Trade-offs of cover crops for arthropod pest regulation, a meta-analysis

Cover crops provide benefits to farmers and to the environment that include improved soil health, water quality, and weed suppression. However, due to farmer concerns about management complexity, increased labor, uncertain economic returns, and potential for increased pest susceptibility, cover crop adoption remains persistently low in many regions. Numerous extension resources caution that cover crops might increase risks of pest outbreaks by creating “green bridge”, or reservoir harboring crop pests. However, cover crops and living mulches also provide food, habitat resources that support diverse communities of natural enemies and strengthen biological pest control. Here, we use meta-analysis to evaluate risks and benefits of cover crops for both pests and their natural enemies in cash crops. We identify crop system characteristics (perennial and annual, crop families) and cover crop characteristics (terminated cover crops, living mulches, flowering cover crops, cover crop mixtures) that lead to most reliable pest control outcomes. Overall, cover crops reduced pests and enhanced natural enemies, providing little support for “green bridge” effects purported to increase associational susceptibility to pests. In fact, only 27 out of 229 total observations revealed increased pest pressure in cover crop treatments. Pest susceptibility did not increase when cover crops were closely related to cash crops. Cover crops had consistent negative effects on herbivore pests across crop systems, and natural enemy enhancement was stronger in perennial systems relative to annual systems, where greater seasonal disturbance system-wide might limit pool of natural enemies available to respond to food and habitat resources provided by cover crops.