IPM Identification and Mangement Of Turfgrass Diseases

Author(s)

Dead Spot

Pathogen: Ophiosphaerella agrostis
Hosts: Primarily bentgrass, hybrid bermudagrass

Symptoms and signs

The first symptoms of dead spot on bentgrass appear as reddish brown patches about ½ inch in diameter (Figure 1). The patches are most common on mounds, ridges, slopes and other historically dry areas on the putting surface. The diameter of the patches never gets much larger than 3 inches, and the patches do not coalesce. The patches are often sunken, interfering with putting quality. In the early stages of disease development, the small patches may be mistaken for ball marks or copper spot. As the disease progresses, the inner area of the patch turns light tan and at this stage can resemble dollar spot (Figure 2). When the fungus is active, the outer margins of the patch are red-brown to orange.

Disease generally starts in May, continuing throughout the summer until the first hard frost. Disease incidence varies among locations of greens, and the number of infection sites per green can range from a few to several hundred. New growth into the patch is inhibited, so recovery is slow.
All plant parts become infected, including leaves, leaf sheaths, roots and stolons. Unlike the dollar spot fungus, Ophiosphaerella agrostis generally does not produce visible mycelium (mass of fungal vegetative growth) in the field. One can sometimes observe a pink to white mycelium when plugs with symptoms are incubated in a moist chamber for several days.
Pseudothecia (fruiting bodies) develop in abundance in leaves, leaf sheaths and stolons (Figure 3). The pseudothecia are darkly pigmented, flask-shaped structures detectable with a hand lens (Figure 4). Ascopores are produced in pseudothecia in saclike structures (asci) (Figure 5). Mature ascospores are forcibly discharged or exude from the fruiting bodies under conditions of high relative humidity. Ascospores are easily spread by rainfall and irrigation water to initiate new infection sites.

Conditions

Dead spot most commonly occurs on new greens or greens treated with methyl bromide during a renovation project. The disease has not been observed on fairways with underlying native soil. The disease gradually disappears, presumably in response to the buildup of competitive microorganisms in the new or fumigated root zone.

Dead spot is a high-temperature (77 to 86°F), low-moisture disease in which symptoms most commonly occur on areas of the green most prone to drying.

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.