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Disease Management

Cultural

Turfgrass cultural practices can be used to promote an environment where infection by S. homoeocarpa is limited. Monitoring fertility is an important first step to controlling dollar spot. Turfgrasses that are maintained under low nitrogen fertility are the most susceptible to infection from S. homoeocarpa, and they are slow to recover from dollar spot injury. Light and frequent nitrogen applications are recommended for disease management and maintenance of turfgrass growth. However, over-fertilization with nitrogen may cause an increase in the overall number of dollar spot infections, and also promote other diseases such as Pythium blight and Rhizoctonia brown patch.

Drought-stressed turf is particularly susceptible to S. homoeocarpa infection. Maintaining soil moisture near field capacity (-0.033 Mpa) will limit disease severity. When irrigation is required, enough water should be provided to achieve deep soil penetration. Irrigating in the late afternoon or evening should be avoided as this prolongs overnight periods of leaf wetness. Thatch layers should be removed if they are greater than 1.25 cm (0.5 inch) in depth. Thatch can be removed by vertical mowing and topdressing with sand or soil. Controlling thatch can improve drainage, reduce drought and nutrient stress, and remove sources of Sclerotinia inoculum. Compacted soil stresses the plants and slows turfgrass growth and recovery from disease, so routine cultivation is recommended. Excessively low mowing heights also stress turfgrass and favor dollar spot. Prune or remove trees and shrubs to promote good air movement and accelerated drying of the turfgrass canopy. Remove morning dew by either light irrigation or poling. This will help dissipate the guttation fluids which are nutrient-rich and provide S. homoeocarpa with a suitable growth medium.

Chemical

Fungicides in the following classes are effective for the control of dollar spot: benzimidazoles, demethylation inhibitors (DMI), dicarboximides, and nitriles. In addition, the carboximide boscalid, controls dollar spot (Figure 17). Fungicides should be applied when environmental conditions are favorable for disease development. Label rates of fungicides should be applied at either a 7-10 day or 14-21 day interval. Repeated use of some chemicals, particularly benzimidazoles and demethylation inhibitors has allowed resistant populations of S. homoeocarpa to develop. To limit the possibility of fungicide resistance, alternate the use of fungicides from different chemical classes (Figure 18).

Figure 17

Figure 18

Biological control

Extensive research has been conducted into the biological control of dollar spot. The disease has been suppressed in turfgrass research trials by applying either composted materials, the bacterium Enterobacter cloacae or the fungus Fusarium heterosporum. Research has also been conducted on the application of nonpathogenic strains of S. homoeocarpa. These strains interact with pathogenic strains and disease is reduced. BioJect Spot-Less (Pseudomonas aureofaciens) and EcoGuard (Bacillus licheniformis SB3086) are two biological control products that are currently registered for dollar spot control. Research has also been conducted with some success using several composted materials including turkey litter, sewage sludge, and uncomposted blends of plant and animal meals. Disease suppression has been achieved with these products in turf exhibiting light to moderate dollar spot infestations.

Resistant species and cultivars

There are some resistant species and cultivars of commonly used turfgrasses available (Figure 19). Among the cool-season grasses, perennial ryegrass (Lolium perenne) and tall fescue (Festuca arundinacea) are less susceptible to S. homoeocarpa than other commonly used species. Colonial bentgrass (Agrostis tenuis) is less susceptible than creeping bentgrass (Agrostis palustris). Annual bluegrass (Poa annua) is more susceptible than bentgrasses. Cultivars of creeping bentgrass vary in their susceptibility to S. homoeocarpa, but none is highly resistant. Among the warm-season grasses, dollar spot is particularly severe on bermudagrass (Cynodon dactylon) and seashore paspalum (Paspalum vaginatum). Consult local turfgrass extension personnel for information on resistant species and cultivars when establishing a new turfgrass area. In addition, information on the level of susceptibility of specific turfgrass species and cultivars can be obtained from the National Turfgrass Evaluation Program (www.ntep.org).

Figure 19