Factors Promoting Infestation of Newly Planted, Nonbearing Apple Orchards by Dogwood Borer (Lepidoptera: Sesiidae)

Abstract

The initiation and level of infestation by dogwood borer, Synanthedon scitula (Harris), was tracked over three consecutive years in two nonbearing apple (Malus spp.) orchards in West Virginia and Virginia. The orchards were planted on a number of rootstock-variety (approximately cultivar) combinations and grown using different cultural practices. Infestations were detected during the first season after planting and continued to increase annually. The amount of burr knot tissue had the greatest impact on dogwood borer populations, because increasing amounts of burr knot tissue resulted in higher infestation rates. The use of plastic spiral wrap tree guards seemed to increase the development of burr knot tissue, resulting in significantly greater infestation compared with trees without tree guards in the West Virginia orchard. Variety also had a significant effect, because 'Idared' trees on M.26 had significantly greater levels of infestation compared with 'Buckeye Gala' on M.26, with or without tree guards, in the Virginia orchard. Mounding soil around the rootstock to a height just above the graft union prevented or tremendously curtailed infestation by dogwood borer, but it led to scion rooting that seemed to have an impact on size-controlling features of dwarfing rootstocks. Removal of the mounds at the beginning of the third growing season resulted in infestation of the rooted tissue during the same season. As long as apple cultivars continue to be planted on size-controlling rootstocks, dogwood borer will likely remain a serious pest, requiring either chemical treatments or a behavioral control strategy, such as mating disruption, to protect trees from infestation and damage.