Insecticides outweigh rye cover crop in triggering secondary pest outbreaks

Broad-spectrum insecticides are extensively used to control pests and secure crop yields. However, insecticides may have unintended effects on natural enemies (e.g., predators and parasitoid wasps) and secondary pests. Cover crops can also be used as part of integrated pest management (IPM) programs to protect natural enemies and avoid secondary pest outbreaks. Yet, some pests can use cover crops as green bridges to colonize the crop. We explored the use of rye in commercial watermelon fields, with three intensity levels employed by growers: (i) no rye, (ii) 1:3 rye-watermelon ratio and (iii) 1:1 rye-watermelon ratio. Then, we tested the combined effects of insecticide programs (conventional vs. threshold-based recommendations) and rye use (present vs. absent) at three research farms over 2 years.

In both the on-farm survey and research-plot trial, rye weakly affected arthropods, with no impacts on cucumber beetles or natural enemies and marginally positive and negative effects on spider mites and melon aphids, respectively. In contrast, conventional insecticide programs in the research-plot trial effectively controlled the main watermelon pest (striped cucumber beetle) but triggered 45.5 and 21.2% population increases in spider mite and melon aphid, respectively, while natural enemies decreased by 82.3% compared to threshold recommendations. Watermelon yield and quality were generally unaffected by treatments.

We show that insecticide practices are more relevant in shaping arthropod dynamics than cover crops in watermelon. Our study highlights the importance of IPM to protect natural enemies, prevent pest outbreaks, minimize costs on unnecessary insecticide applications and enhance sustainable agriculture. © 2025 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.