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Larry J. Gut, Peter H. McGhee and Ron Perry

The relationship between the extent of burrknots on apple rootstocks and dogwood borer (DWB) [Synanthedon scitula Harris] infestation, and the efficacy of a cultural management strategy for this pest were studied in heavily infested plots at the Michigan State University Clarksville Horticulture Experiment Station. Spearman rank correlation Rho values of 0.85 and 0.75 in consecutive years of the study substantiated a strong positive correlation between the number of larvae present in the rootstock and the surface area of the rootstock covered by burrknots. Cultivar type affected the level of the DWB infestation in the rootstock. Larval densities were 8- to 10-times higher in Mark rootstocks when the grafted scion was `Idared' instead of `Liberty'. This cultivar related difference in larval infestation was associated with a greater number of burrknots on `Idared'/Mark compared to `Liberty'/Mark trees. Mounding of soil to cover the exposed rootstock was found to be a highly effective alternative to insecticides for DWB control. Under conditions of heavy pest pressure, this cultural control tactic provided 76% to 99% reductions in larval densities. These levels of control are comparable to or better than those reported for trunk sprays with chlorpyrifos, the most effective of currently available insecticides.