Heavy rains bring fungus, diseases to your lawn

Q. There is a fungus running rapid in my lawn after all the rain that appears to be killing a well-established lawn. Any advice you can give to deal with this fungus? Will it die when it stops raining and gets hot? Is it too late to deal with it?

A. Three main types of fungus and disease cause these problems. The first is a general group known as “water molds,” which are diseases known scientifically as Pythium and Phytophthora species. Both of these diseases produce mobile spores that can swim through the water and attack the roots of lawn plants as well as annuals and vegetable plants. These diseases cause what is commonly known as damping-off and root rot. Usually when these diseases attack, you will notice reddish to brown lesions just below the green part of the leaves. Then the entire plant wilts. The plant can be pulled easily out of the soil as the roots are slimy. These plants are dead and you will have to reseed in September with resistant varieties.

The second group consists of slime molds and they will not kill the lawn but live on any sugar found on the leaves. They can be bright yellow, red, orange or and white. They can be found in any excess rainy conditions. These organisms can move, so biologists have a hard time trying to classify them as either an animal or a plant. Usually heavy downpours of rain will cause them to break up and they will disappear.

The third group consists of two main fungi groups —Dollar Spot (Sclerotinia homoeocarpa) and Brown Patch (Rhizoctonia solani). Dollar spot turns grass to light brown in circular areas about the size of a silver dollar to 6 inches in diameter. This begins in rainy weather in May and June.

In the early morning, you will notice a white cob webgrowth with the dew. This disease can reappear in September and October if the rainy season returns. These circular spots can grow together and form large dead areas. This disease can spread by spores being carried on shoes and mowing equipment.

The lawn can recover from this disease if the weather conditions are favorable for grass growth. Usually the turfgrass was lacking nitrogen, so in the fall you may want to apply turf fertilizer containing nitrogen. This disease can be prevented by an application of a general lawn disease control applied in the spring as the grass begins to grow and another application in the fall. If you notice this disease spreading, you will need to apply every 10 days.

Brown Patch shows up with a dark smoky purple color at the edge of the disease. You will be able to pull out the blades of grass very easily from the base of the plant. Again a white tuft will appear on the blades of the newly affected grass in the early morning. After two to three weeks, the grass will turn brown in the center of the attacks. After two to three weeks, the center may try to turn green again giving a doughnut shape.

If the weather turns hot, the turfgrass will usually die. This disease is caused by too much nitrogen fertilizer being applied to the plant in early spring. You can treat this Brown Patch with a general lawn disease preventer at least three times for every 10 days. If the grass does not grow in the fall, you can plant varieties — Birdie, Citation, Derby, Diplomat, Omega, Pennfine or Yorktown II, which are resistant to this disease.

This story was originally published July 2, 2015 at 7:50 AM with the headline "Heavy rains bring fungus, diseases to your lawn."