Skip to main content

Identifying Brown Patch Fungus

Brown spots in the lawn are one of the most common turf problems homeowners must deal with. What makes these spots particularly troubling is that finding what caused them can be difficult. This is because many pests and diseases produce similar looking brown patches. Yes, many have found themselves wasting precious time and energy treating for the wrong pest while symptoms continue to worsen. This is why proper identification is so important.

Perhaps the most commonly misidentified disease is Brown Patch Fungus (Rhizoctonia solani). This fungus produces distinctly circular patches of dead grass (see picture at top-right). As the grass recovers in the center, a donut-like shape often occurs. But while named for the symptom it causes, not every brown patch is an indication of Brown Patch Fungus. In fact, conditions must be just right for this particular type of fungus to remain active. Brown Patch Fungus thrives only in humid conditions at temperatures between 70 and 85°. When the weather heats up, the fungus goes dormant until favorable conditions return. Here in Central Florida, that all but guarantees dormancy June through September, since the average temperature exceeds this range. So if you’re noticing this (or a similar) pattern during these months, you may need to look elsewhere for the root of the problem, as it will nearly always be caused by another issue.

Common Causes of Brown Patches

Pets. The nitrogen found in dog waste will burn your grass, leaving irregular brown spots. Such damage tends to vary in size and location. You may need to train your pet (or your neighbor’s pet) to frequent a less conspicuous area.

Chinch Bugs. Because chinch bug damage may resemble that of Brown Patch Fungus, the key to identification is sea- son. Chinch bugs prefer the hot, dry conditions of summer...whereas Brown Patch Fungus thrives in the (relatively) cool, humid conditions of spring or fall.

Grubs. Grubs are rare when your lawn is treated preventatively, but if you’re not using Deans and begin to notice a mosaic-like pattern of dying grass, these under- ground larvae could be damaging your root system.