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University of Missouri Extension
Published: Monday, Sept. 16, 2013
Gerald "Lee" Miller, 573-882-5623
COLUMBIA, Mo. – Keeping lawns disease-free is often a combination of scientific research and good management practices.
University of Missouri Extension researchers are always searching for better ways to control large patch, which infects zoysia lawns, and brown patch, a problem for tall fescue lawns.
“For brown patch we are investigating new granular fungicides, comparing them to liquid sprays,” said Lee Miller, assistant professor of plant sciences for University of Missouri Extension. “For large patch, we have control trials looking at products that are more environmentally sensitive.”
Miller said they also research different strategies for disease control such as application timing and post-application irrigation. He said their goal is a better understanding of the life cycle of the pathogen. If they can interrupt that life cycle at the right time, then they could reduce fungicide rates or lower the number of applications necessary for control.
Another study looks at fertilizer and the effect of the nitrogen source on the large patch pathogen. In preliminary lab trials, they found that the large patch pathogen grown on an ammonium-based medium couldn’t create the pigment melanin. This pigment plays a role in the infection process of other important plant diseases.
The next step is testing ammonium-based fertilizer in the greenhouse and in the field to see if melanin suppression works outside the lab.
“This research is at the very beginning and we have no applicable results yet,” Miller said. “We’ve been working on this for only a few months, so it’s going to take time to learn whether this can be applied as a sustainable management strategy.”
Zoysiagrass diversity is another problem. Currently, the only cultivar used in Missouri is Meyer. Miller says they are testing additional cultivars, looking for varieties that are less susceptible to large patch.
“Meyer has been the go-to grass for 30 to 40 years in Missouri because of its cold tolerance. Unfortunately, Meyer is very susceptible to large patch,” Miller said. “We have planted 35 new zoysia cultivars at South Farm, as part of the National Turf Grass Evaluation Program, and we’ll be evaluating their inherent resistance to large patch.”
Future research aside, homeowners can reduce large patch by using good management practices now. This is particularly true of properly timing fertilizer applications. Fertilizer should be added when temperatures are most favorable for plant growth. Knowing which lawn grass species you have will determine the correct time to add fertilizer.
If you have zoysia, a warm-season grass, May through August are appropriate months for adding fertilizer, Miller said. Don’t apply fertilizer in zoysia in the fall or you may predispose your lawn to large patch infection.
Tall fescue, the species used in most Missouri lawns, is a cool-season grass and therefore calls for the opposite approach.
“For tall fescue, September-October is the time that you need to concentrate on fertilizing, seeding and weed control,” Miller said. “If you add nitrogen fertilizer to tall fescue in the late spring/summer, you’ll greatly enhance your chances of getting severe brown patch.”
In addition to fertilizer timing, proper watering is also important. Both large patch and brown patch need free moisture to grow, and the more moisture they get, the more actively these diseases spread, Miller said. Homeowners with in-ground irrigation systems tend to overwater and can actually bring the disease on themselves, he said.
Plant diseases are opportunists, taking advantage of plants that are stressed. Miller says keeping your lawn healthy by following good management principles is the best defense against large patch and brown patch pathogens.
For more information, see the MU Extension publication “Identification and Management of Turfgrass Diseases” (IPM1029), available for free download at extension.missouri.edu/p/IPM1029. You can directly access the section on brown patch at extension.missouri.edu/p/IPM1029-5 and on large patch at extension.missouri.edu/p/IPM1029-13.
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