A forecasting model for fire blight of pear.
Bactericide applications for Erwinia amylovora control were forecast by using daily mean orchard temps. Bacteria were detected in flowers in 11 of 12 orchards in 1977 within 2 wk after the mean temp. exceeded a prediction line drawn from 16.7 deg C on 1 Mar. to 14.4 deg on 1 May. During 1974, 1975 and 1976 the bacteria were detected in 93% of orchards 22 days or more after the crossing of the prediction line. These epiphytic bacteria were isolated from healthy pear flowers before any fire blight appeared in the orchard in 100% of the orchards monitored during 1974-77. Treatments initiated soon after the mean temp. exceeded the prediction line gave control equal to a spray programme initiated at 10% bloom and which entailed more applications. Reduction in the number of orchard applications depended on spring temps. In 1974 and 1975, the number was reduced by >60% but in 1977 reduction averaged only 1 application. In 1978 the estimates in Calif. indicated a saving of 32 applications/grower on c. 16 2000 ha for a total saving of $1.2 million. Modifications of this technique may be applicable to other pear growing areas.