Kennelly, Megan, Anthracnose of Bentgrass and Annual Bluegrass Putting Greens, Manhattan, Kansas, Kansas State University, July 2008

Kennelly, Megan M.

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Annual bluegrass and creeping bentgrass putting greens are susceptible to turfgrass anthracnose, a disease caused by the fungus Colletotrichum cereale (formerly called Colletotrichum graminicola). This fungus is sometimes found on dying leaves of Kentucky bluegrass and tall fescue during periods of heat or moisture stress, but is not consid-ered a serious problem on these turfgrass species.SymptomsAnthracnose may occur throughout the growing season but is most common in the heat of summer. From a distance, affected turf appears unhealthy and has a yellow or bronze cast (Figure 1). The turf wilts rapidly during midday and requires frequent irrigation. The disease is worse on annual bluegrass than bentgrass.Distinct leaf spots are not formed. Instead, individual leaf blades fade from dark to light green and then yellow. The youngest leaf is the last to change color. The fungus produces black structures (called acervuli) with spiny hairs (called setae) on leaves and crowns that are easily visible with a 10X hand lens (Figures 2 and 3). Acervuli can be found on naturally senescing (dying, old) tissue, where Colletotrichum is a secondary pathogen. Visible acervuli on green tissue strongly indicate that anthracnose is the primary pathogen.Basal crown rot occurs when the anthracnose fungus infects the crown. Plants with basal crown rot are killed, resulting in a thinning of the turfgrass. Acervuli and small, black fungal resting structures are visible with a hand lens (Figure 4).Anthracnose of Bentgrass  and Annual Bluegrass Putting GreensMegan Kennelly, Plant PathologistKansas State University Agricultural Experiment Station and Cooperative Extension ServicePlant Pathology  EP-147Figure 4. Black fungal growth is visible on the crown in the basal rot phase of anthracnose. Photo courtesy PACE Turfgrass Research Institute (www.paceturf.org).Figure 3. Close-up view of spiny hairs (setae). Photo courtesy PACE Turfgrass Research Institute. (www.paceturf.org)Figure 1. Bronze cast on a mixed bentgrass/annual bluegrass green. Photo courtesy PACE Turfgrass Research Institute. (www.paceturf.org)Figure 2. Black spore-producing structures (acervuli) mark the spore-producing bodies on the yellow leaves. Photo courtesy PACE Turfgrass Research Institute. (www.paceturf.org)Control Anthracnose is difficult to control after symptoms appear. The best strategy is to prevent anthracnose by alleviating the underlying stresses that trigger disease development. Nutrition: Do not starve the turf during the summer months. Light, frequent fertilizations may help the turf withstand stresses and recover quickly from anthrac-nose damage. For example, in recent studies at Rutgers University, maintaining nitrogen at 3.0 pounds per 1,000 square feet per year was key to anthracnose management. During summer months, weekly applications of nitrogen at 0.1 pounds per 1,000 square feet reduced disease by 25 to 73 percent compared to the same amount applied monthly. A good strategy is to apply about 0.5 pounds nitrogen per 1,000 square feet per month divided into weekly or biweekly applications.Mowing: Low mowing heights can increase anthrac-nose development. At heights at or below 1/8 (0.125) inch it is extremely difficult, or even impossible, to prevent anthracnose with fungicides. Recent studies at Rutgers, The State University of New Jersey, indicate that raising the mowing height slightly (as little as 0.015 inch) can decrease anthracnose severity. In those same studies, con-trary to expectations, increasing the frequency of mowing (double-cutting) did not increase the disease severity. Use walk-behind mowers on greens with a history of the disease. Also mow the perimeter of the green (the so-called clean-up lap) every other day to prevent compaction. If anthracnose is present, do not mow when the greens are wet.Other Cultural Practices: Anthracnose tends to be more severe on putting greens with poor air move-ment and poor drainage. Don’t overwater putting greens: excessive soil moisture may damage roots and decrease photosynthesis. This puts the grass into a highly vulnerable state and predisposes it to anthracnose injury. On greens with a history of the disease, consider a rigorous aerifica-tion program in fall and spring. Deep tine or core aerify in the fall. Compacted greens may be periodically aerated by spiking, slitting, or hydro-jecting. It has been assumed that topdressing increases anthracnose by introducing wounds. However, in recent trials at Rutgers, light, frequent topdressing increased anthracnose temporarily but actu-ally reduced it overall later in the summer. Those trials are ongoing and more definitive results will be reported in the coming 1 to 2 years. FungicidesSeveral fungicides (see table) are labeled for anthrac-nose control. All products work best when applied on a preventive or early curative schedule. Once anthracnose is severe, fungicides are not very effective. Furthermore, some strains of the anthracnose pathogen may be resistant to certain fungicides (see table). Follow label instructions about resistance management. Rotate to different chemis-tries (different mode of action), and consider tank-mixes with a contact fungicide. Preventive applications of reduced rate tank mixes of a DMI fungicide (see table) and chlo-rothalonil at 2-week intervals have provided good control of anthracnose in some studies. Remember that high rates of DMI fungicides on putting greens can cause undesired growth-regulator effects especially in summer.During an anthracnose outbreak avoid excessive “rescue” applications. Superintendents may try multiple products at frequent intervals in the hopes of reversing damage from anthracnose. In most cases, these attempts fail. Anthracnose is almost always associated with an underlying environmental or management-based stress. The most rapid improvement from anthracnose damage occurs following significant (cooler) weather changes and less stressful management practices.Kansas State University Agricultural Experiment Station and Cooperative Extension ServiceEP-147 July 2008K-State Research and Extension is an equal opportunity provider and employer. Issued in furtherance of Cooperative Extension Work, Acts of May 8 and June 30, 1914, as amended. Kansas State University, County Extension Councils, Extension Districts, and United States Department of Agriculture Cooperating, Fred A. Cholick, Director.Brand names appearing in this publication are for product identification purposes only. No endorsement is intended, nor is criticism implied of similar products not mentioned. Persons using such products assume responsibility for their use in accordance with current label directions of the manufacturer.Publications from Kansas State University are available on the World Wide Web at: www.oznet.ksu.eduContents of this publication may be freely reproduced for educational purposes. All other rights reserved. In each case, credit Megan Kennelly, Anthracnose of Bentgrass and Annual Bluegrass Putting Greens, Kansas State University, July 2008.Table 1. Fungicides labeled for anthracnose.Active ingredientFungicide group Efficacy and notesTypical application interval (days) Examples of productsAzoxystrobin* QoI(strobilurin)Good to excellent, at risk for fungicide resistance 14-28 HeritageBacillus licheniformis Biological control Limited data available 3-14 EcoGuardBacillus subtilis, strain SQT 713Biological control Limited data available 7-10 Rhapsodychlorothalonil chloronitrile good 7-14 Daconil Ultrex, Manicure, Concorde SST, Chlorostar, Echo, Pegasus Lfenarimol DMI Fair to good,Possible resistance risk 30 Rubiganfludioxonil Phenylpyrolle Fair to good, 14 Medallionfluoxastrobin QoI(strobilurin)Limited data available, at risk for resistance 14-28 Disarmhydrogen dioxide Oxidizing agent Limited data available 7 Zerotolmyclobutanil DMI Fair to good,Possible resistance risk 14-21 Eaglepolyoxin D Polyoxin Good to excellent 7-14 Endorsepropiconazole DMI Good, possible resistance risk 14-28 Banner, Spectatorpyraclostrobin QoI(strobilurin)Good to excellent, at risk for fungicide resistance 14-28 Insigniathiophanate-methyl Benzimidazole Fair to good, at risk for resistance 10-14 Cleary’s 3336, Fungo, Systec 1998, Cavalier, T-Stormtriadimefon DMI Fair/inconsistent,possible resistance risk 14-45 Bayleton, Proturf Fungicide VIItrifloxystrobin QoI(strobilurin)Good to excellent, at risk for resistance 14-21 Compasstriticonazole DMI Good to excellent, possible resistance risk 14-28 Trinity* Resistance to azoxystrobin and thiophanate methyl has been reported in several states. Other QoI (strobilurin) fungicides have the same mode of action as azoxystrobin and might also be at risk. DMI resistance was reported in California in 2007. Follow labeled instructions for resistance management for all fungicides.Table modified with permission from Chemical Control of Turfgrass Diseases 2008 by P. Vincelli and A.J. Powell, University of Kentucky.

Anthracnose of bentgrass and annual bluegrass putting greens

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Anthracnose of bentgrass and annual bluegrass putting greens

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