IPM Identification and Mangement Of Turfgrass Diseases

Author(s)

Dollar Spot

Pathogen: Sclerotinia homoeocarpa
Hosts: creeping bentgrass, Kentucky bluegrass, perennial ryegrass, zoysiagrass, bermudagrass, buffalograss

Symptoms and signs

In higher cut turfgrass, Sclerotinia homoeocarpa infection results in the formation of small, roughly circular tan patches. Patch size varies with mowing height and environmental conditions and can range from a few inches to 6 inches or more in diameter (Figure 1). During extended periods of disease-favorable weather, patches coalesce into large, irregular, dead areas. Infected plants within the diseased spots wilt and eventually turn tan or brown because of girdling lesions on the leaf blades. This can result in substantial damage to the turfgrass.

On putting greens, dollar spot infection sites rarely exceed 2 inches in diameter (Figure 2). During weather that is favorable to dollar spot, hundreds of spots can coalesce to blight large areas of the putting surface. If left untreated, the spots become sunken, leaving a low-quality, pockmarked putting surface.
Foliar symptoms of dollar spot can be seen on plants at the transition zone between healthy and infected turfgrass. On Kentucky bluegrass, the lesions appear as bleached areas with a constricted or hourglass appearance, usually with reddish brown borders (Figure 3). The lesions are often located near the middle of the leaf and extend completely across the leaf blade. On creeping bentgrass, individual infected leaves exhibit light tan lesions that may or may not be surrounded by a dark, reddish-brown border (Figure 4). The lesions are difficult to see on closely mowed bentgrass without a hand lens. On warm-season grasses (bermudagrass, buffalograss and zoysiagrass) the symptoms occur as discrete lesions bordered by brown bands (Figure 5).
In the early morning when dew is still present on the turfgrass, small cottony webs of fungal mycelium can sometimes be seen growing from the diseased leaf blades (Figure 6). This growth can be confused with spider webs, “cotton” from plant seeds, or other fungi, and therefore is not a reliable diagnostic feature.
When viewed under a compound microscope, the fungal hyphae have a characteristic Y-shaped branching, in contrast to hyphae of Rhizoctonia solani, which are predominantly right-angled (Figure 6 inset).

Conditions

Dollar spot is more prevalent in nitrogen-deficient turfgrass. S. homoeocarpa survives indefinitely in thatch and soil. In the presence of a thin film of moisture on leaves and moderate temperatures (65 to 85°F), the fungus infects leaves. S. homoeocarpa rarely infects turfgrass roots, although fungal toxins may adversely affect root formation. Dollar spot is most severe in late spring and early summer and again in early fall; however, it can occur throughout the summer months. The patches are more numerous in areas where air circulation or soil drainage is poor.

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.