Plant And Pest Advisory - Landscape_ Nursery_ and Turf Edition

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LANDSCAPE, NURSERY & TURF EDITION                                 $1.50                       APRIL 6, 2000

                                                       Diseases of Turfgrass
                                        Bruce B. Clarke, Ph.D., Turfgrass Pathology

                                        x Fungicide resistance
                                             Infectious fungi sometimes develop resistance to particular
                                        fungicides, especially when a product is used repeatedly without
                                        alternating with chemically unrelated fungicides. When fungicide
                                        resistance develops, there is no value in increasing rates, shortening
                                        intervals between sprays, or using other fungicides with similar
                                        modes of action. Fungicide resistance has been confirmed in numer-
                                        ous instances for each of the following diseases and fungicide groups:
                                        dollar spot/benzimidazole fungicides, dollar spot/DMI fungicides,
                                        and Pythium blight/metalaxyl and mefenoxam. Benzimidazoles (e.g.,
                                        Cleary 3336) and phenylamides (e.g., Subdue) have the highest risk of
                                        resistance. Strobilurins (e.g., Heritage) have a moderately high risk of
                                        resistance, DMIs (e.g., Bayleton) and the dicarboximides (e.g., Chipco
                                        26GT) have a moderate risk, and the nitriles (e.g., Daconil Ultrex)
                                        aromatic hydrocarbons (e.g., PCNB) and dithiocarbmates (e.g.,
               INSIDE                   mancozeb) have a low risk of resistance for major chemical groups.
                                             Several general strategies are recommended to minimize the risk
                                        of fungicide resistance. First, don’t rely on fungicides alone for
                                        disease control. Avoid using turfgrass varieties that are highly suscep-
                                        tible to common diseases. Integrate good disease management
                                        practices to reduce the possibilities of a fungus developing resis-
Diseases of Turfgrass ............. 1   tance. Limit the number of times at-risk fungicides are used during
                                        the growing season. Alternate at-risk fungicides with different
Common Diseases of                      fungicide groups. When using an at-risk fungicide, tank-mixing with
Deciduous Ornamentals ........ 2        another fungicide from another chemical group (different mode of
                                        action) can also reduce the risk of resistance. These are general
                                        principles that can help reduce but not eliminate risk. A fungicide-
Rust Diseases in                        resistant pathogen population can still develop when these principles
Ornamental Plantings ............ 4     are practiced. Finally, refer to product labels before tank-mixing
                                        products to ensure compatibility and to avoid phytotoxicity.
                                        x Necrotic ring spot
                                              This disease, caused by the fungus Ophiosphaerella korrea
                                        (formerly Leptosphaeria korrea), is apparent on landscape turf at this
                                        time. Ophiosphaerella attacks the roots and crowns of turf during
                                        cool, wet weather in the spring and fall. Grass growing under stress
                                        (i.e., low mowing height, pH extremes, or moisture extremes is most
                                        susceptible to infection. Although most cool season grasses are
                                                                SEE TURFGRASS ON PAGE 2
VOL. 6 NO. 3                                                                                             PAGE 1
                  TURFGRASS FROM PAGE 1
susceptible to necrotic ring spot, annual bluegrass,
                                                                  Common Diseases of
Kentucky bluegrass, and fine fescues are most fre-
quently affected. Symptoms typically appear as
                                                                 Deciduous Ornamentals
circular to irregular patches of dead turf (3" to 12" in     Ann B. Gould, Ph.D., Plant Pathology
diameter) with green tufts of resistant grass or weeds
in the center. To control, reduce plant stress, avoid soil   x Leaf spots
pH extremes, and treat affected turf now with Banner,             Leaf spots affect many deciduous ornamentals in
Cleary 3336, Eagle, Fungo, Heritage, Rubigan, or             the landscape and nursery and can be relatively
Sentinel. Repeat 28 days later for best results.             harmless to healthy plants. Each spring, the fungi that
x Red thread                                                 cause leaf spots produce spores from fruiting bodies
     This disease, caused by the fungus Laetisaria           found in last year’s infected leaves. These spores are
fuciformis, has started to develop on sensitive turf         carried to susceptible leaf tissue by wind and rain.
throughout the State. Infections are characterized by        Leaf spots will appear later in the growing season on
the appearance of short red threads (1/8” to 1/4” long)      leaves as discreet regions of dead tissue that are often
emerging from tan-colored leaf blades. Affected              bordered by a yellow “halo.” Expect to see high
patches are typically pink in color and range from 1 to      incidence of leaf spots this year if cool, rainy weather
6 inches in diameter. Although perennial ryegrass and        persists throughout the spring.
fine fescue are most susceptible, bentgrass, bluegrass,           Management of leaf spots requires a few basic
bermudagrass, and tall fescue may also be affected.          strategies: reduce leaf wetness and humidity in
Red thread is typically found on “hungry” (low fertility)    plantings (e.g., improve air-flow through proper
turf during cool, wet weather. Well fertilized turf,         spacing and weed management, irrigate during early
however, may also be attacked. To obtain optimum             morning hours, and avoid overhead watering); remove
disease control, maintain adequate fertility levels, keep    leaf litter to reduce fungal inoculum; and improve
turf properly irrigated, avoid excessive thatch, and         plant vigor to help reduce disease severity.
apply Banner, Bayleton, Chipco 26019, Compass,                    The use of fungicides for leaf spot control in the
Curalan, Eagle, Heritage, Prostar, Rubigan, Sentinel,        landscape is not usually recommended unless plants
Touche, or Vorlan per manufacturer’s recommenda-             are severely stressed. If desired, however, leaf spots
tions.                                                       may be prevented with foliar applications of Benefit*,
x Take-all patch                                             chlorothalonil, ConSyst*, copper, iprodione,
     This disease, caused by the root and crown infect-      mancozeb, maneb, propiconazole, Spectro 90WDG*,
ing fungus Gaeumannomyces graminis var. avenae, has          thiophanate-methyl, or Zyban*. In general, these
been observed on several bentgrass greens, tees, and         preventive fungicides are applied at budbreak and the
fairways during the last week. Although infection takes      spray repeated twice at 7- to 14-day intervals. Check
place during cool, wet weather in the spring and fall,       individual labels for specific host and application rate
symptoms are most striking after stress. Infected grass      recommendations.
first appears bronze to reddish-brown in color and           x Scab
then fades to a dull brown. Patches are usually circular          Scab, caused by the fungus Venturia, is one of the
or ring-shaped and range in size from several inches to      most common diseases of apple, crabapple, and other
two feet or more in diameter. The centers of affected        rosaceous ornamentals such as cotoneaster, hawthorn,
turf are frequently colonized by fescues, (Festuca spp.),    mountain ash, and pyracantha. Symptoms of scab
bluegrass (Poa spp.) or weed species. Upon close             appear as olive-colored spots with fuzzy borders on
examination, decaying roots and leaf sheaths appear          infected leaves and petals. Fruit affected by the
black and dark strands of mycelium often develop             disease develop bumpy, corky lesions, and severely
parallel to the root axes. The disease is enhanced by        affected leaves, petals, and fruit may prematurely drop
poorly drained, light-textured, and high pH soils.           from the tree.
While take-all is difficult to control, best results have         Like leaf spots, disease development in scab
been achieved through the use of acidifying fertilizers      occurs in the spring. Spores are forcibly ejected from
during cool weather (caution: ammonium sulfate can           fruiting bodies in leaves infected the previous year.
burn turf is applied during warm, humid weather) and         Newly infected leaves produce more spores that go on
preventive fungicide applications (i.e., Banner,             to infect fruit and other leaves through the spring
Bayleton, Heritage, or Rubigan) in late October,             period. Cultural disease management strategies,
November, March and April. Whenever practical,               similar to those used for leaf spots; include the use of
overseed with less susceptible grasses such as fine          varieties resistant to scab. To prevent severe defolia-
fescue, Kentucky bluegrass, or perennial ryegrass to         tion of sensitive hosts, apply chlorothalonil, Consyst*,
mask symptom expression. t                                                      SEE SCAB ON PAGE 3

PAGE   2                                                                                                VOL. 6 NO. 3
                    SCAB FROM PAGE 2                       conditions no longer favor disease development.
fenarimol, lime-sulfur, mancozeb, maneb,                   Kousa dogwood (Cornus kousa) does not seem to be
myclobutanil, Phyton 27, propiconazole, Spectro            infected by anthracnose under normal growing
90WDG*, thiophanate-methyl, triflumizole (enclosed         conditions and may offer an alternative to flowering
structures only), or Zyban* from budbreak until 2          dogwood where dogwood anthracnose has been
weeks after petal fall. See individual labels for timing   troublesome in the past.
and rates.                                                 x Cankers of deciduous trees
x Tar spot of maple                                             In the last issue of this newsletter, canker diseases
     The fungus that causes tar spot infects maple         that commonly occur on conifers were discussed. As
leaves in the spring, but the thickened, black blotches    in conifers, deciduous trees are predisposed to canker
of fungal growth that characterize the disease don’t       by environmental problems, particularly drought
appear until late summer. The damage due to tar spot       stress. We can expect to see a good deal of canker
is merely cosmetic and appears too late in the growing     development on plant material that was subject to
season to seriously affect trees. To manage this           drought stress last year.
disease, improve plant vigor, avoid over-head watering,         Cankers appear as large, elliptical lesions on twigs,
and rake up and remove diseased leaves to reduce           branches, and trunks. These lesions kill vascular
inoculum. If desired, apply copper or mancozeb prior       tissue, so tissue distal to the canker often dies. Fungi
to bud swell (see label for specific recommendation).      that commonly cause cankers on deciduous tress in
x Anthracnose of shade trees                               New Jersey include Nectria, Botryosphaeria, and
     Sycamore, ash, maple, oak, and walnut are suscep-     Cytospora. Fungicides are ineffective against canker
tible to anthracnose of shade trees during wet spring      diseases, so management techniques include improve-
weather. Diseased leaves appear “scorched” along           ment of plant vigor and pruning of moderately af-
veins and leaf margins, and twig and branch dieback        fected trees. When pruning for disease control,
may occur on trees in poor health or stressed due to       remove branches at least 6- to 8-inches below discol-
severe environmental conditions. Leaves infected with      ored tissue. Prune during dry weather, and surface
anthracnose are often shed by mid-summer. If de-           sterilize pruning tools between cuts using denatured
sired, some control of this disease can be obtained        alcohol.
with foliar applications of fungicides (check labels for   x Black knot of Prunus
specific diseases) in a manner similar to that described        Black knot, caused by Apiosporina morbosa, is a
for leaf spots. In addition, Arbotect 20S and Phyton 27    widespread disease of many trees in the genus Prunus.
are available for use (see label). Prune cankers, when     On susceptible species, tree value is reduced by the
practical, to reduce disease spread.                       formation of black, spindle-shaped galls on branches.
x Dogwood anthracnose                                      Hosts such as almond, apricot, blackthorn, most
     Although dogwoods are commonly affected by            cherries, chokecherry, peach, and many wild and
several ordinary leaf spot diseases (e.g., Septoria leaf   cultivated plums are commonly affected. Black knot
spot or Elsinoe spot anthracnose), dogwood (or             can be difficult to control on susceptible trees.
Discula) anthracnose is a more serious disease that             Black knot first appears in the fall as small, light-
occasionally affects flowering dogwood (Cornus             brown swellings on current-season twigs. These
florida) in New Jersey landscapes. Since dogwood           swellings continue to enlarge through the next grow-
anthracnose, like other diseases that occur in the         ing season to form a canker or knot. Eventually the
spring, is affected by rainy weather during leaf break,    knot splits to reveal a velvety, olive-green fungal
expect to see increased disease development this year      stroma (structure bearing spores) that turns hard and
if cool, rainy weather persists.                           black the following winter. Well-developed knots are
     Symptoms of dogwood anthracnose include               black, roughened, and spindle-shaped. Although the
extensive lower branch dieback and noticeable leaf         average knot caused by Apiosporina is 4 to 12 inches
spots and blotches. Diseased trees often have clusters     in length, the swellings can enlarge yearly and grow
of water sprouts on the main trunk. As anthracnose         each season closer to the base of the branch. Knots
progresses, branches die from the ground upward and        eventually girdle affected branches, and tissue distal to
the tree is eventually killed. Drought stress and winter   the knot dies. Occasionally, the fungus will grow into
injury can increase disease severity. For best results,    the main trunk, girdling the tree and killing it.
remove dead or cankered branches during dry                     An integrated approach to control of black knot
weather, control borers and leaf infecting fungi, and      begins with the selection of planting material that is
maintain optimum growing conditions. To control the        free from disease. In addition, ensure plant vigor with
leaf spot phase of this disease, apply chlorothalonil,     proper pruning, fertilization, and irrigation. Decrease
copper, mancozeb, maneb, or propiconazole at               humidity in the tree and around the planting through
budbreak and repeat twice at 14-day intervals or until                      SEE BLACK KNOT ON PAGE 4
VOL. 6 NO. 3                                                                                                  PAGE 3
             Rust Diseases in                              rainy weather in the spring. These spores are spread
                                                           by wind to new leaves and fruit of rosaceous hosts,
           Ornamental Plantings                            including apple, crabapple, hawthorn, and quince. By
                                                           mid-summer, rusty orange pustules appear on infected
Ann B. Gould, Ph.D., Plant Pathology                       leaves (cedar-apple rust and quince rust) and young
                                                           stems, petioles, and fruit (quince rust). By mid- to late

    R    ust diseases are unique because many of the
         fungi that cause them require more than one
host plant (known as alternate hosts) to survive. Such
                                                           summer, spores produced in these pustules are carried
                                                           by the wind to cedar and juniper. Although these rusts
                                                           are rarely destructive on cedar and juniper, they can
rusts that regularly affect New Jersey landscapes plants   cause premature defoliation, stunted growth, swollen
include ash rust, hollyhock rust, and cedar-apple,         and distorted twigs and petioles, and poor quality fruit
hawthorn, and quince rusts (known collectively as the      on susceptible rosaceous hosts.
Gymnosporangium rusts).                                         If desired, protect susceptible rosaceous hosts
x Ash rust                                                 with chlorothalonil, Consyst*, fenarimol, flutolanil,
     The alternate hosts of ash rust, caused by the        mancozeb, maneb, myclobutanil, propiconazole,
fungus Puccinia, are ash trees and salt marsh or           Spectro 90WDG*, thiophanate-methyl, triadimefon,
cordgrass. Fungal spores, produced on marsh grass in       trifloxystrobin, or Zyban* applied at 7- to 21-day
the spring, are carried by wind to susceptible ash         intervals (see label for specific timing) from pink-bud
foliage. Yellow spots quickly form on the upper            until two weeks after petal fall. With the exception of
surface of infected leaves and on petioles and stems.      triadimefon, these compounds may also be used to
Within two weeks, bright orange infection cups (called     manage apple scab on susceptible hosts. When
aecia) develop on infected petioles, stems, and lower      possible, use cultivars of crabapple and other rosa-
surface of leaves. Affected tissue puckers and swells.     ceous plants that are resistant to rusts. To help protect
Bright orange spores produced within the aecia             valuable landscape plantings, do not plant juniperous
become windborne in early summer and infect the            species near rosaceous hosts such as crabapple,
leaves of marsh grass along the coast. Severely in-        hawthorn, or quince.
fected leaves on ash trees die prematurely and drop.            To manage the Gymnosporangium rusts on cedar
     Chemical control for ash rust is usually not neces-   and juniper, prune affected branches 6 to 8 inches
sary in the landscape. To protect highly susceptible       below galls during dry weather with surface-sterilized
trees, however, apply flutolanil, mancozeb,                pruning tools. Do this now. Fungicides such as
myclobutanil, or Spectro 90WDG* at budbreak and            mancozeb, triadimefon, or Zyban* may be applied on
repeat at intervals on the label. Ash rust is more         a preventive basis to these hosts beginning in July.
severe on trees in coastal areas close to the alternate         **Combination products. For a list of common
host.                                                      and trade names of fungicides labeled for use on
x Hollyhock rust                                           ornamentals in New Jersey, refer to the March 9th issue
     Hollyhock rust, also caused by the fungus Puccinia,   of this newsletter. t
is one of the most common and disfiguring diseases of
hollyhock in New Jersey. Look for yellow, circular
lesions on the upper leaf surfaces of infected plants.
On lower leaf surfaces, swollen, orange-colored                             BLACK KNOT FROM PAGE 3
pustules appear. Stems and green floral parts may also     adequate spacing and by pruning unnecessary limbs
be affected. To control this disease, remove and           and branches. Remove wild cherries and plums in the
discard infected leaves and stalks, and spray plants       vicinity of desirable trees. Finally, remove branches
with chlorothalonil, flutolanil, maneb, Spectro            with symptoms of the disease using proper pruning
90WDG*, or triadimefon at intervals stated on the          techniques (see discussion on canker diseases). Al-
label. Common mallow is also susceptible to this           though fungicides are not recommended for use in the
disease and may serve as a source of infection. If         landscape, mancozeb may be applied for control of
common mallow is in the vicinity of hollyhock beds, it     this disease on prized trees (see label). DO NOT apply
should be removed.                                         this fungicide post-bloom.
x Gymnosporangium rust                                          **Combination products. For a list of common and
    The fungi that cause the Gymnosporangium rusts         trade names of fungicides labeled for use on ornamen-
overwinter in galls on eastern red cedar and juniper.      tals in New Jersey, refer to the March 9th issue of this
Galls of the cedar-apple rust fungus grow to several       newsletter. t
inches in diameter, whereas galls of the quince rust
fungus are small and spindle-shaped. Bright orange,
gelatinous “horns” of spores ooze from galls during
PAGE   4                                                                                              VOL. 6 NO. 3
                                                                        New Brunswick, N.J. 08901-8551
                                                                                Cook College
                                                                            18 College Farm Road
                                                                            Plant & Pest Advisory

                                                                  Rutgers -The State University of New Jersey
                                                                  U.S. DEPARTMENT OF AGRICULTURE
                                                                    Rutgers Cooperative Extension - NJAES

 RCE Specialists and Staff                                      Rutgers Cooperative Extension (RCE)
 Bruce B. Clarke, Ph.D., Turf Pathology                         provides information and educational
 Ann B. Gould, Ph.D., Ornamentals Plant Pathology
 Steven Hart, Ph.D., Weed Science
                                                                services to all people without regard to sex,
 Joseph R. Heckman, Ph.D., Soil Fertility                       race, color, national origin, disability, or
 James A. Murphy, Ph.D., Turf Management                        age. RCE is an Equal Opportunity Employer.
 George J. Wulster, Ph.D., Floriculture                         Pesticide User Responsibility: Use pesti-
 Richard J. Buckley, Coordinator, Plant Diagnostic Laboratory   cides safely and follow instructions on
 RCE County Agricultural Agents and Program Associates          labels. The pesticide user is reponsible for
 Atlantic, Charlene H. Costaris (609-625-0056)                  proper use, storage and disposal, residues
 Bergen, Joel Flagler (201-599-6162)
                                                                on crops, and damage caused by drift. For
 Burlington, Raymond J. Samulis (609-265-5050)
 Camden, James Willmott (856-566-2900)                          specific labels, special local-needs label
 Cumberland, James R. Johnson (856-451-2800)                    24(c) registration, or section 18 exemption,
 Essex, Jonathan H. Forsell (973-678-7988)                      contact RCE in your County.
 Gloucester, Jerome L. Frecon (856-881-4191)                    Use of Trade Names: No discrimination or
 Hunterdon, Winfred P. Cowgill, Jr. (908-788-1338)              endorsement is intended in the use of trade
 Middlesex, William T. Hlubik (732-745-3443)                    names in this publication. In some in-
 Monmouth, Richard G. Obal (732-431-7261)
                                                                stances a compound may be sold under
 Morris, Pedro Perdomo (973-285-8307)
 Ocean, Deborah Smith-Fiola (732-349-1246)                      different trade names and may vary as to
      Steven Rettke, Program Associate IPM                      label clearances.
 Somerset, Nick Polanin (908-526-6293)                          Reproduction of Articles: RCE invites
 Union, Madeline Flahive-DiNardo, Prog. Assoc. (908-654-9854)   reproduction of individual articles, source
 Warren, William H. Tietjen (908-475-6505)                      cited with complete article name, author
 Newsletter Production                                          name, followed by Rutgers Cooperative
 Jack Rabin, Assistant Director, NJAES
                                                                Extension, Plant & Pest Advisory Newsletter.
 Cindy Rovins, Editor and Designer
 Mary Ann Hughes, Assistant Editor