NETTING APPLICATIONS FOR INSECT MANAGEMENT IN APPLE ORCHARDS

Adrian Marshall

Exclusion netting may provide sustainable protection from apple insect pests where chemical control options are limited. To examine the efficacy of net enclosures to exclude direct pests and assess non-target effects, I investigated pest and natural enemy densities in net-enclosed versus open blocks. I conducted trials to assess the effects of large enclosures (48 trees) and small enclosures (three trees). In all studies, results were strikingly similar. Direct pest, codling moth (Cydia pomonella (L.)) and Euschistus conspersus Uhler, abundance and damage were lower inside the enclosures, while the abundance of an indirect pest, woolly apple aphid, Eriosoma lanigerum (Hausman) was substantially higher. The increase in woolly apple aphid densities may be related to the reduced abundance of two important groups of its natural enemies, lacewings and syrphids, inside the cages. These findings indicate that while netting structures may improve direct pest control, biological control services can be disrupted leading to indirect pest outbreaks. I investigated the ability of net enclosures to inhibit migration of codling moth, a key direct pest of apple. Mark-recapture experiments were used to assess the permeability to immigrating and emigrating adults. Moth emigration was reduced only slightly by the presence of the nets (versus controls), but only one moth released outside was recaptured inside the cages. This suggested that the netting is physically permeable to codling moth, but provides a behavioral barrier to external populations. Native stink bugs, also direct pests of apples, frequently migrate from uncultivated land into the orchard borders making them difficult to control. Using clear sticky panel traps, I determined the average height at which stink bugs migrate is from 2-3 m. With this information, I assessed the ability of a 4 m net barrier at the orchard border to exclude stink bugs and found that they reduce stink bug migration into the orchard. Through these studies, I established that net barriers can provide an additional method for direct pest control. Although, the negative effects on indirect pests and natural enemies need to be carefully considered for improving crop protection.

NETTING APPLICATIONS FOR INSECT MANAGEMENT IN APPLE ORCHARDS

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