Large Patch will infect the grass in the fall and winter when soil temperatures go below 70°F, but it usually doesn’t become evident until things warm up again in the spring.
This disease is caused by excess nitrogen (too much fertilizer), poor soil drainage (compacted soil), closely mown grass and, of course, over-irrigation. Taking care of these four problems will go a long way toward preventing Large Patch.
If you do recognize Large Patch in the lawn before spring, it’s probably best to do nothing until the grass starts to green up. If remedying the situations above haven’t worked, there are organic methods to slowing and eliminating most of the infection. Copper bonide, and several bacteriologic strains may help.
However, remember that Large Patch is forever present in the soil. Improper soil and lawn practices - cutting grass too short, overirrigating the lawn, applying too much fertilizers and poor soil drainage are prime reasons for fungal attacks on the lawn. Planting winter rye is another reason. Warm season grasses need one inch or less of water per week to thrive. If it rains, then it needs even less. And warm season grasses are dormant and turn yellow in the winter, so they usually don’t need to be watered at all.
If you do suspect you have Large Patch, the best thing to do it to have it identified by an expert. Michael Potter, the Montgomery County horticulture agent for the Texas A&M Agrilife Extension Service (9020 Airport Road, Conroe) is a turf grass specialist and can diagnose the problem.