IPM Identification and Mangement Of Turfgrass Diseases

Author(s)

Copper Spot

Pathogen: Gloeocercospora sorghi
Hosts: Bentgrass, bermudagrass, zoysiagrass

Symptoms and signs

Although Gloeocercospora sorghi initially causes a leaf spot on creeping bentgrass, this phase of the disease is rarely observed in the field, because infected leaves are rapidly blighted. Usually the first indication of disease is the appearance of pinkish orange to copper-colored patches with irregular margins (Figure 1). The patches range from 1 to 3 inches in diameter, but under favorable conditions for disease development, patches often coalesce. Symptoms can also occur in streaks, because the fungus is easily spread by water and equipment.

The color of the patches is more pronounced under moist conditions that favor production of sporodochia (fruiting bodies). The conidia (spores) are produced on the sporodochia in gelatinous masses that can be observed with a hand lens. Look for pink to salmon-colored gelatinous spore masses protruding from leaf surfaces (Figure 2). The long, needle-like conidia within a spore mass are multicelled and usually curved (Figure 3).
Symptoms are easily confused with those of anthracnose basal rot, brown patch, dollar spot, Pythium blight or red leaf spot. Dollar spot occurs under slightly cooler temperatures and the infection sites tend to be tan rather than pink. Temperatures favorable for optimum development of Pythium foliar blight and red leaf spot coincide with those of copper spot. Red leaf spot patches on a putting green are less defined than those of copper spot. Initial infection sites of Pythium foliar blight also have a similar color to those of copper spot, but Pythium foliar blight develops under higher temperatures and is rare on greens-height bentgrass. Copper spot infection sites are generally more discrete than those of anthracnose basal rot, which are more diffuse.

Conditions

The disease is reported to be more common and severe on velvet bentgrass than on creeping bentgrass. It is also more severe under acidic soil contions. This may account for the sporadic nature of the disease, because the soil pH of many putting greens is high.

G. sorghi produces huge quantities of conidia in warm, moist weather (68 to 86°F). Disease severity increases with prolonged periods of leaf wetness. Under these favorable conditions, the pathogen is readily spread if the turfgrass is mowed when the leaves are wet. The pathogen is also easily spread by splashing water (rainfall or irrigation) and through surface runoff. Spread also occurs in relation to the activities of people and animals. Excess available nitrogen enhances disease development.

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.