An inviting green carpet of lawn is what we all strive for, so it’s a sorry day for the proud gardener when brown patches appear. What went wrong? Well, it could be that you have areas of poor drainage and standing water caused roots to rot. Or recent sodding has rooted poorly on soil that wasn’t properly aerated. Another reason could be that hard playing on part of the lawn could have compacted the soil and given grass roots nowhere to go. And don’t forget that if Fido has favorite places he uses to relieve himself, the evidence can be dead spots on the lawn.

If none of those conditions applies, then you probably have brown patch lawn disease caused by Rhizoctonia salani, a common lawn fungus. The fungus infects lawns when the temperature is cool, but only becomes visible when the temperature reaches 80 to 85 degrees and the humidity is high. The condition is uncommon in arid regions like Southern California and the Mountain States, but it’s a problem for homeowners in every other part of the country.

Calling a lawn care professional is the easiest and most sure way to deal with brown patch lawn disease, but here are the basics you should know:

How Brown Patch Disease Starts

The fungus that causes brown patch is always present in the soil, and becomes active when the grass is weak and susceptible to it. It attacks the grass at the root level and essentially kills it from the inside out. Over-watering or over-fertilizing are usually the culprits. The problem starts small, but warm weather and high humidity encourage it to grow quickly.

How to Identify Brown Patch Disease

Spotting on grass leaf blades is the first sign. These spots eventually bleed together to turn the entire leaf brown right down to the crown where it emerges from the soil. Once the infected grass starts invading the lawn, the patches are typically irregular and can be quite large. You might notice a white fungal web at the outer edge of the dead patches. Not every lawn with the fungus will look the same, because its appearance varies with the type of grass it has infected.

  • On types of grasses that should be cut short, like some Zoysias, the infestation will show as circular rings of brown patches and an expanding gray ring on the outer edge. It’s most noticeable when the grass is dewy and damp in the early morning.
  • On types of grasses that are kept taller, like St. Augustine, the fungus will often be evident as circular or nearly circular brown patches, but without a visible gray ring surrounding them.
  • On tall fescue, there won’t be the characteristic circular pattern. Instead, the disease will show up on scattered blades of grass and the whole lawn may appear to have a tannish cast.

How to Avoid Brown Patch Disease

The best way to take care of brown patch disease is to stop it before it starts. This entails keeping the grass healthy by taking care of it properly.

  • Water at the right time of day. The best time to water is early in the morning after the dew has dried. Brown patch reproduces only when grass is wet for 14 to 16 hours, so watering in the morning gives the sun time to dry the blades before the disease can propagate itself.
  • Mow to the right height. Keeping to a regular schedule of mowing promotes air circulation and permits the grass to dry more quickly after it’s been watered.
  • Don’t over-fertilize. Use moderate amounts of nitrogen fertilizer and only in the seasons recommended for your type of grass. Too much nitrogen promotes fast but weak growth.
  • Don’t over-use insecticide or herbicide. Too much can burn the grass and yellow it or turn it brown.
  • Use fungicide. If you know brown patch is a problem where you live, fungicides are effective if you apply them before you see signs of the disease.

How to Treat Brown Patch Disease

Find a fungicide that’s formulated specifically for brown patch disease and your type of lawn, and use it on the regular recommended schedule. Application won’t regrow your grass, but it will keep the fungal spores in check and let your new, good lawn care habits take effect over time. In the meantime, keep from tracking clippings from the diseased portion of the lawn to those that are still healthy and green. Don’t use the same tools on the sick and healthy parts, and avoid walking on the brown patches.

For more information on keeping your lawn healthy, check out The Lawn Institute.


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