Evaluation of Metalaxyl and Captafol Soil Drenches, Composted Hardwood Bark Soil Amendments, and Graft Union Placement on Control of Apple Collar Rot

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Abstract
Protectant applications (soil drenches) of metalaxyl and captafol provided control of apple collar rot on trees inoculated with Phytophthora cactorum in the field. Eighty-one percent of all inoculated, untreated trees developed typical collar rot symptoms and died before the end of the study. No inoculated trees treated with metalaxyl and only one treated with captafol developed collar rot. Incorporation of a 1:1 mixture of composted hardwood bark and field soil into the planting hole at time of planting resulted in significantly fewer infected trees than untreated controls but significantly more infected trees than either fungicide treatment. Placement of the graft union on susceptible rootstock above or below the soil line appeared to have no effect on collar rot control.