You Are Here: Management Updates 2008 Archive August 7, 2008

Date: August 7, 2008
Category: Diseases
Subject: Summer Diseases

After a slow start to the season with many cultural and environmental problems dominating specimens received, the UMass Extension Plant Diagnostic Lab has seen a marked increase in disease samples in the last few weeks. The most common problems are the patch diseases-Summer Patch and Take-all caused by ectotrophic (growing on the root surface) root infecting fungi.

Summer patch is caused by Magnaporthe poae, a serious disease of bluegrass. It first appears in the warm weather of summer, usually following heavy rain or irrigation. The other factor for symptom development is a soil temperature above 70˚ F. The initial infection occurs in the spring and only outer cortical tissue is infected. High temperatures and excess water push oxygen out of the soil, weakens the roots of the grass plant and allows invasion into the vascular tissue where the fungus interferes with water and nutrient uptake as well as movement of sugars from the foliage to roots. Adequate levels of nitrogen are essential for managing summer patch; without proper levels of nitrogen, fungicide treatments will be ineffective. To manage summer patch, apply one half pound of nitrogen per 1000 square feet every three weeks; slow release forms of nitrogen (such as TurfRestore™) are more effective than quick release forms. Where possible, maintain soil pH of 5.5-6.0 to reduce disease severity. Annually, apply manganese sulfate at a rate of 2 lb/acre in the spring. Aerifying, improving drainage, raising mowing height and reducing compaction will reduce disease .Water deeply and infrequently. DMI fungicides such as propiconazole (Banner Maxx™) should be applied before symptom development occurs (when soil temperatures reach 65˚ F). Once symptoms have occurred, thiophanate methyl (Cleary's 3336™) and strobilurin (Heritage™) fungicides manage summer patch best although some turf loss will be encountered. Repeat application every four weeks                 

Take-all patch is caused by Gaeumannomyces graminis. This disease is most serious on newly established creeping bentgrass turfs, rebuilt greens or tees on old courses, and on sandy soils. The pathogen primarily infects the crown and root of the plant, usually in the cool, wet weather of spring and fall; symptom expression often does not occur until the summer stress period. This disease reaches its peak in 3-5 years, and then gradually declines due to the build-up of natural antagonistic microflora. Take-all is favored by high pH and can be reduced by acidifying fertilizers like ammonium sulfate applied with caution to avoid high salt injury. Other soil conditions that favor the pathogen include light soil texture, low organic matter, and manganese deficiency. Apply potassium, phosphorous, and manganese (if deficient) based upon the results of a soil test. Manganese sulfate at 1-2 lb Mn/A can reduce the severity of Take-all, Apply azoxystrobin (Heritage™), fenarimol (Rubigan™), propiconazole (Banner™), or triadimefon (Bayleton™) according to label instructions after the first mowing, followed by a second application in 30 days. Repeat in late summer following the first night when temperatures fall below 50º F.

Foliar anthracnose is often seen in addition to these root diseases as a result of turfgrass stress caused by root dysfunction. Anthracnose foliar blight is caused by Colletotrichum graminicola. This disease occurs throughout the world and on all species of turfgrass. The fungus causes stem lesions that can eventually girdle the tiller, causing patches of plants to yellow and die. The fungus also infects the roots and crowns of plants and is commonly found on the foliage of the grass plant. When atmospheric humidity is high and leaves wet, fruiting bodies form on dead tissue and the conidia can be blown, splashed, or spread by mowers to infect other plants. Conditions necessary for infection are also those which stress the turfgrass-high temperatures, compacted soils, and low fertility. The disease is most severe in areas of poor drainage, heavy traffic, and soil compaction. Increase mowing height, divert traffic from affected areas, and avoid potentially abrasive grooming practices such as double-cutting, aeration, and brushing. Fertilize the turf with balanced fertilizers, especially avoiding low levels of potassium and phosphorous. Apply a systemic fungicide (Banner Maxx™, Cleary’s 3336™, Rubigan™), water in thoroughly, and follow with a separate application of chlorothalonil.

Submitted by: M. Bess Dicklow

DISCLAIMER - As always, it is the responsibility of the applicator to verify the registration status of any pesticide BEFORE applying it. Different states have different regulations as well. The author and the University of Massachusetts are not liable for any consequences of any pesticide "recommendations". Mention of any trade name is not to be considered endorsement of a product.

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