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Healthy lawn is best defense against summer turf diseases

June 19, 2009 12:36 am

TURF DISEASES CAN do anything from affecting the appearance of your lawn to wiping out large parts of it. Managing and preventing turf diseases involves a combination of practices that include maintaining a turf stand capable of fighting off disease and using pesticides when needed.

Any turf management plan must begin with proper identification of diseases. Many problems caused by humans and pets can be confused with diseases and complicate the initial diagnosis. Such issues include chemical burns from fertilizer and pesticides, dog spots caused by urine and dull mower blades.

There are many of environmental and manmade conditions that contribute to the development of summer fungal diseases. Prolonged leaf wetness and high humidity provide ideal conditions for the fungi to grow.

We contribute to this problem by watering our turf too frequently and at the wrong time of the day. The best time to water lawns is between 4 and 8 a.m., as this allows the leaves to dry during the day and prevents the fungi from getting a start. Deep, infrequent waterings--once or twice a week--are best.

Poorly drained soils contribute to the occurrence of fungal diseases. Improve drainage by aerating the lawn to reduce compaction and let more water soak in.

Heavy spring nitrogen applications can contribute to the development of brown patch, leaf spot and other diseases. Limit or better yet eliminate the use of nitrogen fertilizers in spring. Follow a fall fertilization program for fescue and other cool-season lawns that are most common in the Fredericksburg area.

Poorly balanced soil fertility is another cause of brown patch and other diseases. Get a soil test to learn how much fertilizer and lime should be applied, preferably in the fall, to keep soil pH and phosphorous and potassium levels balanced.

Daytime and nighttime temperatures can also aid fungal growth. Many of these diseases do well when daytime temperatures are between 60 and 90 degrees and evening temperatures drop to the 50- to 65-degree range.

Improper mowing can also encourage turf disease development. Grass cut with a dull blade will have a ragged edge, providing an entry point for diseases. Keep your mower blade sharp and mow cool season lawns to a height of 2.5 to 3 inches.

The symptoms of many fungal diseases are similar, which makes identification difficult. When viewed from a distance, several lawn diseases will have circular spots that can range in size from a few inches to several feet in diameter. Others will be irregularly shaped patches of various sizes. The grass affected by the disease will have different color patterns; a dollar spot is usually bleached white, summer patch is straw yellow and others will be brown or gray.

Take a close look at individual blades of grass. The leaf color is caused by lesions on the grass blades, and the shape and color of the lesion helps identify the disease.

With dollar spot, the grass blades will have hourglass lesions that are bleached in the center and have tan to red-brown margins. The leaves of brown patch will have lesions with dark-brown margins. With summer patch the leaves will be grayish-green to yellow to straw-colored. Leaf spot is characterized by dark, water-soaked spots or lesions on the grass blades.

The fungal mycelium (thread-like structures) also help with identification. When dew is present, a cottony-like web is often visible in the patches affected by dollar spot. Dark-brown mycelia may be found on the roots when summer patch is present. On cool, wet days, red threads can protrude from the leaf tips when red thread is the disease.

To correct a plant disease problem, homeowners may need to combine changes in maintenance with the proper use of the correct pesticide. Virginia Cooperative Extension Agents can help with identification, recommend pesticides and offer tips that will help eliminate the disease and prevent it from recurring.