Effect of Temperature and Postharvest Field Burning of Kentucky Bluegrass on Germination of Sclerotia ofClaviceps purpurea

Sclerotia of Claviceps purpurea were collected from Kentucky bluegrass (Poa pratensis) seed fields and exposed to various temperature regimes in a kiln. Sclerotia lost their ability to germinate when exposed to 200°C for 116 s, 300°C for 48 s, or 400°C for 15 s. Exposures of 240 s at 100 and 50°C produced only a slight reduction in germination compared to controls. The effect of temperatures produced by open-field and machine burning of residues also was determined. Peak soil-surface temperatures produced by open-field burning of Kentucky bluegrass postharvest residue were 120°C in 1990 and 240°C in 1991 at Rockford, WA. An experimental machine burner produced soil-surface temperatures of 280°C in 1990 and 320°C in 1991. Temperatures at 1 and 3 cm below the soil surface did not significantly change with any field treatment. Machine and open-field burning, compared to the nonburn control, significantly lowered (1990) or eliminated (1991) germination of sclerotia on the soil surface. None of the treatments significantly altered germination of sclerotia buried at 1 and 3 cm. These results indicate that the higher the temperature from burning residue, the greater the reduction in sclerotial viability.