IPM Identification and Mangement Of Turfgrass Diseases

Author(s)

Yellow Tuft
(downy mildew)

Pathogen: Sclerophthora macrospora
Hosts: creeping bentgrass, Kentucky bluegrass, annual bluegrass, zoysiagrass, others less common

Symptoms and signs

On bentgrass or annual bluegrass putting surfaces, yellow tuft occurs as bright yellow spots ranging in diameter from ½ to 1 inch (Figure 1). The spots are individual plants infected with Sclerophthora macrospora, which results in the production of many more tillers than normal (Figure 2). The excess tillering is a condition commonly known as tufting. Tufted plants are shallowly rooted and easily removed from the turf surface. In some regions, infected plants are prone to winterkill, probably as a result of heaving due to the shallow roots (Figure 3).

Yellow spots in Kentucky bluegrass or zoysiagrass are larger than those seen on putting surfaces, depending on turfgrass density and height of cut (Figure 4). Where normal creeping bentgrass and Kentucky bluegrass commonly have fewer than eight tillers, infected plants have 15 or more (Figure 5). In infected zoysiagrass, the excess tillering is often associated with individual nodes rather than individual plants. Infected zoysiagrass can have 30 or more tillers per node in contrast to the normalthree to four (Figure 6).
Under cool moist conditions in spring and fall, S. macrospora produces sporangia (fruiting bodies) on turfgrass leaves. Sporangia are best seen early in the morning under heavy dew. They are pearly white and give a downy appearance to leaf surfaces when viewed with a hand lens. The sporangia are ephemeral, quickly collapsing when the leaf surface dries. In the field it is more common to see the collapsed sporangia as a gray to white crystalline residue on the leaf surface (Figure 7). When turgid, the sporangia are lemon shaped (Figure 7 inset) and contain zoospores (motile spores). Zoospores swim in free moisture to infect adjacent healthy meristematic tissue in just a few hours. Oopores (sexualspores) are sometimes produced in infected leaf tissue but are more numerous and easier to detect in crabgrass species.
In zoysiagrass sod fields and on zoysiagrass surrounds, infected stands are often thin and yellow as the grass breaks dormancy in the spring (Figures 8, 9 and 10). Infected zoysiagrass is stunted and extensively tufted (Figure 10 inset). On zoysiagrass fairways, the disease often appears as a more diffuse yellowing without extensive tufting (Figure 11). Yellow tuft of zoysiagrass is more severe on shaded areas of fairways.

Conditions

Yellow tuft is favored by cool (41 to 68°F), wet conditions. Severe symptoms can occur in low-lying, poorly drained areas of sod production fields or fairways. In turf prone to periodic flooding, especially in the spring or fall, S. macrospora infection is likely.

Crabgrass is very susceptible to yellow tuft, and large numbers of oospores, which serve as a source of inoculum, are produced in infected tissues. Sod production fields with heavy crabgrass pressure can have a greater incidence of yellow tuft.

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.