Plant & Soil Sciences Extension
368 Ag Hall
Stillwater, OK 74078
September 19, 2008
www.pss.okstate.edu/extension/index.htm Volume 1 Issue 21
Considerations when rotating wheat behind corn
Crop rotations can provide tremendous benefits to Okla‐
homa wheat growers, especially those who are no‐tilling.
Rotational crops are very effective at breaking weed and
IN THIS ISSUE disease cycles and spread risk by diversifying production
and marketing cycles. Corn is frequently used as a rota‐
• Wheat behind corn tional crop in northeastern Oklahoma and irrigated fields in
the Panhandle. Corn has also grown in popularity in central
and western Oklahoma in recent years. Much of this in‐
• Ryegrass control
crease in acres is due to better corn hybrids and improve‐
ments in no‐till planting equipment. While corn provides a
good rotational crop for wheat farmers, there are some Figure 1. Wheat infected with Wheat Streak
• We need pictures important potential stumbling blocks that can arise when Mosaic Virus and High Plains Virus. Note the
sowing wheat into corn residue. This fact sheet will discuss yellow mottling and streaking present on leaves.
• Wheat protein re- three of the most prevalent wheat disease problems that Photo courtesy of Dr. C. Rush, Texas A&M Uni‐
port available can potentially derail a wheat crop sown into corn residue. versity.
Many wheat farmers are familiar with wheat streak mosaic virus (WSMV) & the high plains virus
• Upcoming events (HPV). WSMV and HPV are transmitted by the wheat curl mite. Mites and these viruses survive in
crops such as corn, as well as many grassy weeds and volunteer wheat. In the fall, mites spread from
these crops to emerging seedling wheat, feed on that seedling wheat, and transmit the virus to the
young wheat plants. Effects of WSMV or HPV transmitted to wheat in the fall are devastating, as the
wheat plant is either killed by the next spring or will be severely damaged. In fact, data from experi‐
ments conducted at OSU reveal that fall infections typically cause as much as 55% yield loss while
spring infections cause as little as 16% yield loss.
Wheat seed treatments are not effective in controlling
WSMV or HPV. However, integrated pest management
strategies such as planting later in the fall can reduce the
likelihood of infection. A good rule of thumb is to sow
after October 1 north of I‐40 and after October 15 south
of I‐40. Since corn and volunteer wheat can serve as the
green bridge that allows the wheat curl mite to infect
seedling wheat, it is critical to completely kill corn or vol‐
unteer wheat at least two weeks prior to sowing wheat.
This strategy is effective because wheat curl mites have a
life span of 7‐10 days. Thus, chemical or mechanical de‐
struction of corn and/or volunteer wheat at least two
weeks prior to emergence of seedling wheat should
greatly reduce mite numbers in the fall. For more infor‐
mation on WSMV and HPV, see OSU Extension Facts 7636 Figure 2. Impact of fall or spring infection of
(WSMV) or go to the Plant Disease & Insect Diagnostic WSMV on wheat yield. Bars represent the yield of
Laboratory web page at: http://www.ento.okstate.edu/ fall or spring infected wheat as a percentage of
ddd/hosts/wheat.htm. non‐infected wheat.
Page 2 Plant and Soil Sciences Extension Newsletter
Another potential pitfall commonly associated with wheat following corn
is Fusarium Head Blight (FHB) Wheat farmers in the eastern and north‐
central U.S. are acutely familiar with FHB and the devastating effects it
can have on a wheat crop. Wheat farmers in the Southern Plains, how‐
ever, have largely avoided this disease in the past.
As the name indicates, FHB is caused by a group of fungi known as Fusa‐
rium. These fungi, which are also sometimes called Gibberella, also cause
diseases in corn such as Gibberella stalk rot and Gibberella ear rot. Breed‐
ing efforts have reduced the effect of these diseases on corn yield; how‐
ever, Fusarium is still frequently present on corn residue. If this residue is
left on the soil surface, as would be the case in a no‐till or minimum‐till
production system, it serves as a source of Fusarium spores for infection
of wheat. While FHB is most frequently associated with wheat following Figure 3. Early‐sown, dryland wheat (foreground) with signifi‐
corn, Fusarium can also be present on small grains residue and FHB can cant damage from WSMV and HPV. This is in contrast to the
occur in fields that have been sown behind crops other than corn. healthy late‐sown, irrigated wheat field in the background.
Photo courtesy of Dr. C. Rush, Texas A&M University.
Wheat is most susceptible to FHB at the flowering stage of development,
although some infection can still occur after flowering. Air temperatures
between 65 and 86º F and moist conditions favor reproduction of the
fungus on crop residues and infection of the wheat crop. Having these
environmental conditions during flowering are most likely in eastern
Oklahoma and less likely west of I‐35. A Fusarium Head Blight risk as‐
sessment tool is available at www.wheatscab.psu.edu and can be used
to assess the frequency with which favorable environmental conditions
for FHB might occur.
There are several options for reducing the likelihood that FHB will im‐
pact your wheat crop. If tillage is an option, the burying of crop residue
will reduce the amount of Fusarium present for infecting wheat. If tillage
is not an option, altering rotations such that wheat is sown following a
legume crop rather than a grass crop will reduce likelihood of FHB infec‐
tion. Another option is to rotate to a non‐susceptible crop such as win‐
ter canola or rapeseed. Some fungicides have show efficacy in reducing
Figure 4. Fusarium growing on corn residue can serve as a
incidence and severity of FHB. Timing of the fungicide application for
FHB control, however, is critical and is generally later than the optimal source for infection of wheat heads during or after flowering.
timing for control of foliar disease in Oklahoma. Similar to spring freeze Note the pink Fusarium fungi growing on the piece of corn
injury, it is wise to spread acres evenly among wheat maturities, as envi‐ residue and the differing levels of Fusarium Head Blight occur‐
ronmental conditions might not be favorable for FHB development dur‐ ring on the wheat heads.
ing flowering of all varieties. Finally, some crop insurance policies in‐
clude protection against crop losses associated with FHB.
In summary, crop rotation is a powerful tool in increasing crop yield and combating weeds and disease. There are some potential
disease problems that can occur when rotating small grains following corn. Farmers should be aware of the risks and take measures
to reduce risk whenever possible. For most farmers, however, the risk of WSMV, HPV, or FHB should not be viewed as a reason not
to rotate or no‐till.
Jeff Edwards This article was taken from OSU
Small Grains Extension Specialist Fact Sheet # PSS‐2136 which is
available on the web at
Bob Hunger www.wheat.okstate.edu
Page 3 Plant and Soil Sciences Extension Newsletter
Ryegrass control options for fall 2008
If you had ryegrass in your wheat this year, it was easy to see, with long slender
curving seedheads sticking up several inches above the wheat. If it is very thick,
the wheat and the ryegrass probably lodging before harvest. The ryegrass will
stay green two weeks or more after the wheat is ready to cut, and cutting wheat
with green ryegrass can result in heating and spoiled wheat. Each ryegrass seed
falls to the ground as it ripens, and it keeps producing more seedheads even after
some seed has fallen to the ground. If you had ryegrass this year, expect to have
much more next year. Keep in mind that ryegrass is different from rye, and rye‐
grass is a much worse problem than rye. Left uncontrolled, ryegrass will take over
a wheat field in as little as two years. Ryegrass is the worst weed we have ever
had in wheat. Grazeout followed by disking or chiseling doesn’t get rid of ryegrass.
Grazeout followed by glyphosate followed by disking will get rid of most of it. Low
rates of glyphosate are not good enough, use 32 ounces. Get cattle off by mid‐
May, spray, wait a week, then disk it up.
Wheat growers should properly be concerned about ryegrass. You must be alert
for it and take aggressive steps to deal with it. otherwise, it will take over your
fields. Here are some tips for controlling and preventing rygrass in your fields:
• Don’t buy wheat seed that has any ryegrass seed it. Even if you have
ryegrass now, don’t bring in more because it may be herbicide resis‐
• Try to discourage your neighbors from seeding it in their fields for graz‐ Adult Italian ryegrass can be identified by its
ing. slender seedheads that remain green after
• Be prepared to apply a herbicide to kill it if you detect it in your field. wheat has ripened
Do NOT let it go and hope that it will go away on its own.
• It is often seeded on roadways after construction projects. Pay special
attention to waterways because it often gets into wheat fields by seed
being carried by water.
• Be certain that the broadcast fertilizer spreader that is used on your
field was not used to spread a mixture of fertilizer and ryegrass.
• Make sure that your custom harvester cleans his machine as good as he
can before he starts on your wheat. Put the header on and clean it
outside the field if possible.
Herbicides are available to control ryegrass in wheat. As with any herbicide, it is
important to apply the chemical at the right growth stage, at the right rate, with
the additives recommended on the label, and to get good spray coverage. In our
research, we have found that applying a herbicide for ryegrass too early in the fall
results in poor control because more comes up later in the fall. Mid‐October to
early December applications work good if growing conditions are good. Also,
watch for grazing restrictions on some herbicides. Some herbicides are strong As with many grass weeds, one of the easiest
enough to kill ryegrass even if they are not applied until February, but the wheat ways to identify seedling Italian ryegrass is to
still suffers from ryegrass competition during the winter. To maximize wheat carefully dig up the plant and inspect the seed.
yield, kill the ryegrass by Thanksgiving. Do not expect 100% control from any her‐ Examples of Italian ryegrass seeds are provided in
bicide. the picture above
Some of the herbicides you should consider are:
• PREEMERGENCE applications of Finesse, Glean, or Amber at their highest rates labeled for use on wheat. When
applied preemergence, just after the wheat is seeded, these herbicides kill a lot of ryegrass IF it rains after the herbi‐
cide is applied and before the ryegrass comes up. Often times this is a good way to start killing the ryegrass, and at
the same time kill most other broadleaf weeds. Resistance to these herbicides is common in NE Texas up to Red
Page 4 Plant and Soil Sciences Extension Newsletter
• Hoelon is over 25 years old and has been very effective on ryegrass when applied in the fall after the ryegrass has
only a few leaves on it. Resistance to Hoelon is widespread in Arkansas wheat fields. After using it for several years,
resistance will likely show up in Oklahoma. Always use the highest rate listed on the label and observe the 28 day
grazing restriction. Good coverage is essential. It is a Restricted Use Herbicide due to human heath concerns which
has reduced its use. Hoelon kills wild oats, but doesn’t kill cheat or broadleaves. (Hoelon is a Group 1 ‐ACCase inhibi‐
• Maverick and Olympus should be considered cheat control herbicides and not ryegrass control herbicides. Maverick
usually kills about half the ryegrass, which isn’t good enough, and Olympus usually kills very little ryegrass. These are
good herbicides for cheat, but not ryegrass.
• Osprey (with NIS + UAN) 4.75 oz/A. is a good ryegrass control herbicide and it controls wild oats, but usually only
suppressed cheat. It has a 30 day grazing restriction. It is a Group 2 ALS inhibitor (mesosulfuron‐methyl). Resistance
is a problem in NE Texas.
• Olympus Flex (Olympus + Osprey) has proven popular with many applicators and growers. In our research, we get
better ryegrass control when Olympus Flex is applied with ¼% v/v surfactant in 50% UAN than with ½% surfactant in
water. Observe the 30 day grazing restriction. Control is best when weeds are small, so a fall application is needed. If
ryegrass is the main target, use a different herbicide.
• Axial XL (16.4 oz/A) is highly effective in controlling ryegrass. It is also effective on wild oats but won’t control cheat.
Therefore, if ryegrass is the only target or primary target species, it is a good choice. However, it has a 30 day graz‐
ing restriction, which often limits application to after grazing, and by then wheat grain yields will have been reduced
by ryegrass competition.
• Finesse Grass and Broadleaf has had a rough go of it since it was first introduced as a herbicide for controlling sev‐
eral problem weeds. Springtime applications are not dependable, and it doesn’t work good in drought, which is true
for many herbicides. It is only recommended west of I‐35, and at the highest rate, and only for a fall application on
ryegrass with less than one tiller. It has an ALS inhibitor mode of action.
• Beyond (Clearmax) for Clearfield wheat isn’t consistent on ryegrass. Use highest rate. The MCPA with Clearmax
doesn’t help ryegrass control. Beyond is also a Group 2 ALS inhibitor. The place for this herbicide is jointed goatgrass
• PowerFlex is new this year, has looked good on ryegrass, cheat, broadleaf weeds. However, it is also an ALS inhibitor
so resistance may quickly be a concern. It will be a good choice for broad spectrum weed control. Good crop safety.
• Crop rotation will be more important in the fight against ryegrass. Think winter canola.
• ALWAYS read and follow the label for every herbicide you use.
Oklahoma State University
A call to photographers at heart
We need the help of the states talented photographers to build a collection of images that depict nutrient deficiencies. We
are in the beginnings of building a library / diagnostics tool. The goal is to have 2 to 3 images of each nutrient deficiency in
each crop grown in Oklahoma. We need close ups and panoramas. The deficiencies can be in the wheat crop or your
neighbor’s roses. The description of each nutrient deficiency will be available online along with the pictures that you submit.
The pictures will also include field descriptions and location if available along with the photographer’s name. If you remain to
be anonymous that is fine. So we are not flooded with pictures, only send your best two of each topic. If you happen to wan‐
der across an unknown deficiency, snap a picture anyways, you can still send it even if you are unsure of what it is about. Digi‐
tal photos are preferred and the higher the resolution the better. If you have excellent pic‐
tures from a 35mm they will also work. Feel free to contact me if you have any questions. If
you already have good pictures send them my way, if not don’t worry just keep your eyes open
and cameras on and ready.
Extension Precision Nutrient Management Specialist
Page 5 Plant and Soil Sciences Extension Newsletter
• Fall Peanut Field Tours
• September 23—Erick
• September 30—Ft. Cobb
• Enhancing the Adoption of Organic Production Workshop
• Tuesday and Wednesday, October 14th and 15th, 2008
• OSU/OKC Agriculture Technology Center
• Please contact Ag Conferencing or firstname.lastname@example.org for registration information
• Registration is $35.00 before September 15, 2008
• Sensors for crop management / OSU winter crop school
• December 16 & 17
• Wes Watkins Center—OSU Stillwater
• More details to come
Wheat Protein Report Now Available!
Current Report #2135 Protein Content of Winter Wheat Varieties in Oklahoma 2008 is
now available on the web at www.wheat.okstate.edu
Plant ant Soil Science Extension Subscription information
Oklahoma State University The Plant and Soil Sciences Extension Newsletter is published
368 Ag Hall in electronic format on an as needed basis throughout the
Stillwater, OK 74078 year.
Phone: To receive an electronic copy in pdf format, email Janelle
405‐744‐6130 Malone at Janelle.email@example.com. Be sure to include
Fax: the word Subscribe in the message title and include your
405‐744‐0354 name and where you are from.
Oklahoma State University, in compliance with Title VI and VII of the Civil Rights Act of 1964, Executive Order 11246
as amended, Title IX of the Education Amendments of 1972, Americans with Disabilities Act of 1990, and other fed‐
eral laws and regulations, does not discriminate on the basis of race, color, national origin, gender, age, religion,
disability, or status as a veteran in any of its policies, practices or procedures. This includes but is not limited to ad‐
missions, employment, financial aid, and educational services. This publication is printed and issued by Oklahoma
State University as authorized by the Vice President, Dean, and Director of the Division of Agricultural Sciences and
Natural Resources and has been prepared and distributed at a cost of $00.00 for 000 copies.
Octo ber 4th
Visit SUNUP on the Web at
for video clips and more information.