Control of peach scab with reduced midseason fungicide programs

The effectiveness of reduced fungicide programs, using either extended application intervals or alternate-row middle (ARM) spraying of wettable sulfur or captan, on infection of peach fruit by Cladosporium carpophilum was investigated in a 2-year study in Georgia. Fungicide reductions focused on the midseason cover spray period when scab pressure is typically reduced and when growers would be most likely to adopt reduced spray programs because of the potential for fewer insecticide applications at the same time. In an experimental orchard, sulfur was applied at calyx split and calyx fall, followed by another application of sulfur or captan at first cover. Subsequent midseason applications consisted of sulfur at 12- to 14-day intervals (standard); sulfur at extended 24- to 28-day intervals; or either sulfur or captan applied via ARM spraying at 12- to 14-day intervals at reduced sprayer speed. Plots without midseason sprays after first cover also were included. Fruit scab severity was reduced by all fungicide programs compared with the untreated control. Disease severity with sulfur applied at extended intervals and with ARM spraying of sulfur or captan was not significantly different from that of the standard (P > 0.05) in both years, suggesting that application intensity during midseason can be reduced without compromising scab control. By contrast, plots that did not receive any midseason sprays after first cover had significantly more disease. Reduced midseason applications of sulfur were further evaluated in two commercial orchards. In one orchard, fruit scab control achieved with extended-interval or ARM spraying during midseason was not significantly different from that of the grower standard. In the second orchard, higher disease severity resulted from midseason ARM applications compared with the standard, presumably because of the longer (14- to 18-day) spray interval used by the cooperating grower for ARM spraying. Reduced midseason fungicide programs did not lead to an increased carryover of inoculum as determined by conidial counts on overwintered twigs at petal fall in the following year.