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Fixing a patchy lawn

Wayne Hobbs
Posted 12/7/16

GREEN COVE SPRINGS – After a long and hot summer, turf grass in Northeast Florida has been through a lot of stress. It has baked in the sun, been through weeks without rain, and at times cut too …

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Fixing a patchy lawn


Posted

GREEN COVE SPRINGS – After a long and hot summer, turf grass in Northeast Florida has been through a lot of stress. It has baked in the sun, been through weeks without rain, and at times cut too short, irrigated too much or too little, and been covered with pesticides, herbicides and fertilizers.

However, as fall begins the grass begins to go dormant, the insects hopefully do so as well, and the turf can get a break but some diseases can begin to thrive. Probably the most common of these fall diseases is brown patch (Rhizoctonia solani), also known as large patch, which can cause large areas of the turf to yellow, then turn brown, and finally die. This disease can infect all warm-season turfgrasses including St. Augustine grass, Bermudagrass, Zoysiagrass, Centipedegrass and Bahiagrass.

Brown patch becomes active in lawns when temperatures drop below 80 degrees Fahrenheit and become dormant at temperatures above 90 degrees Fahrenheit. Infection often occurs during periods of high humidity or excessive moisture for 48 hours of more and is spurred on by excessive thatch and the use of high rates of nitrogen fertilizer, normally more than 1.1 pounds per 1,000 square feet.

The symptoms of this ailment start as 6-12 inch off-color patches that turn yellow, then reddish brown, then brown to straw colored. The outer ring of the patch will be dark and wilted and this is the location where the pathogen is actively damaging new turf as the ring expands. Looking closely, you will also see black rot at the point where the grass stem meets the leaf blade.

If brown patch is present in your lawn, there are some things you can do to prevent it from reoccurring the following year. Avoiding excess soluble nitrogen fertilizers from November-April can help. Use slow release nitrogen fertilizers with an equal amount of slow release potassium. In fact, avoid fertilizing from October to February because turfgrass is dormant and will not need the nutrition during this time.

It is also best to never stress the lawn by mowing it too short, with St. Augustine grass the height should be 3-4 inches and never cut more than 1/3 of the leaf blade each time you mow. Also, lawn mowers can spread the disease so mow diseased areas last and wash the clippings off of the mower when done.

Irrigation or watering should also be limited to one day a week following daylight savings time and make sure the follow the St. Johns River Water Management District watering guidelines all year. If you feel that your lawn stays wet a day or two following irrigation, you will want to water for less time and do not water if there is a rain event.

The best strategy is to only water when the grass is showing signs of wilt and water in the early morning. You may also find this disease in areas that have shade, especially in the morning, which can lead to turfgrass staying wet longer than in sunny areas.

Another strategy to consider is to use preventative fungicides. This is done by monitoring the timing and location where the disease normally occurs each year and then apply a fungicide by the instructions given on the label before conditions become right for the growth of brown patch. Commonly recommended fungicides are propiconazole, thiophanate methyl, mycobutanil or azoxystrobin.

If patches are large and the turfgrass does not recover, re-seeding, plugging or re-sodding may be needed. Following the establishment period, cultural practices as described in this article should be followed to limit the chance of the disease returning.

If you have any more questions about turfgrass, any other landscape topics, or need plant or pest materials identified, contact the University of Florida/IFAS Extension Office online at http://www.clay.ifas.ufl.edu, follow us on Facebook, or call by phone at (904) 284-6355.