Summer patch is a disease that can affect Kentucky bluegrass and annual bluegrass. The pathogen that causes the disease, Magnaporthe poae, is active in the late spring and summer when the roots are growing less. It is especially common on golf courses with large proportions of annual bluegrass and can also affect lawns.
Summer patch appears in warmer weather because the infection in the roots prevents the grass from surviving heat and drought. It starts out as circular or oval patches 4 to 6 inches in diameter with an orange-brown color. The patches often occur in clusters.
Once summer patch is established, the patches get larger. A patch can expand to over a foot in diameter. Most of the damage is at the leading edge of the patch. The center of a patch can get filled in with creeping bentgrass or other species. If the grass is shorter than 2 inches, the center of the dead patch can get filled in with Kentucky bluegrass.
If summer patch disease has been present for several years, the grass may have areas or rings that are damaged. Grass that has a moderate to severe level of infection will have sparse and necrotic roots.
Infection with summer patch depends on the temperature and moisture of the soil. Grass can become infected if the temperature of the soil is over 65 degrees Fahrenheit. The roots are often infected in the spring before symptoms are visible. Patches appear later during hot and dry conditions.
Summer patch survives in turf debris and root and crown tissues. It can be found in several types of soil and can be transported if soil with contaminated roots is moved, such as through aerification.
Some varieties of Kentucky bluegrass have been developed that are more resistant to summer patch. Summer patch can be avoided by planting a resistant variety of Kentucky bluegrass and following other recommendations below. Some cool-season grass species are not susceptible to the disease.
Summer patch can be suppressed by relieving stress on the grass during hot and dry conditions. This can be done through core aeration or deep tine aeration in the spring and fall to promote deeper roots. It can also be prevented by avoiding nitrogen deficiency, watering grass deeply and infrequently, syringing to cool grass on hot days, cutting grass to a height of 3 inches, and avoiding walking on affected areas.
Fungicides can also fight summer patch. Penetrant fungicides should be used because they can reach the roots. Fungicides work better if they are applied after aeration and if the grass is watered before and after application. Fungicides should be applied when the maximum daily soil temperature at a depth of 3 inches is an average of 65 degrees or higher. They will be ineffective at lower temperatures.
Fungicides should be applied several times four weeks apart, starting before symptoms are visible. Using the same class of fungicides several times can lead to other diseases that are resistant to fungicides.
Fungicides alone may not have consistent results. They work better if the other recommendations given above are also followed. Fungicides should only be used if other solutions have failed.
Watering your lawn deeply and infrequently is one of the easiest and most effective ways to prevent summer patch disease. Installing a sprinkler system can help you make sure your lawn gets the right amount of water all year long. It can be programmed to water the lawn at the optimal time of day, even if you are away. Sprinkler System Store has a selection of sprinklers and timers from top manufacturers. Look through our inventory and place your order today.
