SEASONAL BIOLOGY AND CONTROL OF THE DOGWOOD BORER, SYNANTHEDON SCITULA (LEPIDOPTERA: SESIIDAE) ON CLONAL APPLE ROOTSTOCKS IN NEW YORK

The dogwood borer, Synanthedon scitula (Harris), is a relatively new pest problem on apples. Larvae feed principally in burr knots on the above-ground portion of clonal rootstocks. According to a survey of 33 orchards on dwarf or semidwarf apple root-stocks, about 70% of the trees had burr knots. The tendency to develop burr knots was similar among the rootstocks examined in this survey. The proportion of trees infested with dogwood borer in an orchard ranged from 0 to 100% and averaged 30%. The dogwood borer overwinters in the larval stage (2nd to 6th instar) and pupates in the feeding tunnel. Emergence and pheromone-trap records indicate 1 generation a year. In western New York, adults begin to emerge in mid-June, peak in mid-July, and continue to emerge through September. In several tests conducted over a 3-year period, chlorpyrifos at 180 g/100 L provided the most consistent control. At this rate a single spray timed to first or peak egg hatch was as effective as 2 sprays. Latex paint applied by brush to the trunk at the beginning of the oviposition period also reduced the infestation. In established plantings, dogwood borer can also be controlled by berming with soil up to the graft union to prevent access to burr knots. Destroying burr knots chemically with naphthalene acetic acid will not eliminate an infestation and may invite other borer problem