Effects of ground cover treatments and insecticide use on population density and damage caused by Lygus lineolaris (Heteroptera: Miridae) in apple orchards.

We conducted a 2-yr study in commercial apple orchards in Nova Scotia to assess the effects of ground cover treatments and insecticides on population density and fruit injury caused by tarnished plant bug, Lygus lineolaris (Palisot de Beauvois). The design was a split-plot with insecticides applied to whole orchard blocks and ground cover treatments applied to plots nested within orchard blocks. Ground cover treatments were 1) standard herbicide use, 2) enhanced weed control in tree rows, and 3) treatment two plus use of a selective herbicide in laneways. Treatments had few significant effects on vegetation in the tree row, but in laneways, known dicot hosts of L. lineolaris were suppressed and nonhost grasses promoted with treatment 3. Ground cover treatments did not affect cumulative captures of adult tarnished plant bugs on white sticky traps located in the plots but did affect captures in sweep nets. Split-plot ANOVA indicated no significant effect of insecticides on injury in either year, but ground cover treatments were significant in 2001. The lowest ranking rates of injury in both years were in orchards treated before bloom with a pyrethroid insecticide, either cyhalothrin-lambda or cypermethrin. The highest ranking rate of injury occurred in an orchard where insecticide was not applied until after bloom despite a high prebloom capture of L. lineolaris adults on orchard perimeter sticky traps. Fruit injury values for the ground cover treatment 3 were 63.3% (n.s.) and 50.0% (P < 0.05), respectively, of those in the standard treatment in 2000 and 2001.