Yellow Patch of Creeping Bentgrass

Ned Tisserat
Extension Specialist, Plant Pathology

Symptoms

Yellow patch, also called cool-season brown patch, is primarily a problem on bentgrass putting greens from November through April. The disease often results in superficial ring patterns in the turf that quickly recover during warm weather. However, yellow patch can cause significant turf discoloration during periods favorable for infection.

Figure 1. Yellow patch on a bentgrass green.

Yellow patch symptoms may initially appear in late October or early November during relatively cool (40 to 60 F), wet weather. Yellow to rusty-red rings 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. Turf inside the ring may show no adverse effects, resulting in a frogeye appearance. In other instances, turf inside the ring is discolored a light yellow. This gives the disease a more patch-like quality. Early stages of yellow patch are most noticeable early in the morning. Symptoms may be difficult to see by midday. Affected plants exhibit a light, water-soaked lesion at the base of the leaf sheaf or on the crown tissue. Leaf lesions are rarely visible. A cobwebby growth of mycelium may be visible early in the day if dew is present.

Symptoms of yellow patch tend to subside in December and then reappear in late February and March. The rings are the most conspicuous at this time because they contrast more sharply with the newly emerging bentgrass leaves. In some cases the damage may remain somewhat superficial. Affected plants remain yellow but recover quickly when temperatures increase. However, rings can become necrotic and sunken during prolonged cool, wet weather. These damaged areas do not recover quickly.

Conditions

Yellow patch is caused by a fungal pathogen called Rhizoctonia cerealis. This fungus is somewhat similar to, but distinct from, the Rhizoctonia fungi responsible for large patch disease of zoysiagrass and brown patch of cool-season turfgrasses. The fungus survives in the soil as a hard resting structure called a bulbil. The structures, about the size of a pinhead and dark brown, may be numerous in thatch surrounding damaged turfgrass.

Disease Management

Yellow patch tends to be more severe on putting greens with poor subsurface drainage. Core aerification in fall may help reduce disease severity. Although there is no direct evidence that high nitrogen rates increase disease severity, avoid excessive nitrogen fertilization in fall. Other cultural practices appear to have little influence on disease development.

Yellow patch can be suppressed by preventive fungicide applications. Make the first application before or as soon as symptoms begin to develop in late October or early November. In most years, a single application is sufficient to suppress yellow patch throughout the entire winter and spring. During wet, mild winters with high disease activity, make a second fungicide application in late March. Several fungicides (see table ) are effective when used as preventive treatments. Unfortunately, these fungicides are much less effective when applied as curative treatment.

azoxystrobin

excellent

preventive in fall (Nov.)

Heritage

flutolanil

excellent

preventive in fall (Nov.)

Prostar

iprodione

good

preventive in fall, curative?

Chipco26019, Proturf, Fungicide X

myclobutanil

good

preventive in fall (Nov.)

Eagle

propiconazole

good

preventive in fall (Nov.)

Banner

trifloxystrobin

good

preventive in fall (Nov.)

Compass

triadimefon

excellent

preventive in fall (Nov.)

Bayleton, Accost, Granular Turf Fungicide, Proturf Fungicide VII, others

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