Lawn maintenance for the year is not over yet.
Recent Coastal Carolina weather has been textbook perfect for the development of brown patch and large patch fungal disease in turfgrass.
The highly destructive disease grows most rapidly when daytime temperatures are between 80 and 85 degrees, night time temperatures are above 65 degrees and the humidity is high. Brown patch and large patch are caused by two strains of a fungus called Rhizoctonia solani.
Favorable conditions for brown patch and large patch turf disease development—high humidity, excess soil moisture, prolonged leaf moisture—can occur in spring and fall, generally during warm daytime temperatures 75 – 90 degrees and minimum nighttime temperatures above 60 degrees.
Brown Patch and Large Patch Disease
Rhizoctonia solani fungi cause the most damaging of turfgrass diseases. All warm season grasses are vulnerable, so are cool season grasses like fescue and bentgrass. Infected grass may appear healthy until environmental conditions are right, and then the disease develops rapidly.
Disease is visible as thinned patches of brown or straw-colored grass which are generally round in shape, from a few inches to several feet in diameter. You may find that the center of the patch recovers but the blighted patch continues grow. 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; and infected turf areas are more subject to cold damage.
The best defense against brown patch and large patch is a properly maintained lawn. Over fertilization, excessive water, poor drainage and thatch build up all encourage the development of the disease. Brown patch and large patch are most closely associated with overwatering and over fertilizing.
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.
Do not over fertilize. High nitrogen levels exacerbate the disease. Too much nitrogen increases the buildup of thatch which leads to disease problems. Nitrogen fertilizer should be slow release. Warm season grasses should not be fertilized after August.
Good lawn care practices include regular mowing at the recommended height for your type of grass. Mowing too high causes thatch buildup. Mow only when the grass is dry.
It may be necessary to control brown patch and large 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 most effective when used in fall. Brown and large patch fungi become resistant to Azoxystrobin (trade name: Heritage G) when it is used alone. Consequently, it should be alternated with 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 all label instructions.
Start treatment for brown patch and large patch in the beginning of October.
Be aware centipede is sensitive to herbicides, especially those that contain 2, 4-D. Carefully select the preemergent you use on your turf. Many contain herbicides that inhibit cenitpede’s ability to recover from injury. Always read the label on preemergent to be sure it is safe for use on your type of grass. Do not apply it to areas where grass is dead or dying. Avoid weed and feed products because they often contain herbicides that are damaging to centipede.
There is no benefit to over seeding warm season turf with rye grass for the winter. Rye uses nutrients in the soil that your turf grass will need for green up next spring. Fertilizing the rye can stimulate growth in your warm season grass and result in winter damage. When rye grows on centipede it holds in moisture which can cause disease in the centipede. Zoysia grows too thick for rye to penetrate and germinate. Bermuda is the only warm season grass that can tolerate the stress from over seeding.
Reach Debbie Menchek, a Clemson Master Gardener, at email@example.com.