Peripheral‐zone treatments for plum curculio management: validation in commercial apple orchards

Peripheral applications of organophosphate insecticides were evaluated as an alternative strategy for controlling adult plum curculio, Conotrachelus nenuphar Herbst (Coleoptera: Curculionidae) in four commercial orchards in Quebec, Canada. Each orchard was partitioned into a reference and an experimental plot to compare the classical full plot treatment with a peripheral treatment alternative. The experimental plots were divided into five zones, i.e. central, North, South, West and East. Peripheral zones were defined as the first five rows of apple trees (or 20 m wide). Plum curculio adults were monitored weekly by limb tapping. Fresh oviposition scars were evaluated by examining 20 fruitlets per tree on each outermost tree in the peripheral zone and 20 fruit on 25 trees in the central zone. Azinphosmethyl treatments were carried out in the zones where more than 1% fruitlets bore fresh ovipositional scars. Fruit damage was mostly (92%) found in the peripheral zones. Plum curculio damage at harvest varied from 0.0 to 0.7% and from 0.0 to 0.8% in the experimental and reference plots respectively. Total insect damage on fruit at harvest varied from 1.3 to 3.8% in the experimental plots, and from 0.4 to 5.0% in the reference plots. In 1991, there were no significant differences between population indices of the spotted tentiform leafminer, the apple aphid, leafroller species and cicadellids in the peripheral versus central zones. In the experimental plots, populations of woolly apple aphid, two-spotted spider mite and apple rust mite were significantly higher in peripheral zones than in the central zones. In 1992, there were no significant differences between population indices of peripheral versus central zones for both experimental and reference plots. All localities and years pooled, peripheral zones of experimental plots received 1.22 insecticide treatments, against 1.29 for reference plots. However, central zones of experimental plots received 0.38 insecticide treatments, against 1.13 for reference plots. Assuming a 20 m peripheral zone and a 10 ha square orchard, the percent reduction in insecticides would be ca. 75%.