture is available for rapid germination. Most fungicide seed
treatments available for use on soybean control Phomopsis. However, growers should not expect to
increase germination of diseased seed lots by more than 20 percent.
Soybean cyst nematode: Soybean cyst nematode (SCN) can be found at some level in most of the
soybean producing counties of the state. Frequently no visible symptoms of nematode damage are
observed other than reduced yield. Visible symptoms of SCN damage includes stunted, yellow plants
and weed infestations where diseased soybeans lack adequate growth. SCN is a microscopic round
worm that exists in soil as eggs, worms, and cysts. Soils with moderate to high levels of nematodes (250
to 2,000 eggs/200 cc of soil) should implement control measures to reduce nematode populations and
reduce yield losses. The only definite way to confirm the presence of SCN, or determine the level of
infestation, is to submit soil samples for laboratory analysis. Contact Ohio State University Extension's
C. Wayne Ellett Plant and Pest Diagnostic Clinic for proper soil sampling procedures and information
concerning soil analysis. The soybean cyst exists in various races that are capable of attacking different
soybean varieties. Resistant varieties are available, but they should never be planted year after year in
the same field or in fields with very high levels (greater than 2000 eggs/200 cc soil) of the nematode. A
two to three year rotation with alfalfa, corn and small grains can be used to reduce nematode populations
and rotating resistant and susceptible soybean varieties in the rotation will help keep the populations
low. Maintaining a balanced fertility program and planting early when soils are cooler and the nematode
is less active will help reduce losses from SCN.
Management Practices for Soybean Disease Control
1. Select varieties with specific resistance or partial resistance to Phytophthora root rot, or varieties
less susceptible to Sclerotinia stem rot, if these diseases have caused reduced yields on your
fields. Use soybean cyst nematode resistant varieties in fields with soybean cyst nematodes, but
only if used in a crop rotation sequence designed to reduce nematode populations.
2. Plant only well cleaned, high quality, disease-free seed with a germination of 80 percent or
greater. Treat seed with Phytophthora specific fungicides if seeds will be planted in a field with a
history of Phytophthora root rot. Plant only if adequate soil moisture is available for rapid
germination. Also treat seed with an appropriate fungicide if Phomopsis or Sclerotinia were
known to be present in seed production fields. For seed-treatment recommendations, refer to
Ohio State University Extension Bulletin 639, Seed Treatments for Agronomic Crops.
3. Improve surface and subsurface drainage to remove excess water quickly. This will reduce
damage caused by Phytophthora and Pythium damping off.
4. Rotate soybean with corn or small grains; a two- to three-year rotation is adequate under most
circumstances. Up to five years may be necessary to reduce population of Sclerotinia or at least
three years for high populations of soybean cyst nematode.
5. Incorporate residues if severe disease problems occur from leaf diseases and brown stem rot.
Tillage will improve surface drainage and reduce damage from Phytophthora root rot.
6. Weed control is especially important because weeds act as hosts for Sclerotinia white mold and
soybean cyst nematode.
7. Harvest as quickly as possible to avoid moldy seed caused by Phomopsis.
Many different types of diseases affect wheat. They can be classified as seed-borne diseases, leaf and
head blight diseases, crown and root rot diseases, and virus diseases.
Seed-Borne Diseases: Most problems resulting from seed-borne diseases have been eliminated by
highly effective seed-treatment fungicides. Several seed-borne diseases are of concern to wheat growers.
They are seed-borne scab, seed-borne Stagonospora (previously known as Septoria), common bunt
(stinking smut), and loose smut. Seed-borne scab and Stagonospora are discussed later in the section on
leaf and head blight diseases. Both diseases result in lightweight, shriveled kernels that may be moldy.
Producers should follow the recommendations listed below for proper seed cleaning and planting to
reduce seedling blight and stand losses resulting from planting diseased seed.
The two smut diseases, stinking smut and loose smut, can be particularly devastating. Stinking smut
causes losses by giving the seed of diseased plants a foul, fishy odor, making the grain unfit for milling.
Producers have been docked severely when attempting to sell smutty grain. Loose smut affects plants
and yield by converting the grain and parts of the head to smut spores. Therefore, infected plants have
no grain left to harvest. There are no varieties resistant to stinking smut, and numerous races of the loose
smut fungus exist.
Note the following guidelines to control seed-borne diseases and seedling blights:
1. Plant the highest-quality, disease-free seed possible. Seed-production fields should be inspected
from the head-emergence growth stage through harvest for occurrence of scab, Stagonospora
glume blotch, loose smut, and stinking smut. Do not use seed from severe smut infested fields.
2. Clean seed thoroughly to remove all shriveled, lightweight kernels. This may require raising the
test weight of the grain by several pounds per bushel.
3. Have a standard germination test run on the seed. Use only seed with 80 percent or greater
germination percentage. If poor germination is due to Fusarium head scab, certain seed treatment
fungicides can improve germination by 15 to 20 percent.
4. All wheat seed should be treated with a seed-treatment fungicide effective for control of smut
fungi, Fusarium scab and Stagonospora. More information on seed-borne and soilborne diseases
and seed treatment fungicides is available in Ohio State Extension Bulletin 639, Seed Treatments
for Agronomic Crops, available at your local county Extension office.
5. Plant in a well-prepared seed bed or with a no-till drill capable of proper seed placement, when
soil moisture is adequate and soil temperatures are not too high. Plant after the Hessian fly safe
date for your county to help avoid seedling diseases.
Leaf- and Head- Blight Diseases: Major diseases in this group are powdery mildew, leaf rust, Septoria
tritici leaf blotch, Stagonospora (Septoria) nodorum leaf and glume blotch, and Fusarium head scab. All
can cause major yield losses, but their occurrence is essentially weather-dependent. Cool, rainy weather
from mid-April through the flowering period of the wheat plant in late May to early June favors the
development of most of these diseases. They require either the leaf surfaces to be wet for a certain
period of time or the relative humidity within the plant canopy to be near 100 percent. Powdery mildew
and Septoria tritici leaf blotch are the first leaf diseases to occur in the spring. Both are favored by cool,
humid, or wet weather. Leaf rust and Stagonospora nodorum leaf blotch require slightly warmer
weather, thus they follow in mid to late May. Stagonospora nodorum glume blotch and Fusarium head
scab become evident in June soon after flowering, especially if wet weather persists through this time.
The use of resistant varieties is the major control procedure for these disease management, leaf, and
head blight diseases. Few varieties are resistant to all of these diseases. Determine which diseases cause
most consistent problems in your area, and choose a variety based on its level of resistance. The level of
fungal carryover from one wheat crop to the next is minimal if a two-to three-year rotation away from
wheat is maintained. Rotation is a primary control measure for powdery mildew and the Septoria and
Stagonospora diseases. Spores of leaf rust are blown up from the southern states in late May; therefore,
crop rotation has little effect on the incidence of leaf rust. Adequate and balanced fertility, to provide
optimum nutrition for hardy plants, helps lessen the adverse effects of foliage diseases. High rates of
nitrogen will favor powdery mildew and Stagonospora leaf and glume blotch. Head scab is usually more
severe when wheat is planted after corn because the fungus causing scab is the same one that causes
Gibberella stalk rot. When possible, wheat should follow soybean or other legumes in the cropping
Fungicides are available to control most foliar diseases of wheat. However, the use of these fungicides
should be based on sound economic decisions and the level of disease in the field. Fungicides have been
profitable during years when foliar diseases have been severe on susceptible cultivars or in locations
where diseases are a persistent problem. Obtain a copy of Extension Bulletin 735, Wheat Disease
Control in Ohio or contact your local county Extension office for up-to-date information on fungicide
recommendations for wheat or consult the Ohio State University Extension Website Ohioline
Crown and Root Rot Diseases: Two of the more important crown- and root-rot diseases are take-all
and Cephalosporium stripe. Both of these diseases are soilborne, meaning that the fungi that cause these
diseases reside in the soil. Take-all can be recognized by examining the roots and lower stems of
prematurely killed plants. The base of the stem and roots will have a scurfy, black appearance.
Cephalosporium stripe disease is characterized by alternating yellow and brown stripes that extend the
entire length of the leaf blades. Both of these diseases are favored by planting wheat year after year in
the same field. Usually a rotation sequence with a break of two years or more between wheat crops will
eliminate fungal carryover. The exception to this is when no-till is used to produce all crops in the
rotation sequence and wheat residues do not decompose before the next wheat crop is planted. The other
exception to this is when perennial grass weeds, such as quack grass, become established in the field.
Proper rotations, tillage and elimination of grass weeds have been highly effective in managing both
diseases. Additional control of the stripe disease can be achieved by maintaining a soil pH above 6.2 by
proper liming according to a soil test. Adequate soil fertility will also reduce yield losses from root
Virus Diseases: Wheat spindle streak mosaic (yellow mosaic) and barley yellow dwarf are the two most
common virus diseases. Wheat spindle streak mosaic is a soilborne disease that is usually recognized in
early May as the stems of the wheat plant begin to elongate. The upper leaves of affected plants will
show short, spindle-shaped, yellow streaks. These symptoms may intensify if weather remains cool. The
symptoms will tend to disappear as the weather begins to warm. Control of wheat spindle streak is
achieved through the use of resistant varieties. A number of highly-resistant varieties are available.
Barley yellow dwarf virus is transmitted by aphids. Aphids arriving from the southern states transmit the
virus to the newly-planted wheat crop in the fall. Severely affected plants may be stunted, have reddish
or yellowish leaf tips and produce no heads. Yield losses greater than 50 percent have occurred when
entire fields have been infected in the fall. Because no varieties have an acceptable level of resistance
and early-fall infections cause the greatest yield losses, wheat planting should be delayed until after the
Hessian fly safe date when aphids have ended their fall flights.
Wheat Disease Management Summary
1. Choose varieties resistant to the major foliar diseases in your area. Varieties with resistance to
wheat spindle streak mosaic, leaf rust, powdery mildew, Stagonospora leaf and glume blotch,
and head scab are available. Information on the level of disease resistance in the more common
varieties is available from seed dealers or local county Extension offices.
2. Plant only well-cleaned, disease-free seed that has a high-germination percentage. All seed
should be treated with a fungicide to manage stinking smut or loose smut, as well as seed-borne
Fusarium scab and Stagonospora. Consult Extension Bulletin 639 Seed Treatment for Agronomic
Crops for specific recommendations.
3. Plant in a well-prepared seed bed or with a no-till drill capable of proper seed placement, after
the Hessian fly safe date for your county. Plant only if soil temperature and moisture is adequate
for rapid germination and seedling growth.
4. Use a crop rotation with a minimum of two years between wheat crops. Rotations with legumes
are particularly helpful in reducing the survival of pathogens in the field. Where possible, do not
plant wheat after corn due to the increased potential of Fusarium head scab.
5. Till residues in heavily-diseased fields, especially those affected by Cephalosporium stripe or
take-all. Burying will enhance decomposition of residues and death of the disease-causing fungi.
6. Use a well-balanced fertility program and maintain a soil pH from 6.2 to 6.7. Be sure sufficient
nitrogen, potassium, and phosphorus are available for good seedling growth in the fall. Excessive
nitrogen may increase losses from foliage diseases.
7. Control grass weeds. Destroy volunteer wheat, quackgrass, and other weed grasses to reduce the
amount of certain pathogens surviving in and around fields.
8. Harvest promptly when grain moisture permits. Store grain at moisture levels no higher than 13
percent, thus preventing storage molds from growing.
9. Fungicides are available for control of many foliar wheat diseases. Use of fungicides is
dependent on susceptibility of the variety, level of disease in the field, the yield potential of the
field and the price of grain. Specific recommendations for use of fungicides are available in
Extension Bulletin 735, Wheat Disease Control in Ohio or in Bulletin 811, Profitable Wheat
Management, or on Ohio State University Extension Website Ohioline (http://ohioline.ag.ohio-
There are more than a dozen diseases of alfalfa. They can be grouped into two categories: those that
affect the stems, crowns, or roots and those affecting the foliage. The stem and root rot diseases are the
most serious. Major losses of stand have been caused by Phytophthora root rot, anthracnose, and
Sclerotinia crown rot. Verticillium wilt is a constant threat because some farmers are still growing old
varieties that lack resistance to this disease. Nearly all alfalfa varieties currently grown in Ohio have
resistance to bacterial wilt and Fusarium wilt. The widespread use of resistant varieties has greatly
diminished the significance of wilt diseases.
Phytophthora root rot has been responsible for loss of stand in the seedling year when rainfall is above
average and/or surface and subsurface drainage is poor. It is caused by a soilborne fungus that becomes
active under wet soil conditions and may attack both seedlings and older plants. Dark brown, decayed
areas on the tap root two to three inches below the soil surface are early indicators of Phytophthora root
rot. Soil moisture is the key factor affecting disease development. Any improvement in surface and
subsurface drainage will reduce losses from this disease as well as from other less common root rots.
Varieties with good levels of resistance are now available. Phytophthora specific fungicide seed
treatments are available to help prevent loss of stands due to seedling damping-off. Fungicides are
labeled for use at planting either as a broadcast application or incorporated on fertilizer granules and
applied in a band beneath the seed.
Aphanomyces root rot may contribute to poor alfalfa establishment and reduced growth in wet soils.
Seedlings may die (damping off) if infection occurs at an early stage of development. Older seedlings
are yellowed and stunted. When Aphanomyces and Phytophthora occur together, they form a destructive
disease complex. Alfalfa varieties with moderate to good levels of resistance are available for control of
Aphanomyces root rot.
Anthracnose is a major cause of thinning of older alfalfa stands. Seedlings may be killed or crown and
crown buds of older plants may be affected. Wilted and dead bleached stems are characteristic of the
disease. Diamond-shaped lesions (cankers) with light-brown centers and dark margins develop on the
lower stems. Anthracnose is a warm, wet-weather disease. Resistant varieties are available. Anthracnose
has long been recognized as a destructive disease of red clover in the southern areas. The use of resistant
varieties of red clover controls this problem.
Sclerotinia crown rot occurs almost exclusively on late-summer seedlings, especially when minimum-
tillage methods are used. Affected plants wilt and the cottony-white mold changes to hard black bodies
on the crowns or lower stems. This disease is usually seen during the cooler periods of the year. Crop
rotation, with two to three years away from alfalfa, aids in control.
Verticillium wilt may be spread from field to field with infested seed and in manure from animals fed
infested hay. This soilborne disease usually does not become a problem until the third production year. It
can be recognized on scattered plants that become yellow and stunted, then gradually die, leaving a thin,
unproductive stand. Control is mainly through use of disease-free seed, resistant varieties, and crop
There are several foliage diseases of alfalfa. Any of these may cause considerable loss of leaves during
periods of prolonged wet or humid weather. Little can be done about these diseases in the year that they
occur. Proper crop rotation will help control these diseases in following years.
Alfalfa Disease Management Survey
1. Select high-yielding, winter-hardy varieties with resistance to Phytophthora root rot,
anthracnose, Verticillium wilt and Aphanomyces root rot. Consult The OSU Horticulture and
Crop Science Series 195, Ohio Forage Performance Trials for a listing of alfalfa varieties and
their level of resistance to various diseases.
2. Use seed-treatment fungicides specific for Phytophthora and Pythium to reduce losses from
damping off. Most high-quality varieties now come pretreated with fungicides.
3. Select well-drained fields. If necessary improve soil drainage to prevent excess moisture
accumulation for extended periods of time.
4. Fertilize to obtain adequate levels of nutrients for amount of forage harvested.
5. Maintain a soil pH near 7 to avoid low pH stress.
6. Plant in a well-prepared seed bed when soil moisture is adequate for quick germination and
seedling emergence. For late summer, no-till seeding, plant as early in August as possible to
avoid seedling losses due to Sclerotinia crown and stem rot.
7. Minimize traffic over the field. Crown damage from heavy equipment provides an entry way for
pathogens as well as causing soil compaction which promotes root rots.
8. Harvest on time. Proper harvest intervals will ensure adequate storage of reserves in taproots
while minimizing the buildup of disease organisms on leaves, stems and crowns.
9. Control insects, primarily alfalfa weevil and potato leafhopper, to minimize plant stress. See
Extension Bulletin 545 Insect Pests of Field Crops for insect control recommendations.
10. Rotate to corn or small grain between alfalfa crops. Never follow alfalfa with alfalfa.
IPM: MORE THAN JUST SCOUTING
Integrated pest management is far more complex than just scouting fields for pests, having knowledge of
economic thresholds, and using pesticides in a judicious fashion. A well-designed IPM program should
integrate several management strategies for insects, plant diseases, and weeds while maintaining
agricultural profitability and environmental quality. Effective pest management programs should
anticipate potential pest problems and attempt to modify existing crop production practices if they
continually lead to pest outbreaks, yield losses, and overuse of pesticides. This objective is most often
accomplished by blending pest control tactics together. The tools of pest management programs may
include cultural, mechanical, physical, biological, genetic, regulatory, and chemical methodologies. The
successful integration of many of these strategies should optimize control of a pest rather than maximize
it. Some of the most common tactics used in field crop pest management programs include:
1. use of pest resistant crop varieties;
2. rotation of crops;
3. changing of tillage practices;
4. variation of planting and harvest times;
5. proper fertilization of soil;
6. proper sanitation;
7. effective water management programs; and
8. use of trap crops.
Pesticide Selection: Making Choices if a Pesticide Is Required
The decision to use a pesticide should be based upon:
1. information obtained from scouting;
2. knowledge of economic thresholds; and
3. an awareness of the potential benefits and risks associated with a treatment.
If used improperly, pesticides can cause detrimental effects to the applicator, the crop, or the
environment. Pesticides can provide effective control, but they should be used judiciously and in
combination with nonchemical methods that can be incorporated into the cropping system. Once a
decision to use a pesticide has been made, several questions should be thought through carefully.
1. Is the pest you want to control listed on the pesticide label?
2. Does the label state that the pesticide will control the pest, or does the word "suppression" appear
on the label?
3. Are you familiar with relevant university research and recommendations?
4. Is the recommended rate of application economical for your operation?
5. How toxic is the pesticide? Dermally? Orally?
6. Is the pesticide a restricted-use product?
7. Does this pesticide have the potential to contaminate groundwater, even when label
recommendations are followed?
8. Will the use of this pesticide expose humans to health or safety risks?
9. Will the use of this pesticide threaten wildlife populations?
Although the use of pesticides can greatly enhance the production of food and fiber during outbreaks of
pests, their misuse may create adverse environmental effects. The general public will increasingly
demand accountability from those within the agricultural community who have the daunting challenge
of providing an abundant, safe, and nutritious food supply while sustaining environmental quality.
Clearly, the emphasis for the future lies in optimizing environmental quality while minimizing crop
GROWTH STAGES OF FIELD CROPS
Before applying certain pesticides, you should be able to recognize the stages of crop growth. Because
some growth stages are more susceptible to pest injury than others, the economic threshold or damage
threshold may not be the same at each stage. The growth stages of corn, soybeans, small grains and
sorghum are illustrated. Become familiar with these growth stages and the various plant parts. In reading
this manual, refer to the illustrations whenever stages of crop growth are mentioned in discussions of
economic thresholds or timing of pesticide applications.
Vegetative (V) Stages
The vegetative stages are defined according to the uppermost leaf on which the leaf collar is visible. The
leaf collar is the region between the leaf blade and the leaf sheath. All of the vegetative stages of corn
development are not presented, but these are representative ones.
Stage VE: Emergence. The coleoptile, a protective sheath that surrounds the shoot, emerges. The first
leaf emerges from within the coIeoptile, and other leaves will emerge from within the sheath of the
previously emerged leaf. The growing point of the plant is protected beneath the soil surface from hail,
frost, and wind.
Stage V1: First-leaf stage. The collar of the first leaf is visible and other leaves are emerging.
Stage V6: Sixth-leaf stage. The collar of the sixth leaf is visible. The stalk is beginning to elongate and
the growing point is above the soil surface.
Stage V12: Twelfth-leaf stage. Stalk is elongating rapidly. The size of the ears and the number of
potential kernels on each car are being determined.
Stage V18: Eighteenth-leaf stage. The tip of the tassel is visible. Brace roots are produced. Stage VT:
Tasseling. The last branch of the tassel is completely visible. This stage begins approximately 2 to 3
days before silking begins.
Reproductive (R) Stages
Stage R1: Silking stage. Silks growing from the base of the ear are visible first and those growing from
the ear tips emerge last. Pollination occurs and determines the number of kernels on each ear.
Unpollinated ovules result in barren kernels.
Stage R2: Blister stage. Kernels are white, blister-shaped, and contain about 85 percent moisture.
Kernel inner fluid is abundant and clear.
Stage R3: Milk stage. Kernels are yellow and contain approximately 80 percent moisture. Inner fluid is
milky white because of accumulating starch. Silks are brown and dry.
Stage R4: Dough stage. Kernels contain approximately 70 percent moisture. Inner fluid thickens to a
doughy consistency. Kernels begin to dent.
Stage R5: Dent stage. All kernels are dented or denting and contain about 55 percent moisture.
Stage R6: Maturity black layer formation. All kernels have accumulated their maximum amount of
dry matter. A black or brown layer forms on each kernel, beginning with those on the ear tip and
progressing to the basal kernels. Kernel moisture is about 30 to 35 percent, although it varies with
hybrids and environmental conditions.
Vegetative (V) Stages
The vegetative stages are defined according to the uppermost fully developed leaf node the one in which
the leaves above it have unrolled leaflets (leaflet edges not touching). All of the vegetative stages of
soybean development are not described, but these are representative ones.
Stage VE: Emergence. Hypocotyl elongates toward the soil surface, pulling the cotyledons with it. The
cotyledons, which are borne opposite each other, emerge from the soil surface and fold apart to expose
the growing point.
Stage VC: Cotyledon stage. The unifoliate (simple) leaves are unrolled. They are borne opposite each
other at the first leaf node on the stem. Except for the cotyledons, only the unifoliate leaves are produced
as a pair. Nodule formation begins.
Stage VI: First-node stage. The leaflets of the second leaf, the first trifoliate leaf, are unrolled. This
leaf occurs at the second leaf node.
Stage V2: Second-node stage. Three nodes have leaves with completely unrolled leaflets (the unifoliate
leaf node and the first 2 trifoliate leaf nodes).
Stage V3: Third-node stage. Four nodes have leaves with completely unrolled leaflets.
Stage V5: Fifth-node stage. Six leaf nodes have leaves with completely unrolled leaflets.
Stage V6: Sixth-node stage. Seven nodes have leaves with completely unrolled leaflets. By this stage,
the cotyledons and unifoliate leaves may have fallen from the plant.
Reproductive (R) Stages
Although some varieties may continue vegetative growth, the plant enters the reproductive stages as
soon as flowering begins. Flowering normally begins at the third to sixth node and progresses upward
and downward. Branches begin flowering a few days after the main stem.
Stage R1: Beginning bloom. One open flower at any node on the main stem.
Stage R2: Full bloom. Open flower at 1 of the 2 uppermost nodes on the main stem with a fully
Stage R3: Beginning pod. Pod is 8/16 inch long at 1 of the 4 uppermost nodes on the main stem with a
fully developed leaf.
Stage R4: Full pod. Pod is 3/4 inch long at l of the 4 uppermost nodes on the main stem with a fully
Stage R5: Beginning seed. Seed is 1/8 inch long in the pod at 1 of the 4 uppermost nodes on the main
stem with a fully developed leaf.
Stage R6: Full seed. Pod containing a green seed that fills the pod cavity at 1 of the 4 uppermost nodes
on the main stem with a fully developed leaf. Leaf yellowing begins with the oldest leaves and spreads
Stage R7: Beginning maturity. One normal pod on the main stem has reached its mature pod color.
Stage R8: Full maturity. Ninety-five percent of the pods have reached mature color. Five to 10 days of
drying weather are required before soybeans have less than 15 percent moisture.
Stage 1. The coleoptile, a protective sheath that surrounds the shoot, emerges. The first leaf emerges
through the coleoptile, and other leaves follow in succession from within the sheath of the previously
Stages 2 to 3. Tillers (shoots) emerge on opposite sides of the plant from buds in the axils of the first
and second leaves. The next tillers may arise from the first shoot at a point above the first and second
tillers or from the tillers themselves. This process is repeated until a plant has several shoots.
Stages 4 to 5. Leaf sheaths lengthen, giving the appearance of a stem. The true stems in both the main
shoot and in the tillers are short and concealed within the leaf sheaths.
Stage 6. The stems and leaf sheaths begin to elongate rapidly, and the first node (joint) of the stem is
visible at the base of the shoot.
Stage 7. Second node (joint) of stem is visible. Next to last leaf is emerging from within the sheath of
the previous leaf but is barely visible.
Stage 8. Last leaf, the "flag leaf," is visible but still rolled.
Stage 9: Preboot stage. LiguIe of flag leaf visible. Head beginning to enlarge within the sheath.
Stage 10: Boot stage. Sheath of flag leaf completely emerged and distended because of enlarging but
not yet visible head.
Stages 10.1 to 10.5. Heads of the main stem usually emerge first, followed in turn by heads of tillers in
order of their development. Sorghum brace roots produced. Heading continues until all heads are out of
their sheaths. The uppermost internode continues to lengthen until the head is raised several inches
above the uppermost leaf sheath.
Stages 10.5.1 to 10.5.3. Flowering progresses in order of head emergence. Unpollinated flowers result
in barren kernels.
Stage 10.5.4: Premilk stage. Flowering is complete. The inner fluid is abundant and clear in the
developing kernels of the flowers pollinated first.
Stage 11.1: Milk stage. Kernel fluid is milky white because of accumulating starch.
Stage 11.2: Dough stage. Kernel contents soft and dry (doughy) as starch accumulation continues. Plant
leaves and stems are yellow.
Stage 11.3. Kernel hard (difficult to divide with the thumbnail).
Stage 11.4. Ripe for cutting. Kernel will fragment when crushed. Plant dry and brittle.
Ohio Department of Agriculture Publication for Pesticide Regulation 02/05