Preventing Lawn Diseases

Posted 3/24/19

The excess rainfall while being good for growing grass, has led to some problems in home lawns. Lawn diseases, especially those caused by fungi, are expected to be very common this year in and around …

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Preventing Lawn Diseases


The excess rainfall while being good for growing grass, has led to some problems in home lawns. Lawn diseases, especially those caused by fungi, are expected to be very common this year in and around our county. One of the most common of these turfgrass diseases is called “Brown Patch”. Excessive nitrogen fertilizer and thatch buildup often lead to outbreaks of brown patch on centipede, zoysia, St. Augustine, and other grasses. The disease usually develops on lawns during periods of wet, overcast weather in the late spring, especially if temperatures are in the upper 70’s to the mid 80’s. 

Brown patch first appears in lawns as small circular patterns several inches in diameter and expanding rapidly to three to six feet in diameter. Higher cut grasses such as Centipede and St. Augustine appear to wilt and soon collapse giving the diseased area a sunken appearance. The damaged turf will usually recover starting with green grass growing from the center of the spot. The worst problem is that in the meantime weeds can invade the diseased areas.

In order to help prevent brown patch, first reduce the amount of nitrogen fertilizer that you apply. It is better to apply small amounts of fertilizer more often than to apply large amounts all at one time. Time release fertilizers are also beneficial in reducing your chance of a brown patch outbreak. Also maintain adequate phosphorous and potassium levels in the soil to maintain the health of the grass. Periodic early spring dethatching can also help since the thatch layer harbors the fungus that causes brown patch. Improved drainage is essential for brown patch control. Pruning nearby trees and shrubs can help the grass dry faster and improve air flow. There are also many fungicides labeled for controlling brown patch. Make applications according to directions beginning at the first sign of the disease or else when weather conditions favor the disease (like now). Apply the fungicides at recommended rates and always according to the directions on the label. Note that areas of turf that are affected by brown patch tend to have reoccurring problems. I would also plan to make an application of fungicide in the early fall around September to problematic areas.

Slime mold is another fungal disease problem that I have seen quite a bit. It is very common in our area on just about any turfgrass that you happen to grow. Centipede grass, however, seems to be one of its favorites. The most obvious sign of slime mold outbreaks is the gray to black crusting of the grass blades caused by the fungus fruiting bodies. At times the fruit bodies release spores that look like a dark gray dust cloud, especially if you walk across the area or run over it with a mower. The affected areas also look like they have an oily appearance. Slime molds for some reason seem to affect the same area of yard year after year at about the same time of the year. Here’s the good news… if you are going to have a turf grass disease in your lawn slime mold is the best one to have. Do not waste any money buying fungicides or other sprays for slime mold. Mowing or light raking are effective means of destroying the crusty fruiting bodies of slime molds. Since slime molds may be more common on heavily thatched or poorly drained portions of a lawn, renovation of the affected areas should reduce the incidence of the disease.

Many diseases have also popped up in gardens and landscapes as well. One rather severe disease called “late blight” is predicted to be a problem this growing season in tomatoes. This disease can affect other crops such as potatoes, peppers, eggplant, and several others. We do not see this disease every year fortunately; however, weather conditions have been just right for it to pop up. The main problem with this disease is that it spreads rapidly and can take out a stand of tomatoes or other vegetables in a matter of days. This disease usually starts off with dark colored spots on the foliage and usually the stems as well. The fruit often looks dark purplish to black and oily in appearance starting at the stem end and eventually covering the entire fruit. There are some fungicides which can help with this disease such as chlorothalonil which is sold under various trade names as well as several other fungicide products. Just make sure to read and follow the label of the product you select. The best control for late blight; however, is some warmer drier weather. Due to the rapid spread of this disease, you should plan to make a fungicide application at the very first signs of the disease.

Early blight is another disease (completely different than late blight) that effects about the same crops as does late blight. Although not as serious a problem, early blight usually starts at the bottom (older growth) of the plant and is marked by yellowing of the foliage often with black spots that have a concentric ring or “bulls eye” appearance on close inspection. Because it starts at the bottom of the plant and usually works its way up, I often hear the comment that “my tomatoes are firing up”. Again we have had good weather conditions for early blight as well. The same fungicides that are recommended for late blight will also work as a protective spray for early blight as well. I also recommend a good mulch layer such as pine straw to give the plants a barrier from the soil. Staking or caging your tomatoes and increasing the plant spacing to increase sunlight and air flow can help the foliage to dry better and can help reduce problems with diseases.

Not even landscape plants have been spared. I have had several azalea leaf gall samples brought into the office. Azalea leaf gall is marked by thickening leathery appearance of your azalea’s foliage. It usually begins as light greenish or white and will eventually turn black. Fortunately this is not a severe problem and the best answer is to simply prune out the galls and remove them from the area where your azaleas are growing. It is time to prune your azaleas anyway so take a little extra time and simply remove the galls as you find them.