Ground beetles suppress slugs in corn and soybean under conservation agriculture

Conservation agriculture practices such as eliminating tillage and planting high residue cover crops are becoming increasingly important in field crop systems in the US Mid-Atlantic. However, these practices have sometimes been associated with an increase in moderate to severe damage to field crops by slugs. Conserving natural enemy populations is a desirable way to manage slug infestations because remedial control measures are limited. Here, we tested the effects of conservation practices, weather, and natural enemies on slug activity-density measured by tile traps placed among 41 corn and soybean fields during the spring of 2018 and 2019 in the Northern Shenandoah Valley, Virginia, USA. We found that a positive effect of cover crops on slug activity-density was reduced by tillage and that slug activity-density declined with increasing ground beetle activity-density. Slug activity-density also declined with decreasing rainfall and increasing average temperature. Weather was the only significant predictor of ground beetle activity-density, which was reduced in sites and weeks that were relatively hot and dry or that were cool and wet. However, we also found a marginally significant negative effect of pre-plant insecticides on ground beetles. We suggest that the observed interacting effects of cover crops and tillage reflect favorable conditions for slugs provided by increased small grain crop residue that can be mitigated to some extent by even low levels of tillage. More broadly, our study suggests that implementation of practices known to promote recruitment of ground beetles in crop fields can improve natural suppression of slugs in corn and soybean that are being increasingly cultivated according to conservation agriculture practices.