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Senior Information Specialist, West Central Region
University of Missouri Cooperative Media Group
Published: Thursday, May 15, 2008
Travis Harper, 660-885-5556
BLUE SPRINGS, Mo. - Adequate soil moisture and warmer weather are making lawns grow a little faster than most people probably would like them to right now. "Just because lawns are doing well now does not mean the grass will continue to be healthy," cautioned a University of Missouri Extension agronomy specialist.
As the season progresses, turfgrass diseases will begin to appear. "Homeowners often neglect to manage these diseases until they become visible and then try to make a rapid diagnosis and apply a fungicide," said Travis Harper. "In some instances it may be too late. Maintaining a healthy, disease-free lawn should begin right now."
The first step in maintaining a healthy lawn is proper soil fertilization. Soils with low nitrogen levels increase the susceptibility of turfgrass to diseases such as dollar spot and red thread. On the other hand, too much nitrogen makes cool-season grasses more vulnerable to leaf spot, Rhizoctonia brown patch and Pythium blight. Low pH is often associated with diseases such as brown patch as well.
Low potassium levels in the soil reduce turfgrass tolerance to high temperatures and drought stress, which can increase the potential for diseases such as summer patch.
How do you know for sure whether your pH and nutrient levels are too high or too low? Have your soil tested at your local MU Extension center.
Mowing height and frequency also affect the likelihood of turfgrass diseases. Optimal cutting heights for cool-season grasses range from 2.5 to 4 inches, depending on the grass species. Warm-season grasses can range between 1 and 2 inches. Cutting grass lower than these recommended ranges increases the likelihood of disease.
To determine how often to cut, use the "one-third rule" of mowing: Remove no more than one-third of the leaf growth during a single mowing. "Mowing creates wounds on the grass blades through which fungi can enter," said Harper. "Make sure to keep your mower blades sharp. Leaf cuts made by a sharp mower blade are cleaner and heal faster than the tearing and shredding caused by a dull mower blade."
Overwatered lawns are more likely to develop turfgrass diseases. Water lawns only when they show signs of needing water. Allow cool-season grasses to have periods of drying (near wilting) to disrupt the growth cycle of fungi favored by excess water. Lawns should be watered only in the early-morning hours. Lawns watered in the evening remain wet throughout the night, which encourages the development of diseases.
Even if all of these techniques are followed, development of turfgrass diseases may be unavoidable. "This does not necessarily mean that a fungicide needs to be applied," said Harper. "Grasses can naturally recover from some diseases when environmental conditions favor growth of the turfgrass." In some situations, however, it may be necessary to use a fungicide to suppress diseases until favorable environmental conditions return.
The regular use of these cultural practices, along with the occasional use of fungicides, will help your lawn stay healthy all year long.
MU Extension guide "Turfgrass Disease Control" (G6756) is available online at http://extension.missouri.edu/explore/agguides/hort/g06756.htm.
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