By Bob Dailey
That’s right. The fungal plague that makes big splotches of yellow and brown in your yard is now known as “large patch” – at least here in southeast Texas. Both are caused by the same fungus (Rhizoctonia solani – try saying that quickly three times.) But there are two different strains of the fungus.
One affects cool season grasses – like Kentucky bluegrass, rye grass, fescues – none of which we should have planted in our lawns here in The Woodlands. This cool season disease is now called “Brown Patch.”
The second strain, “Large Patch”, affects St. Augustine, Bermuda, Zoysia and other warm season grasses. Large Patch usually affects grass in the winter, but most often the damage isn’t visible until spring. Somewhat circular patches that are yellow, tan or straw-brown initially are 2-3 feet in diameter, but they can grow to 10 feet or more in diameter, hence the name “large patch”. Sometimes, several Large Patch infections will grow together, causing an even bigger problem.
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.