April showers bring May flowers and plant diseases

By By Steve Strong / area horticulture extension agent
April 21, 2004
March 2004 was the driest on record, and so far April showers have been more scarce than usual. Still, there seems to be the typical abundance of lawn turf problems occurring like clockwork this spring, and many of them could be disease outbreaks related to all of the extra rainfall that came a year ago.
Cool night temperatures combined with high daytime humidity during spring and summer normally create ideal growing conditions for disease-causing fungi. Powdery mildew, anthracnose, and botrytis all began an early attack on dogwoods and roses this spring, joined by a gang of others making up the "10 Least Wanted List" in the landscape.
Brown patch fungus on lawn grass tops the list of turf diseases, causing homeowners more headaches than all other problems combined. Even if you don't grow flowers or vegetables, almost everybody has a small patch of grass to wiggle their toes in. And of all things, turf should be easy to grow, right?
Under normal conditions the answer is yes, but around here the weather patterns are anything but normal. Temperatures in our region can vary as much as 40 or 50 degrees in a single day, and that kind of extreme change is pretty hard on young turf just growing out of winter dormancy.
Brown patch fungus (Rhizoctonia solani) thrives during both spring and fall growing seasons, at times when the turf is most vulnerable. Brown patch can attack most any grass species, including Centipede, St. Augustine, and common Bermuda, and without treatment it tends to reoccur in areas once it has become established.
Irregular shaped, circular spots begin to form in the turf and can vary in size from a few inches to several feet in diameter. The affected areas take on a brown or grayish color, sometimes bordered by a darker smoke-colored ring. Leaves often turn yellow before dying on St. Augustine, and sometimes to a reddish color on centipede turf.
If not controlled in the early stages, brown patch and several other turf diseases can invade turf roots and kill large areas of the lawn. Repeated applications of approved turf fungicides (Terraclor, Chlorothalonil, and others) can help protect the grass until hotter drier weather naturally causes brown patch activity to decrease.
There are several factors that tend to make the grass more susceptible to brown patch fungus and other turf pathogens. Excessive applications of nitrogen fertilizer are probably the most common cause, as homeowners often try to feed the grass too early in the season before it is able to absorb the nutrients.
Wait as late as May to fertilize the lawn to prevent early fungal outbreak, and try to water only during morning hours if possible. Irrigating late in the day or in the evening hours causes the grass leaves to stay wet for prolonged periods, creating the perfect conditions for disease growth. Remembering to shut off automated irrigation systems during rainy periods can also help reduce problems.
Thatch buildup is yet another a disease promoter, and seasonal raking or de-thatching reduces the amount of decayed organic matter where turf diseases thrive. Be sure to use correct the mowing height for your specific turf grass to minimize thatch buildup, and keep the mower blade sharp for each cutting to prevent additional turf damage.
Contact your county Extension office for more information on submitting disease samples for analysis, fungicide use, soil testing, and fertilizer recommendations. Another option is visiting the MSU Web site at www.msucares.com for free publications on lawn care and pest management strategies.