Ecological management of arthropod pests of horticultural crops: lessons from the Central Coast of California

Options for managing arthropod pests of horticultural crops using ecological principles are determined by the behavior of the pest, the availability of environmentally sound suppression tools, including biological controls, and the type of damage the pest inflicts.   The use of appropriate monitoring and scouting programs to detect pests and evaluate the development of infestations is the foundation of any ecologically based pest management program.  Among the most difficult arthropods to suppress on California’s Central Coast are soil pests, such as symphylans, collembolans, and root maggots.  As a group, these arthropods are neither good candidates for biological control, nor easily suppressed with softer insecticide chemistries or crop rotations.  Each crop is attacked by a suite of pests during the course of its development.  Members of a crop’s pest complex may differ in their susceptibility to natural enemies.  Similarly, insecticides that have a preferred environmental profile and that are compatible with some degree of biological control may be available for some pests of a given crop but not others.  The use of broad spectrum insecticides to suppress one pest may disrupt biological controls for another pest on the same crop.  For example, the use of broad spectrum insecticides to suppress Lygus hesperus in strawberry in California can flare infestations of spider mites by killing their natural enemies.  Spider mites are major pests of strawberries, and can be managed with a combination of releases of predatory mites and application of selective acaricides.  Organic strawberry growers rely entirely on natural enemies to suppress mites.  Reliance on the suppressive activity of natural enemies is perceived as too risky by many conventional growers, while conservation biological control is essential for pest management in organic production.  Nasonovia ribisnigri, a lettuce aphid, infests the inner leaves of the lettuce head where few natural enemies other than syrphid larvae are effective.  Conventional growers rely on swift suppression of infestations using systemic and contact insecticides.  Organic growers allow infestations to become established and rely on syrphid larvae to eliminate aphids prior to harvest.  Many organic growers on California’s Central Coast plant insectary crops such as sweet alyssum to provide floral resources to natural enemies with the intention of enhancing their activity.