Action thresholds for managing apple scab with fungicides and sanitation

摘要

Two action thresholds are presented: a "reduce,fungicide" action threshold and a "sanitation" action threshold. They were developed to replace a "PAD" action threshold and related "sanitation" action threshold that had been reported previously, because the procedure to calculate PAD (potential ascospore dose) was too detailed to be readily adopted by growers. Both action thresholds are based on the number of scabbed leaves counted on 600 extension shoots examined in autumn. If 50 scabbed leaves are counted, the orchard is considered to be "low-risk," and several tactics may be used that will reduce the recommended fungicide dose. If 50-100 scabbed leaves are counted, the orchard is considered to be "moderate-risk," and the recommendation is to employ sanitation, i.e., shred the leaf litter or treat the leaf litter with urea, and then select tactics for controlling scab listed for a "low-risk" orchard.