Gray Leaf Spot Showing Up in Lawns

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Since March, we have had 28.84 inches of rain. This is 6.4 inches of rain above normal, or a 30% increase. The frequent rains have reduced the typical drought stress we see in the tall fescue lawns, but the constant moisture has increased the disease pressure.

Most lawns in Caldwell County are tall fescue (Festuca arundinacea). This is a cool season grass that grows best in the spring and fall. It grows best when temperatures are mild, between 60 and 75 degrees. Tall fescue will stay green throughout the winter, but the summers are the most stressful on it.

Tall fescue is an introduced species. It is native to the region stretching from Europe to Siberia and into North Africa. The date of the actual introduction into North America is unknown, but it began to appear in seed catalogs in 1870. By 1892, tall fescue began appearing in variety trials from Utah to Kentucky. The first tall fescue “variety” to be released was Kentucky 31, or better known now as K-31. This grass was noticed by Dr. Fergus, a professor at the University of Kentucky, in the 1931. Dr. Fergus was visiting the Suiter Farm in Eastern Kentucky when he noticed a grass that remained green all winter. He obtained seed for trials. After lengthy testing, K-31 was released as a cultivar in 1943.

In the 1950’s and 60’s, K-31 became the predominant grass in Caldwell County, as well as a large portion of the country. Since the release of K-31, there have been additional improved varieties for turf and pasture usage. New varieties are continually being tested and can be seen at field days like the NC State Turf Field Day to be held Wednesday, August 9.

For tall fescue lawns, August is when they look their worst. The July and August heat are stressful on the cool season grass. Watering from rain or irrigation helps reduce the stress, but it also creates good conditions for disease development. Moisture is a key component to disease development.

Brown patch is the main fungal disease of tall fescue lawns. This year, however, gray leaf spot has shown up in many lawns. This increase of gray leaf spot has also been noticed by Lee Butler. Lee is the NC Extension Coordinator and Director of the Turfgrass Diagnostic Lab at NC State University. He has noticed an increase of gray leaf spot across North Carolina.

Gray leaf spot initially appears as tan colored round or oval leaf spots with a dark brown border. When the leaves are wet or humidity is high, the leaf spots turn gray and fuzzy.

oval lesion on leaf

Gray leaf spot starts as an oval lesion on tall fescue leaves.

The white fluffy stuff is the fungus producing spores (disease seeds). Eventually, the leaf spots expand and cause the tip of the leaf blade to die back. In tall fescue, the disease will create orange to yellow patches from 4 to 12 inches in diameter in the lawn.

Gray leaf spot develops when temperatures are between 70°F and 95°F. The fungus also requires at least 14 hours of continuous leaf wetness for the gray leaf spot fungus to initially infect the leaf. I think this extended period of wetness is a contributing factor for why there has been such a prevalence of the disease this year.

Managing leaf wetness is an effective means for minimizing gray leaf spot. Typically, dew develops during the evening and the grass is wet until the sun dries the grass in mid morning. Watering when the grass is already wet does not cause any harm. However, watering in the late afternoon or evening extends leaf wetness and increases the chance for disease development.

To help promote leaf drying, prune or remove trees, shrubs, or other barriers to increase air movement and sunlight penetration to help dry the grass. This will help reduce turf problems. Fungicides can be applied to control gray leaf spot. Fungicide resistance to the Qol fungicides (Compass, Fame, Heritage and Insignia) has been documented. For this reason, it is necessary to rotate through multiple chemical classes when managing this disease.

Whether your lawn is suffering from gray leaf spot, brown patch, or some other ailment, September is the time to rejuvenate your lawn. Tall fescue does not spread, so overseeding is a good way to improve tall fescue lawns. When there is adequate moisture in the fall, core aerate the lawn and spread seed. Overseeding is the best way to help tall fescue spread and fill in bare spots in the lawn.

If your lawn needs overseeding, be sure to take a soil test now so the results will be back in time to make fertility corrections this fall. Stay tuned for details on how to successfully overseed your tall fescue lawn.

Written By

Photo of Seth NagySeth NagyCounty Extension Director (828) 757-1290 seth_nagy@ncsu.eduCaldwell County, North Carolina
Updated on Aug 2, 2017
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