Influence of cover crops on overwintering mortality and spring egg deposition of navel orangeworm

On-farm habitat diversification can positively influence a variety of ecosystem services to agriculture, including biological control of pests. In orchards, many studies have shown that cover crops can have impacts on multiple ecosystem services, such as pollination and pest management. However, few studies have focused on the use of winter cover crops to enhance pest control in almond orchards. The key arthropod pest of almonds in California is the navel orangeworm, Amyelois transitella (Lepidoptera: Pyralidae), which overwinter as larva on remnant nuts, many of which remain on the orchard soil surface. Here, we conducted a 2-year experiment to evaluate the influence of two winter cover crop mixtures on overwintering mortality and spring egg deposition of A. transitella. Remnant nuts placed into cover crop plots produced fewer adult A. transitella in the spring, suggesting increased overwintering mortality. Spring egg deposition was also reduced on remnant nuts in the cover crops, possibly due to the ground covers interfering with host location and access. As such, winter cover crops appear to contribute to the reduction of A. transitella populations in the orchard, although more studies are needed to document specific mechanisms.