Similar to last year in the coastal Carolina region the combination of warm days, cool nights and frequent rainfall has been textbook perfect for the development of brown patch fungal disease in turfgrass.
Favorable conditions for brown patch are high humidity, excess soil moisture and prolonged leaf moisture with warm daytime temperatures of 75 – 90 degrees and minimum nighttime temperatures above 60 degrees.
Warm weather along with high humidity set up the right conditions for disease; wet leaves, high humidity, excess fertilizer and water facilitate the spread.
Brown Patch Disease
Brown patch, one of the most damaging of turfgrass diseases, is caused by a fungus called Rhizoctonia solani. All warm season grasses are vulnerable, and so are cool season grasses like fescue and bentgrass. Warm season grasses are our concern however, because centipede, St. Augustine, Bermuda and zoysia are what we grow along the coast.
Infected grass may appear healthy until environmental conditions are right, and then the disease develops rapidly. It is visible as more or less circular-shaped thinned patches of brown or straw-colored grass which are from a few inches to several feet in diameter. The diseased patches may have a sunken brown center. You may find that the center of the patch recovers but the blighted patch continues to expand. The patches are surrounded by a dark ring, most noticeable in early morning when dew is on the grass.
The disease is not active during cold weather, but the dormant fungi overwinter in soil, plant debris and thatch. Infected turf areas are more subject to cold injury during the winter. In spring damaged spots green up more slowly than other areas of turf.
Brown patch is most closely associated with overwatering and over fertilizing. Over fertilization, excessive water, poor drainage and thatch build up all encourage development of the disease.
Irrigation should be used only to supplement rain for a total of one inch per week. Irrigate early in the morning so leaves can dry during the day.
Poor drainage should be corrected so turf absorbs more water and problem areas don’t stay wet. Depressions that hold water should be filled with top soil so those spots don’t remain soggy.
Homeowners can reduce the risk of brown patch outbreak by avoiding late season applications of high nitrogen fertilizer which stimulates growth. Brown patch seeks the tender new leaves and that in turn accelerates the fungus’ spread
Do not over fertilize. Heavy growth from too much fertilizer also increases thatch which harbors brown patch fungus. High nitrogen levels exacerbate brown patch.
Warm season grasses should not be fertilized after August. If you missed this year’s last application your grass can wait until spring. Choose a fertilizer next year with slow release nitrogen to encourage an even growth rate.
The best defense against brown patch is a properly maintained lawn. Good lawn care practices include regular mowing at the recommended height for your type of grass. Mowing too high causes thatch buildup. Don’t mow when grass is wet. Manage drainage to avoid wet areas.
It may be necessary to control brown patch with lawn fungicide. Even if symptoms are not visible the dormant fungus overwinters in thatch and soil. Fungicide is more effective when used preventively than it is after patches of disease appear.
Fungicides containing azoxystrobin are effective. The products may be applied in the spring but are better used in fall. Start treatment for brown patch in the beginning of October, sooner if you see evidence of the disease.
If you treated your turf for brown patch last year, use a different active ingredient this year. Brown patch fungi become resistant to azoxystrobin (trade name: Heritage G) when it is used alone. Alternating fungicides will prevent resistance. Select another fungicide that contains two active ingredients: azoxystrobin with propiconazole (Trade name: Headway G) or pyraclostrobin with triticonazole (Trade name: Pillar G Intrinsic Fungicide). The products are granular and need to be watered in. Always read and follow label instructions and precautions.
There are fungicides available. Read the labels before you choose.
Reach Debbie Menchek, a Clemson Master Gardener, at firstname.lastname@example.org.