Lawn Disease Questions Answered

By Jaime Staufenbeil - Milorganite Agronomist
August 8, 2020

Lawn Diseases Accompany Summer Heat and Humidity

Many of us have had more time to pay attention to our lawns these past few months. We may not have more time to work in our yards, but because we’re home more we notice things that previously may have gone unnoticed or simply ignored.

There’s no break in sight for the heat and humidity we’re experiencing throughout most of the country. Two lawn diseases that we’ve been getting a lot of customer questions about are dollar spot and brown patch, both are lawn diseases that thrive in this weather.

Dollar Spot

Dollar spot is a fungus affecting both cool-season (Bluegrass and Ryegrass) and warm-season (Bermudagrass, Centipedegrass, and Zoysiagrass) grass varieties. It flourishes in both drought conditions, as well as when grass blades are wet for a prolonged period of time.

Cool-season grass varieties are susceptible to dollar spot between late-March and early-November—essentially the entire growing season. Look for dollar spot on warm-season grass varieties  May through September.

Dollar spot causes straw-colored patches in the lawn that are 2 to 6 inches in diameter. The grass blades will have hourglass-shaped lesions with reddish-brown margins. In the morning dew, the patch may look as though it’s covered in spider webs. This is the branching mycelium of the dollar spot fungus. The mycelium “disappears” when the dew dries.

Proper fertilization and watering can help manage dollar spot.

dollar spot lawn disease

Nitrogen-poor soils contribute to the spread of dollar spot. Maintaining an annual fertilization schedule using a slow-release fertilizer, such as Milorganite, will help to restore depleted nitrogen.

Lawns generally need 1” of rain or irrigation every week. Watering deeply and infrequently is most effective. Short sprinkles from a hose promote shallow root growth and weakens grass. Watering early in the day, 4 a.m.–10 a.m., allows the grass to dry more quickly than watering in the evening.

Dollar spot is spread through infested leaf blades. Mow unaffected areas before moving on to areas with dollar spot. Rake up grass clippings and dispose of in the trash. Rinse and dry mower blades afterward mowing. These steps can help to prevent unintentionally spreading the disease.

Fungicide is rarely necessary to control dollar spot.

Brown Patch

Many of our customers’ lawns have been affected by another fungus this summer: brown patch this summer, which survives in thatch and other debris, awaiting to take advantage of the next period of hot, humid weather.

Brown patch thrives in hot, humid weather, generally when evening temperature are above 65 F, and where there’s an excess of nitrogen in the soil. It results in poor-quality turf and causes grass blades to turn dark and wilted, and die quickly.

All warm-season grass varieties are susceptible to brown patch, particularly St. Augustinegrass and Zoysiagrass, November through May. Cool-season grass varieties, especially Bluegrass, Fescue and Ryegrass, are susceptible mid-June through early-September.

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Brown patch, not surprisingly, causes large patches of lawn to turn brownish-tan of up to 3 feet in diameter on cool-season grasses during hot, humid weather. Often times you can see a dark purple-ish grey “smoke ring” around the border of the diseased area. On warm-season grasses, patches can reach up to 20 feet in diameter during cool, wet weather, generally in spring or fall.

To manage brown patch, do not apply excess nitrogen to your lawn, especially from quick-release or soluble, liquid fertilizers. Be sure to aerate your lawn to avoid soil compaction. If a certain area of the lawn get the disease regularly, make sure there is good air circulation in the area and adequate sunlight To help prevent over-fertilization, have your soil testing to identify what nutrients are lacking in the soil. In the case of these two diseases, one low N can contribute to the disease while the other can be caused by high N.  It’s not a bad idea to have the soil tested by a university every 3-5 years just to better understand where your nutrient levels are at especially if you have reoccurring disease issues. Stick to an annual fertilization schedule using a low-nitrogen, slow-release fertilizer such as Milorganite, which provides nutrients at a rate plants need.  

Water deeply and infrequently early in the day to allow grass blades to dry out.

Mow affected areas last, and gather and dispose of the clippings in the trash to help prevent the disease from spreading. When finished, rinse and dry the mower blades. Reducing thatch to increase air circulation will also help.

Lawns damaged by brown patch usually recover when more favorable growing conditions return.

Fungicides are rarely needed to treat brown patch.

Can I apply Milorganite during hot weather?

Customers often call for reassurance that Milorganite really can be applied during hot weather. The answer is, “Yes!” That’s because Milorganite is a non-burning, slow-release fertilizer that doesn’t need to be watered in. Nutrients are only available to plants when there’s enough moisture. Please note: no amount of any fertilizer will ever bring a lawn out of heat stress or dormancy.

Insect Damage

Insect damage to lawns has been increasing the past several years, resulting in more customers asking for help in identifying insects and management options. We recommend contacting your local Extension office for assistance from experts in your area.

The extended forecast of hot, humid weather for much of the country will continue to provide ideal conditions for many lawn diseases to flourish. Continue to monitor for lawn diseases throughout summer. If patches of your lawn are damaged by a disease, don’t forget to add “repairing damaged patches of lawn” to your list of fall yard and garden activities.