Brown patch is a common fungal disease in susceptible types of St. Augustine grass, especially during humid weather, according to University of Florida Extension. It most commonly occurs in the spring and fall, and risk increases with high nitrogen levels. Lawns stressed by drought, heat, pests or other disease show higher susceptibility to brown patch as well. Curing this disease proves easiest in its early stages.
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Identify brown patch in the grass early, before it spreads throughout the lawn. Look for yellowing grass that pulls easily from the stem or stolon, in addition to brown patches. In larger areas of infection, look for green grass in the center of brown patches.
Apply a fungicide to the lawn as soon as possible, treating both currently and previously affected areas for best results. Bayleton, chlorothalonil and PCNB all work well against brown patch, according to Texas A&M University Extension. Follow label instructions for the specific brand of fungicide you buy.
Conduct only minimal maintenance on your St. Augustine grass. Mow grass at a higher height of 2 to 3 inches. This adds protection for the grass and reduces stress, encouraging healthy growth. Avoid overwatering and excessive fertilization. Provide 1/2 inch to 3/4 inch of water only when grass shows signs of wilting, suggests University of Florida Extension. Limit nitrogen fertilizer applications to no more than 1 lb. per 1,000 square feet every 30 to 60 days.