Michael A. Fidanza

Environmental Monitoring and Exploratory Development of a Predictive Model for Dead Spot of Creeping Bentgrass

Dead spot of creeping bentgrass is incited by Ophiosphaerella agrostis. The objectives of this 3-year field study were to: (i) elucidate environmental conditions associated with the expression of dead spot symptoms, (ii) develop a model to assist in predicting the appearance of dead spot symptoms and epidemics in creeping bentgrass, and (iii) elucidate the association between ascospore release and the appearance of new dead spot symptoms. Environmental parameters measured included relative humidity (RH), air (AT) and soil (ST) temperatures, solar irradiance (SOL), precipitation and irrigation (RAIN), and leaf wetness duration (LWD). Dead spot symptoms generally did not occur at temperatures (air or soil) below 15°C. Two descriptive models were developed that predicted the appearance of dead spot symptoms with an accuracy of 74 to 80%. Between 1 May and 31 October 2000 to 2002, the appearance of new dead spot infection centers was most accurately predicted (80%) by the single parameter of STMean ≥ 20°C. In years with severe levels of dead spot, the occurrence of major infection events was predicted on 37 of 40 days (93%). A combination of elevated air (ATMax ≥ 27°C) and soil (STMean ≥ 18°C) temperatures, low relative humidity (RHMean ≤ 80%), shortened periods of leaf wetness (LWD ≤ 14 h), and high levels of solar radiation (SOLMean ≥ 230 W m-2) were associated with the development of major dead spot epidemics. Ascospore discharge and the appearance of new infection centers occurred in a cyclic pattern that peaked about every 12 days. New infection centers appeared 3 to 10 days after the release of a large number of ascospores.

Characterization of soil properties associated with type-I fairy ring symptoms in turfgrass

Fairy ring is a frequently reported disease of turfgrasses worldwide, and necrotic or severely injured grass are observed in those turf sites exhibiting type-I fairy ring symptoms. The objective of this research was to characterize soil chemical and physical properties at two soil sampling depths (0.5 cm and 3.0 cm) at a turfgrass site exhibiting type-I fairy ring symptoms. Soil samples were obtained from a perennial ryegrass (Lolium perenne L.) golf course fairway at one sampling date in the summer when environmental conditions were most conducive to the appearance of severe type-I fairy ring symptoms. At both soil depths, soil analysis indicated that concentrations of ammonium-nitrogen, potassium, and sulfur were statistically higher in soil underlying necrotic or bare zones versus soil in healthy turfgrass zones. At both soil depths, soil electrical conductivity was statistically higher, and volumetric soil water content was statistically lower in necrotic zones versus soil under healthy turfgrass. At both soil depths, total nitrogen, magnesium, calcium, cation exchange capacity, and organic matter content were not statistically different among necrotic and healthy turfgrass zones. Soil pH was statistically higher in the necrotic zone versus soil under healthy turfgrass at only the 3.0 cm soil sampling depth. Comparing soil properties within the necrotic zone, only potassium and electrical conductivity was statistically higher at the 0.5 cm depth compared to the 3.0 cm depth. Although most soil information was considered very similar at both sampling depths, soil sampling at the 3.0 cm depth would be a more practical or easier method for turfgrass managers. At either soil sampling depth, the necrotic zones of type-I fairy ring areas in turfgrass were most likely associated with a combination of direct and indirect effects of the basidiomycete fungi on soil chemical and physical properties in the turfgrass root zone.