Impact of groundcover manipulations within windbreaks on mite pests and their natural enemies

Non-crop vegetation adjacent to broad-acre pastures and crops can influence the abundance of invertebrate pests by promoting populations of beneficial natural enemies. However, characteristics of adjoining vegetation that consistently promote natural enemies are often unknown. Here we manipulate the height of grasses and herbaceous plants within windbreaks at five geographically separated sites in south-eastern Australia to examine the effects of on-ground vegetation structure on the abundance of pest mites and natural enemy complexes. Reducing the height and cover of vegetation across 2 years led to decreased numbers of predatory mites, predatory beetles and spiders within windbreaks and at sites 5 m from the windbreak edge within adjacent pastures. There was also an associated increase in numbers of pest earth mites, the redlegged earth mite (Halotydeus destructor) and blue oat mites (Penthaleus spp.). Similar findings were found in manipulative experiments under semifield conditions using microcosms. These results suggest that an increase in height and perhaps complexity of groundcover act to promote populations of beneficial natural enemies with potential suppression of pest mite species. These findings point to a simple way for increasing populations of beneficial invertebrate species at the farm scale that could contribute to integrated pest management programs.