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Identification and Management of Turfgrass Diseases
Large patch
Symptoms and signs | Conditions | Management
Large patch is a cool-season disease of warm-season grasses. Symptoms are
most common when these grasses are either entering or coming out of dormancy.
Large patch is a sheath blight disease caused by a Rhizoctonia solani that is
in a different anastomosing group (AG 2-2 LP) than the R.
solani causing brown
patch in cool-season grasses.
Pathogen
Hosts
- Primarily zoysiagrass
- Buffalograss
- Bermudagrass
Symptoms and signs
Circular, slightly matted areas of straw-yellow zoysiagrass initially develop
in late September to early October during cool, rainy weather (Figure 1). During
favorable weather, the fungus progressively blights more shoots, resulting in
large, blighted patches of turfgrass with bright orange margins (Figure 2). Examination
of individual shoots within the patch reveals reddish brown to black lesions
at the base of the leaf sheaths, beyond which the leaf blades exhibit a yellow-orange
color (Figure 3). The yellow-orange color is due to an accumulation of anthocyanins
caused by girdling of the leaf sheath.
The yellow-orange margin is indicative of active disease, and the large,
cinnamon-brown colored hyphae of Rhizoctonia solani are most easily observed
in the leaf sheaths during this phase (Figure 4 top). Lesions normally do not
develop on the leaves. Depending on disease severity, unaffected, living shoots
may be scattered throughout the patch. Patches of blighted turf often exceed
20 feet in diameter.
Sheath infection can continue into November as 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 as well as buffalograss damaged by R.
solani reappear
in spring as light brown, sunken areas that are slower to recover from dormancy
than surrounding, healthy turfgrass (Figure 5). 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. New patches also may
develop in spring. The activity of R. solani usually continues through May but
is suppressed by high summer temperatures.
The fungus does not kill stolons and roots within the patch, and new shoots
will form in the damaged areas with time. Because infected zoysiagrass is slow
to recover, weed invasion in the thinned areas of the patch is common (Figure
6).
Conditions
Large patch symptoms can occur anytime during the growing season, but they
are most common in spring and fall as zoysiagrass enters or breaks winter dormancy.
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 (e.g., golf course
fairways) and where soil drainage is poor.
Large patch development is favored by heavy thatch. R.
solani oversummers
in the thatch as bulbils (resting structures). It does not produce spores, but
can easily be moved from one location to another on contaminated sod.
The R. solani that infects zoysiagrass belongs to a different subgroup (AG
2-2 LP) and has a 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 turfgrasses in midsummer.
Large patch development is favored by frequent rains and excessive soil moisture.
Management
Avoid overwatering the turfgrass, especially in the fall or early spring. Poorly
drained areas are especially susceptible to injury from large patch and should
be constructed (e.g., draining tiles) 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 cultivation or verti-slicing in June or July helps reduce thatch accumulation
and invigorates the turfgrass. A reduction in the thatch layer may also suppress
large patch development. Do not cultivate in early spring or at other times when
the disease is active. The fungus can be spread on infected turf cores removed
during cultivation, and physical damage associated with this cultural practice
can weaken the turfgrass 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 results indicate 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 pounds per 1,000 square feet of actual nitrogen during the growing
season. If large patch is severe in the spring, application of a quick-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 quick-release nitrogen forms
in late summer.
Several fungicides are effective at suppressing large patch development,
but the degree of success depends on timing of the application. Refer to Table
5 for a list of fungicides labeled for management of large patch. Preventive
applications should be made in mid- to late September before large patch symptoms
develop. As a general guideline, a single application should be made to areas
with a previous history of the disease when thatch temperatures reach 70 to 75
degrees F. A fall fungicide application not only inhibits fall infection, but
may also help suppress or delay spring symptoms. A spring (April) preventive
fungicide application may be necessary in locations with a history of severe
large patch.
Curative fungicide applications are less effective in controlling large patch.
Many zoysiagrass shoots are already damaged or killed by the time a curative
treatment is applied. Because of the cool temperatures in spring and fall, turfgrass
cannot quickly recover from the injury. Nevertheless, curative fungicide treatments
may prevent expansion of existing patches.
IPM1029, new June 2007
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