ISSUE 6   June 8, 2006

POWDER MILDEW ON TURFGRASS

Two turfgrass samples were diagnosed by the NDSU Plant Diagnostic Lab this past week to be infected with a disease known as powdery mildew (one sample was diagnosed by phone). The organism that causes powdery mildew on turfgrass is a fungus, Erysiphe graminis f. sp. poae. The fungus initially gives the lawn a whitish appearance, as if it has been dusted with baby powder, due to the fungal mycelia and conidia (fungal spores) that are formed on the leaf surface. Affected leaves may eventually turn yellow and die. Occasionally, plants may be thinned. Powdery mildew often occurs in lawns that are covered by dense shade or have poor air circulation due to many trees, shrubs, or fences. The disease is typically favored by cool to moderate temperatures (60-72 F), humid weather, and high levels of nitrogen. However, free moisture (dew) is not necessary for the fungus to infect the grass leaves. In general, powdery mildew on turf is considered a minor disease problem, but the severity of the disease may depend on the degree of susceptibility of the host. Some Kentucky bluegrass varieties have reportedly been noticeably thinned by this disease.

The disease can sometimes be managed by improving aeration. Pruning and thinning surrounding trees and bushes can help a great deal to not only improve aeration but also to reduce pockets of humidity. The systemic fungicide propiconizole is available in a few products to help with the control of this disease (you may want to consult with a lawn care specialist in your area or your county extension agent to get current information). The fungicide may be difficult to find, it is expensive, and by itself it will not cure the problem. Fungicide treatment is a preventative measure, so for best efficacy, it is applied before symptoms develop. It will not cure already infected leaves, but if applied when symptoms appear, it might help prevent or minimize future infections during the growing season. If grass is thinned by this disease, over-seeding with a resistant variety may be needed (early fall/late summer is generally considered a good time to seed turfgrass in North Dakota).

An online version of an NDSU Extension publication on lawn diseases can be viewed at the following website:

http://www.ext.nodak.edu/extpubs/plantsci/landscap/pp950w.htm

 

PLANT DIAGNOSTIC LAB SAMPLE SUMMARY

Below is a listing of some of the samples received and diagnosed by the NDSU Plant Diagnostic Lab in the past week (not included: weed identifications, home mold identifications, seed health testing samples, research samples):

Host

Diagnosis

Ash

Ash anthracnose

Black ash

Cottony ash psyllid

Buckthorn

Rust disease (possibly oat crown rust)

Buckthorn

Rust disease (possibly oat crown rust)

Buckthorn

Rust disease (possibly oat crown rust)

Canola

Downy mildew

Chokecherry

Taphrina deformans - cherry leaf roll

Corn

Herbicide injury, sulfonyl urea type

Corn

Crusting, compaction

Elm

Possible virus infection (undetermined)

Maple

Eriophyid mite

Oak

Oak anthracnose

Potato

Growth regulator herbicide injury

Snow-on-the-mountain

Unidentified ascomycete suspected in root/crown rot Environmental stress - over-watering

Spruce

Possible herbicide injury

Spruce

Spruce spider mite

Spruce

Needleminer

Spruce

Rhizosphaera needle cast

Sugarbeet

Rhizoctonia seedling blight

Kasia Kinzer
NDSU Plant Diagnostic Lab
Website: www.ag.ndsu.nodak.edu/diaglab
e-mail: diaglab@ndsuext.nodak.edu
Telephone: 701-231-7854
206 Waldron Hall, PO Box 5012
Fargo, North Dakota 58105


NDSU Crop and Pest Report Home buttonTop of Page buttonTable of Contents buttonPrevious buttonNext button