Controlling Gray Mold on Container-Grown Douglas-Fir by Modified Styroblocks and Under-Bench, Forced Air Ventilation

Abstract

Abstract Gray mold (Botrytis cinerea) control on Douglas-fir (Pseudotsuga menziesii) seedlings was investigated using under-bench ventilation and styroblocks (growing containers) modified with vertical ventilation holes to allow air movement through the seedling canopy. Gray mold incidence and severity were reduced in three treatments: modified styroblocks with aeration holes at each intercavity intersection and vented from below with heated forced air, like the preceding treatment, but vented with unheated forced air, and modified styroblocks vented with unheated unforced air. In vented styroblocks, gray mold occurred on 25% of the 7-month-old seedlings compared to greater than 75% incidence in unmodified (control) styroblocks. Disease on individual seedlings was also less severe in ventilated styroblocks. The reduced incidence of gray mold in the treatments with ventilation was attributed to more rapid drying of seedling foliage following irrigation. The lowest incidence of humidity and temperature episodes that were ideal for gray mold spore germination and infection occurred in the canopy of seedlings grown in the unheated forced air ventilation treatment There were no practical differences in seedling heights or root collar diameters among treatments. Use of ventilated styroblocks should significantly reduce both gray mold losses and fungicide usage in nurseries. West. J. Appl. For. 5(3):75-79, July 1990