IPM Identification and Mangement Of Turfgrass Diseases

Author(s)

Leaf and Sheath Spot

Pathogen: Rhizoctonia zeae
Hosts: Primarily Kentucky bluegrass, annual bluegrass and creeping bentgrass, but also perennial ryegrass and tall fescue

Symptoms and signs

In Missouri, leaf and sheath spot was first observed on a mixed Kentucky bluegrass/perennial ryegrass athletic field in 2000. Symptoms occurred only on the Kentucky bluegrass in this mixed stand. Since then the disease has been identified on other Kentucky bluegrass athletic fields and sod fields, on perennial ryegrass from a tee and in association with tall fescue. Symptoms in these situations occurred from early to late August under high temperatures.

The symptom on Kentucky bluegrass usually appears as sporadic, dinner-plate-sized rings of yellowed grass (Figure 1). The grass to the inside of the patch is usually darker green in color. Sometimes the disease appears to be more of a general blight (Figure 2). Sheath blight symptoms are commonly visible on individual plants at the margin of a patch (Figure 3).
The hyphae (individual fungal strands) of Rhizoctonia zeae have the characteristic right-angled branching pattern typical of other Rhizoctonia species. Additionally, numerous bulbils have been observed in association with this disease on Kentucky bluegrass, perennial ryegrass and tall fescue. The pink to orange bulbils are about the size of BBs and range in shape from round to irregular. Bulbils have been observed on the surface of decaying grass tissue and embedded in leaf tissue (Figures 4 and 5).
R. zeae has also been reported to cause yellow ring symptoms on creeping bentgrass and annual bluegrass on putting greens. On mixed greens, the disease usually occurs on one or the other species and not both. Bright yellow rings reaching several feet in diameter form in May and June under moderate temperatures (Figure 6). Leaves and leaf sheaths may not exhibit extensive symptoms, but fungal mycelium characteristic of Rhizoctonia spp. is usually present on tissue. Bulbils have rarely been observed in association with the yellow ring symptom on bentgrass or annual bluegrass in contrast to the disease on Kentucky bluegrass, perennial ryegrass and tall fescue. Symptoms on putting greens may resemble those of fairy ring or yellow patch. Laboratory examination may be necessary for confirmation.

Conditions

Little is known about the conditions favoring disease development on Kentucky bluegrass, except that in Missouri it has been observed under high temperatures in August. In contrast, ring symptoms on putting greens tend to occur in late spring or fall during relatively mild temperatures.

As with other diseases caused by Rhizoctonia spp., high relative humidity, abundant soil moisture, and heavy rainfall or irrigation tend to make leaf and sheath spot more severe.

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.