Controlling Frogeye Disease in Lawns

Q. Can you tell me why lawn grass gets frog eyes and the best way to prevent it? Also why does some of the grass look so yellow?

Summer patch, frequently called frog-eye or frogeye patch.

A. This is the time of year we usually see frogeye disease, or Summer Patch, in lawns. This used to be called Fusarium many years ago, but no longer. The yellowing may be due to a lack of nitrogen or iron fertilizer or both.

This disease is a hot weather disease on tall fescue in the Mojave Desert. It occurs when air humidity increases in the summer months or if we water our lawns early in the evenings.

Consider the disease organism to be present on all tall fescue lawns. The symptoms of the disease appear during hot, humid weather or during a rainy period. The worst scenario is if it rains in the afternoon or early evening and keeps the lawn wet during the night.

If our lawns stay wet for at least six hours at night in July and August, this tends to promote this particular disease. The disease will take about 3 to 4 days to appear when conditions are right.

Apply a preventive fungicide if your lawn has been susceptible to this disease in the past. If it has, you need to plan that it will happen again. Purchase a lawn fungicide that prevents frogeye disease, a.k.a. Fusarium or summer patch and states so on the label.

Apply it to susceptible areas 2 to 3 days after summer rains occur. Follow label directions for reapplication of the fungicide. Lawn fungicides aimed primarily at disease prevention and seldom cure diseases once they start.

Fungicides will stop a disease from spreading once applied but seldom cure it.

Nonchemical control includes aerification of the lawn in spring or fall months. Increase the mowing height or make sure lawns are mowed at 2 1/2 inches or higher. Make sure the irrigation has head-to-head coverage and prevent it from getting water stressed during the heat.

Use organic fertilizers on the lawn including composts and bagged manure products. Compost applied as a fertilizer has been shown to reduce many lawn diseases. Compost should be applied monthly during the growing season. Use mulching mowers and leave the mulched clippings to decompose in the lawn and on top of the soil.
Those of you living in Las Vegas can get compost for top dressing lawns in bulk at Viragrow.
Viragrow website