Large patch disease creates large brown spots in the lawn that will increase in size as they age. When we have cooler weather combined with rain the conditions are perfect for reproduction of the spores that spread this disease. Over fertilization also works to create this problem. This is another reason why you should wait to fertilizer zoysia and bermuda grass until after it is truly green.
In the spring symptoms may look more like brown sunken areas in the yard that are not greening up. These areas can become overrun with weeds. Once temperatures rise then the desired turf will once again grow and hopefully overpower weeds. Areas that are infected will likely harbor the disease again in the fall and next year if actions are not taken to eliminate it.
When patches return in the fall they will likely have orange edges and increase in size. You may better be able to see them by standing at a distance to review the color of your lawn. Patches can reach 20 feet if they are left to develop. Cultural control practices are the best arsenal for the home owner. These include:
* Mow grass at the highest cut recommended for zoysia or bermuda grass (1.5 to 2 inches).
* Prevent roots from staying wet. Do not overwater. If your soil does not drain well then work to improve drainage and avoid soil saturation.
* Prevent a buildup of thatch. Aerate or verticut lawns during the summer and remove excess clippings from areas that have shown large patch in the past. Do not work thatch in spring or fall when the disease conditions are right for the spread of the disease.
* Do not apply nitrogen fertilizer to zoysia grass or bermudagrass in early spring. Wait until warm weather has slowed large patch development.
* Do not apply more than 1 pound of nitrogen fertilizer at one time. Do not apply fertilizer after August as this may help spread the disease.
* For areas with a known large patch problem, apply a fungicide between September 20 and October 10 before patch development. Once the disease has started to grow again, control will be ineffective until it again goes dormant. Spring applications of fungicide are not very effective.
There are no effective fungicides available for the homeowner to use. If you feel the disease cannot be controlled by cultural practices then a professional can be hired to spray in the fall. Products that can be used include Heritage, Prostar, Eagle and Insignia. Spring applications are usually not effective in preventing the disease. Mark the areas where it appears in spring and concentrate the fall spray program on those areas.
Rhizoctonia Large Patch Disease of Zoysiagrass and Bermudagrass. Stephen Vann, Gene Milus and Rick Cartwright. University of Arkansas. Extension Publication FSA7527.
The Extension office is located in Kennett, Missouri at 101 South Main Street (the old bank) on the 2nd floor. Open Monday -- Friday. University of Missouri Extension programs are open to all.
Sarah Denkler is a horticulture specialist with University of Missouri Extension
in Dunklin County.