Planted-green cover crops in maize/soybean rotations confer stronger bottom-up than top-down control of slugs

Abstract

No-till farming is a conservation agriculture practice employed on over 100 million acres of farmland in the United States. This practice provides benefits ranging from erosion control to pest suppression but can also facilitate outbreaks of novel pests. In the Mid-Atlantic, USA, where no-till production is widely adopted to help maintain the health of the Chesapeake Bay watershed, slugs have become a major pest of no-till row crops. Tillage buries slug eggs and kills all life stages; thus, slugs thrive without this interference in no-till systems. Effective slug control options are lacking, but integrating cover crops into crop rotations, especially when delaying termination until after cash crop planting (planting green), could be an ecologically based, cost effective method to control slugs. Cover crops may offer a dual-pronged approach to slug management, conferring top-down control by creating habitat for predators and bottom-up control by acting as a dietary distraction. The goal of the experiment presented here was to understand how delaying cover-crop termination until after cash-crop planting affects top-down and bottom-up control of slugs. Additionally, we assessed the effect of neonicotinoid-coated seeds on top down-control because insecticides can harm predators. Across three commercial, row-crop farms in Pennsylvania, USA, we found that slug activity-density and damage to cash crops was lowest in planting green treatments due to higher residue coverage and that planted-green maize plots without seed coatings had the lowest slug pressure. Planting-green produced lower yields that, given the conservation benefits, may be acceptable to some farmers, and yields were not enhanced by insecticidal seed coating. Collectively, our results indicate that planting-green can act as a novel, bottom-up management strategy for slugs that functions independently of top-down control.