IPM Identification and Mangement Of Turfgrass Diseases
Drechslera Leaf Spots
Pathogen: Drechslera spp.
Hosts: D. poae - Kentucky bluegrass, annual
bluegrass, tall fescue and fine-leafed fescues; D.
erythrospila – creeping bentgrass, colonial bentgrass
This disease was once considered the most important spring and fall disease of Kentucky bluegrass, but the widespread use of resistant bluegrass cultivars has lessened the impact of this disease. Still, some leaf spot can be found on most home lawns in the spring, and it can damage newly seeded lawns and certain susceptible cultivars of Kentucky bluegrass. This disease can sometimes be severe on tall fescue.
Drechslera leaf spot and melting-out develops in late March through mid to late May, reoccurring in the fall. Infected plants initially develop small elliptical purple leaf spots (Figure 1). The spots turn light gray or tan but remain bordered by a dark brown to purple margin (Figure 2). Leaf tissue surrounding the spots may turn yellow. The leaf spot phase of the disease usually does not damage the plant significantly. However, the fungus can also infect the crown, rhizomes and roots. As daytime temperatures increase, leaves on crown-infected plants turn light green or yellow, similar to nitrogen-deficient turf. Eventually these plants die and turn brown or straw colored. This is referred to as the melting-out phase of the disease. Severe melting-out results in irregular patches of dead turf. Damaged lawns are thinned and subject to weed invasion. Symptoms on tall fescue are similar to those on bluegrass.
Drechslera poae, as well as other fungi in this general group, sporulates to produce multicelled, darkly pigmented conidia (spores). As illustrated with a similar fungus, Bipolaris sorokiniana, sporulation occurs on the surface of infected grass tissue (Figure 3). The conidia are easily spread by wind, water and mowing, and the dark pigmentation makes them resistant to breakdown by ultraviolet light.
Red leaf spot
Red leaf spot is more common on colonial bentgrass than on creeping bentgrass. In the last several years, however, the disease has occurred with increasing frequency on several newer creeping bentgrass cultivars.
Red leaf spot is a high-temperature disease, occurring in June through August. The first noticeable symptoms on the putting surface are small brown to red patches, ranging in size from 1 to 8 inches or more (Figure 4). Under favorable conditions for disease development, the infection centers can coalesce to blight large areas of the putting surface (Figure 5). Unlike other leaf spot diseases on the larger-bladed turfgrasses, a true leaf spot symptom is difficult to see on creeping bentgrass. By the time the red patches are observed on the putting surface, individual leaf blades have usually shriveled (Figure 6). Conidia (spores) can often be observed with the aid of a hand lens (Figure 7). Morphologically the conidia are similar to those produced by other genera of fungi in this group (Figure 7, inset).
Leaf spot fungi overwinter in the thatch layer or in small lesions on leaf blades. Drechslera leaf spot and melting-out is favoredby long periods of leaf wetness and moderate temperatures. D. poae is inhibited by hot weather and rarely appears during the summeror early fall.
Red leaf spot
Red leaf spot is favored by hot, dry conditions. Some bentgrass cultivars appear to be more susceptible than others.
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.
