2017 ASHS Annual Conference

The arid climate of Washington State’s Columbia Basin has caused sunburn to apples for many years. Growers currently use evaporative cooling, kaolin particle sprays, and shade netting practices to combat this damage. Top cover shade netting has become a popular technique in Central Washington, although some have completely enclosed their orchards creating a mechanical barrier to wildlife such as deer, birds, and even insects. These full enclosures could exclude certain insect pests including codling moth, Cydia pomonella, and the invasive brown marmorated stink bug (BMSB), Halyomorpha halys. Conversely, the enclosures may disrupt biological control by also preventing natural enemies. We tested shade net exclusion of pests and natural enemies at a WSU research orchard using four large (4 rows x 12 trees) and twelve small (3 trees) netted cages combined with a conventional codling moth spray regime. These plots were compared with insecticide treated and untreated plots without shade netting enclosure. We used the native consperse stink bug, Euschistus conspersus, as a model organism to determine stink bug exclusion. Pest and natural enemy samples were from naturally occurring populations except consperse, which were from lab colonies and released near the treatment plots. Our results show that codling moth adult densities along with direct pest fruit damage were lower in the cages than in the insecticide treatment and the untreated control. Woolly apple aphid densities were significantly higher in the caged plots, along with its parasitoid Aphelinus mali. Earwigs, an important aphid predator, were more abundant in the small cages, but were not effected in the large cages. Lacewing and syrphid fly capture rates were greatly reduced in the cages compared to uncaged plots. These outcomes suggest that although netting can prevent direct pests, it can also exclude essential natural enemies and lead to the disruption of biological control.