Carpenterworm Management in Walnuts

Research into practical control methods for carpenterworm, Prionoxystus robiniae (Peck), a large wood boring larva, was continued. Observations indicate this pest primarily attacks older trees of the Hartley variety that are infected with deep bark canker, a stress-related bacterial disorder. Carpenterworm (CW) also attacks the Franquette variety. Hartley orchards with substantial deep bark canker appear capable of sustaining moderate production until the addi tioncU stress factor of CW is encountered; this results in a much more rapid decline in orchard quality and yield. ResuLts from monitoring adult flight activity correlated with observations made in figs: CW adults begin emerging during the second or third week of March and end by the first week in July. The initial date and rate of emergence is quite temperature dependent. Fall application of two parasitic nematode species, Neoaplectana carpocapsae and N. bibionus, indicated that neither could be applied by a backpack blower-mister (simulating a speedspray application) and obtain successful CW zontrol even with concentrations of approximatley 3000 nematodes/cm. Fall applications using a commercially available hand-held pressure sprayer at 2,500, 8,333 and 25,000 nematodes/ml of each species provided about 60 percent control; this was 20 percent less than the previous season's study. These results would suggest that CW control with parasitic nematodes has practical limitations. However, it is presently the only method other than preventing stress conditions which encourage initial infestation.