Enhancing biological control in mating disruption and organic pear orchards by understory management

Habitat management to enhance biological control in cultivated crops is an increasingly common method of pest control in both annual and perennial cropping systems. Examples of this approach include use of windbreaks or hedge rows to prompt build-up of natural enemies around crop edges, planting of insectary seed mixes as cover crops in perennial crops, or management of natural ground cover (e.g., via mowing frequency, strip mowing, or selective herbicide use) to enhance build-up of natural enemies. For all of these approaches, the idea is to provide predators and parasites with alternative sources of habitat, food, or hosts, with hopes that the natural enemies will eventually move into the crop and prevent pest damage. The alternative food sources may include pollen or nectar associated with flowering plants, or arthropods that feed on the non-crop host plants. Ideally, these alternative habitats should not also act as a source of pest insects or diseases, although this can be difficult to attain in practice.

Past-reliance on broad-spectrum insecticides in pear orchards makes it unclear what role the ground cover plays in affecting insect numbers in the orchard. Growers differ in how they manage the ground cover (e.g., in mowing frequency, tilling, herbicide use, tolerance of weeds), and farms differ in the species' composition of ground cover (e.g., in dominance of broad-leaf weeds vs. orchard grass). With heavy use of insecticides, these grower or farm differences are probably inconsequential in affecting insect communities in the orchard. However, with reduced insecticide use, grower differences in ground cover management or farm differences in ground cover make-up potentially have very large effects on the types and numbers of insects occurring in the orchard. These effects may be negative or positive, in that ground cover provides habitat for both beneficial and pest insects.

Objectives of Project

(1) Determine effects of mowing frequency on density and diversity of pest and beneficial arthropods on the orchard floor, in the ground cover, and on the pear tree (summer 1998; results reported here).

(2) Estimate impact of beneficials on pear pests in each mowing regime (i.e., parasitism and predation rates). Some preliminary information provided here; more extensive research on this topic to be conducted in 1999.