IPM Identification and Mangement Of Turfgrass Diseases
Yellow Patch
Pathogen: Rhizoctonia cerealis
Hosts: primarily creeping bentgrass, also annual bluegrass, Kentucky bluegrass
or arc-like patterns ranging in size from a few inches to several feet develop in affected turf. In many cases, only a 1- to 3-inch-wide band of discolored turf is present and the turfgrass inside the ring may show no adverse effects (Figures 1 and 2).
In other cases, turf inside the ring is dis-colored a light yellow, lending a more patch-like quality to the symptoms on the putting surface (Figure 3). Early stages of yellow patch are most noticeable early in the morning, then difficult to see by midday. Infected plants exhibit a light, water-soaked lesion at the base of the leaf sheaf or in the crown tissue (Figure 4). Lesions on the leaf blade are rare.
A cobwebby growth of mycelium may be visible early in the day when dew is present, but it is sparser than that seen with brown patch. It is usually necessary to use a stereo microscope to detect the mycelium (Figure 5). The hyphae exhibit right-angled branching characteristic of other Rhizoctonia species (Figure 6). Rhizoctonia cerealis is somewhat similar to, but distinct from, Rhizoctonia species that cause leaf and sheath spot, large patch of zoysiagrass and brown patch of cool-season turfgrasses. R. cerealis is binucleate (two nuclei per cell), in contrast to R. zeae and R. solani, which are multinucleate.
The fungus survives in the soil as bulbils (resting structures). Bulbils are initially light colored, then dark brown when mature. The pinhead-sized bulbils can be numerous in the thatch surrounding damaged turfgrass.
The rings are most conspicuous in the early spring, because they contrast sharply with newly emerging leaves. In most cases the symptoms remain superficial, with rings that are difficult to see. Infected plants recover quickly when temperatures increase. During prolonged cool, wet periods in late winter to early spring, patches can become necrotic and sunken. These damaged areas do not recover quickly.
Yellow patch development is favored by extended periods of wet, cloudy weather. It is a cool-temperature disease (50 to 65°F). Disease development is greatly suppressed at temperatures lower than 45°F and greater than 75°. Yellow patch tends to be more severe on putting greens with poor subsurface drainage.
The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality.
