INOCULUM CONCENTRATION AND TIME OF APPLICATION OF GLIOCLADIUM-ROSEUM IN RELATION TO BIOCONTROL OF BOTRYTIS-CINEREA IN BLACK SPRUCE SEEDLINGS

Inoculum concentration and time of application of Gliocladium roseum B ainier were examined in relation to sporulation of Botrytis cinerea Pe rs.:Fr. in container-grown seedlings of black spruce (Picea mariana (M ill.) BSP) in greenhouses. Gliocladium roseum concentrations ranging f rom 10(2) to 10(8) conidia/mL water plus surfactant, applied four rime s at 2- to 4-week intervals starting when the seedling canopies closed , increasingly suppressed the proportion of seedlings with sporulation of B. cinerea (YI) during early and midphases of epidemics, and the p roportion of shoot length with sporulation of the pathogen (YS) throug hout the epidemics. Concentrations of 10(6) and 10(8) conidia/mL suppr essed YI and YS as or more effectively than did chlorothalonil (1.4 g active ingredient/L water) applied at the same times. One application of G. roseum (10(6) conidia/ml) when the seedling canopies were closin g suppressed YS as effectively as did programs of two to six applicati ons of the antagonist, or six of chlorothalonil, all at 1- and 2-week intervals beginning at canopy closure. The various programs generally did not affect YI. Logistic and Gompertz regression models were develo ped that adequately described YI and YS as functions of inoculum conce ntration and (or) time. It is concluded that G. roseum has potential a s a biological control agent against B. cinerea in production systems of black spruce seedlings.