By: Young-Ki Jo, Assistant Professor and Extension Specialist
Large patch affects most warm-season turfgrasses growing in Texas including:
- buffalograss (Buchloё dactyloides)
- bermudagrass (Cynodon spp.)
- centipedegrass (Eremochloa ophiuroides)
- St. Augustinegrass (Stenotaphrum secundatum)
- Zoysiagrass (Zoysia spp.)
Particularly, large patch is the most chronic and economically important disease of both St. Augustinegrass and zoysiagrass in Texas (Figures 1 and 2). This same fungus also causes brown patch in cool-season turfgrasses.
The fungus is present in the soil and thatch layer year-round, but the disease only occurs under certain conditions. The fungus survives in summer heat, but thrives in cooler temperatures when the soil is wet. The disease occurs when temperature is below 70 degrees Fahrenheit. The fungus spreads in the thatch layer and infects the grass’s sheaths, stolons and roots. It is especially severe in turfgrass that is poorly drained and over-fertilized.
The first symptom of large patch is circular, discolored patches on the turf. The outer borders of the patches are orange or yellow; the orange leaves are newly infected and starting to die. Diseased shoots pull easily from the sheath where they attach to the stolons. This is a practical method for diagnosing large patch in the field. Diseased stems and sheaths show dark brown lesions (Figure 3).
Grass will recover from light disease symptoms as temperatures begin to rise in the late spring; new growth will fill in the patches during the summer. However, grass may not recover when the disease causes extensive crown and root damage. In these cases, it is often necessary to resod the damaged area.
The following conditions promote large patch infection:
- Over-fertilization late in the fall
- Locations with poor drainage
- Low mowing height
- Excess thatch
Control and management
Large patch is hard to get rid of once the disease has been established and the disease recurs under certain environmental conditions every year. Therefore, preventing large patch is critical. Proper fertilization is an excellent way to avoid outbreaks of large patch. The ideal time to apply fertilizer is 6 weeks before the first frost and 3 weeks after green-up.
It also helps to improve drainage in areas that hold water or stay saturated for long periods. Water evenly and only when necessary.
Mowing turfgrass to appropriate heights will discourage the disease. The proper mowing heights are 2–3 inches for St. Augustinegrass and 1–2 inches for zoysiagrass.
Core aeration, raking and vertical mowing will decrease thatch, which favors plant health growth and discourages disease development.
In summary, the following cultural practices will help to prevent large patch:
- Remove thatch
- Reduce leaf wetness periods
- Ensure good soil drainage
- Water early in the morning
- Balance nitrogen fertility
- Maintain the proper mowing height
- Balance the fertility level
St. Augustinegrass and zoysiagrass are very susceptible to large patch. To ensure turf quality, you may need a fungicide application. The best protection by fungicides can be achieved when they are applied before disease symptoms appear. The best time to apply fungicides is when the soil temperature drops below 70 degrees Fahrenheit in the fall, before symptom development. Fungicide efficacy is limited once the disease symptoms have been occurred. Damaged grass will not recover until the following spring. Fungicide applications in the spring are not cost-effective.
There are many fungicides (Table 1) that control large patch effectively, but the key to successful fungicide programs in to treat turfgrass before or immediately after the disease begins in the fall (October to November) in Texas.
Download a printer-friendly version of this publication: How to Diagnose and Manage Large Patch Disease in Warm-Season Turfgrass
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