Large Patch

Ned Tisserat 
Extension Specialist, Plant Pathology

Symptoms

Large patch symptoms may occur anytime during the growing season, but they are most common in spring and fall as zoysiagrass enters or breaks winter dormancy. As its name implies, the disease results in the formation of large patches of blighted turf that may exceed 20 feet in diameter. The disease occurs on both residential lawns and golf courses, but it is more severe when the grass is mowed to heights of less than one inch (i.e. golf course fairways) and where soil drainage is poor.

Circular, slightly matted areas of straw-yellow zoysiagrass initially develop in late September to early October during cool, rainy weather (Figure 1).  Leaf blades, particularly those near the patch margin, may develop a yellow-orange color. Individual shoots within the patch exhibit reddish-brown to black lesions at the base of leaf sheaths (Figure 2).  Lesions normally do not develop on the leaves. Depending on disease severity, unaffected, living shoots may be scattered throughout the patch.

Figure 1.  Large patch symptoms on zoysiagrass in fall.

Figure 2. Lesions on lower leaf sheaths of zoysiagrass.

During favorable weather, the disease progressively kills more shoots, resulting in large, blighted patches of turfgrass with bright orange margins. Crown infection may continue into November long as soil temperatures remain above 50 degrees F and soil moisture is high. Patch enlargement after fall dormancy (October) may not be noticed until zoysiagrass resumes spring growth.

Patches of zoysiagrass damaged by large patch reappear in spring as light brown, sunken areas that are slower to recover from dormancy than surrounding, healthy turfgrass (Figure 3). Leaf sheath lesions typically are not present in early spring, but sheath rotting may resume in April and May as soil and air temperatures increase. This can result in patch expansion and symptoms similar to those described for fall infection (Figure 4). New patches also may develop in spring. (Figure 5).  Patch activity may continue through May but is suppressed by high summer temperatures.

The fungus does not kill stolons and roots within the patch. Therefore, new shoots will form in damaged areas with time. Zoysiagrass slowly recovers during the summer months.

Figure 3. Large patch symptoms in spring. Note damage is more severe at the lower mowing height.

Figure 4. Multiple patches on a zoysiagrass golf fairway in spring.

Figure 5. Large patch on buffalograss.

Conditions

The large patch fungus oversummers in the thatch as aggregated masses of fungal mycelium called bulbils. It does not produce spores, but can easily be moved from one location to another on contaminated sod.

The Rhizoctonia solani fungus that attacks zoysiagrass belongs to a different subgroup (AG 2-2 LP) and has lower temperature range (50 to 86 degrees F) for infection than the brown patch fungus that damages cool-season turfgrasses.  Therefore large patch almost always occurs during relatively cool weather in spring and fall whereas brown patch is a problem on cool-season in mid-summer. Large patch development is favored by frequent rains and excessive soil moisture.

Control

Large patch development is favored by high thatch and soil moisture. Avoid overwatering the turfgrass, especially in the fall or early spring. Poorly drained areas are very susceptible to injury from large patch and should be constructed (draining tiles, etc.) to avoid soil saturation. Avoid mowing the turfgrass in early morning when the thatch is spongy or wet. The fungus may be distributed in grass clippings during mowing.

Core aeration and/or vertislicing in June or July helps reduce thatch accumulation and invigorates the turfgrass. A reduction in the thatch layer should also help suppress large patch development. Do not core aerate or slice in early spring or at other times when patch symptoms are active! The fungus may be spread on infected turf cores removed during aeration. Early spring aeration may weaken the turf and slow the recovery process.

Early spring fertilization increases the possibility of a large patch epidemic. Begin fertilization only after large patch activity has stopped. This is usually sometime in mid- to late May. Research indicates that routine applications of slow-release forms of nitrogen in the summer (urea formaldehyde, turkey compost litter,) may slightly suppress severity of large patch in the fall. Avoid using more than 2 lbs/1000 sq. ft. of active nitrogen during the growing season. If large patch is severe in the spring, application of a fast-release form of nitrogen, such as urea, in late May or early June may help speed turfgrass recovery during the early summer months. Avoid using fast-release nitrogen forms in late summer. Several fungicides will help suppress large patch development, but the timing of application is critical to good disease control. Preventive applications should be applied in mid- to late September before large patch symptoms develop. As a general guideline applications should be made to areas with a previous history of the disease when thatch temperatures reach 70 to 75 degrees F.  Applications of azoxystrobin, flutolanil, PCNB, or triadimefon at the highest labeled rates have provided good control when used as a fall preventive treatment (see table). Fall preventive applications not only inhibit fall infection, but they also suppress or delay disease development in the spring. Fall and spring therapeutic fungicide applications are less effective in controlling large patch. Many of the zoysia shoots are severely damaged by the time the fungicide is applied. Because of the cool temperatures in spring and fall, the turfgrass cannot quickly recover from the injury. Nevertheless, curative fungicide treatments may prevent patches from further expanding during favorable weather.

excellent

preventive fall and spring

fair to good

poor preventive control but adequate curative

excellent

preventive fall and spring

fair to good

preventive, curative

fair to good

preventive

good to excellent

preventive fall and spring

good

preventive fall

excellent

preventive fall and spring

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Web updated 9/01/06
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