Archive for Thursday, July 19, 2007

The Green Thumb

July 19, 2007

Since it stopped raining last week, there have been opportunities to work in the yard and garden again. But some parts of the lawn appear to be browning, as if going dormant. There are even distinct large brown spots. How can that be? We've had enough moisture, temperatures have been unseasonably mild and rabbits can't eat that much.

The condition is named just as it appears: "brown patch." It's a fungus that likes warm night temperatures and extended periods of leaf wetness. This fungus mainly affects tall fescue grasses. A dew-covered, 60-degree morning is just what it thrives on.

In severe cases, the fungus may affect the lower leaf sheaths, invade the crown of the grass and kill the plant. In most instances the grass will recover, but it may take two to three weeks.

The fungal inoculum will persist indefinitely in the soil, and there is no way to eliminate it from a lawn. It's not "carried" from one lawn to another or spread by mower tires or foot traffic. The fungus cannot be eliminated, and its appearance is generally weather-related. Outside of the weather, there are some cultural practices that can help control it.

The fungus likes extended periods of wetness, so don't water in the evening as water on the leaves will last through the night. Instead, water in the morning and allow the moisture to dry off the leaf surface as quickly as possible. Frequency, although it can cause other problems, is not nearly as important as time of day. Do not fertilize when the brown patch is active. Fungus utilizes fertilizer much faster than the grass. Limit your seeding or overseeding rates in the active areas. Seedlings are much more receptive to severe damage.

If your perfectly manicured lawn can't wait to heal, there are some fungicides that can be effective in the control of brown patch. The two most commonly used are Heritage and ProStar; neither are available in small quantities to the general public, and both are expensive. Homeowners do have access to some fairly effective products, including triadimefon (Bayer Fungus Control for Lawns and Green Light Fung-Away), propiconazole (Fertilome Liquid Systemic Fungicide) and myclobutanil (Immunox). Of the three, triadimefon may be the fungicide of choice because it protects the turf longer (three to five weeks rather than two weeks). These are for control, not elimination.

To be really effective, these need to be applied as a preventative rather than as a curative measure. A preventative program should have started in early June and must continue through August. Weekly or bi-weekly applications can get expensive and may need to be repeated year after year.

This amount of chemical application may not be advisable due to its effort, expense and effect on the environment. Proper watering, fertilization and mowing may be just as effective for a problem lasting only two to three weeks. The grass most likely will recover on its own, and we can spend more time with our rabbit issues.

-- Stan Ring is the horticulture program assistant at K-State Research and Extension--Douglas County. He can be reached at 843-7058 or Sring1@.ksu.edu.

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