Insecticide application timing effects on alfalfa insect communities

Abstract

Timing of insecticide application can impact efficacy, given variation in both weather and development of the crop and its insect pests. Both target and nontarget insects may vary in life stage and abundance at the time of application. In alfalfa Medicago sativa L. cropping systems, producers have interest in early-season insecticide applications to eliminate last-minute decisions about preharvest applications for alfalfa weevil Hypera postica (Gyllenhal) (Coleoptera: Curculionidae). The standard recommendation is based on scouting larvae close to the first harvest time. We compared early and standard timing of application of a lambda-cyhalothrin pyrethroid on alfalfa pest and beneficial insects. Field trials at a university research farm were conducted in 2020 and 2021. In 2020, early application was as effective as the standard timing against alfalfa weevil, as compared to the untreated control, but less effective than the standard timing in 2021. Effects of timing against Lygus bugs (Hemiptera: Miridae), grasshoppers (Orthoptera: Acrididae), and aphids (Hemiptera: Aphididae) were inconsistent between years. We observed the potential for early application to reduce negative impacts on ladybird beetles (Coleoptera: Coccinellidae) and spiders (Araneae), however, damsel bugs (Hemiptera: Nabidae) were similarly reduced by insecticide application regardless of timing. Overall arthropod community composition differed by both year and treatment. Future research should explore potential trade-offs of spray timing at larger spatial scales.

Volatiles from cotton aphid (Aphis gossypii) infested plants attract the natural enemy Hippodamia variegata

“…Excessive use of insecticides can lead to increased aphid resistance ( Ma et al., 2019 ; Zhang H. et al., 2020 ), higher pesticide residues in soil ( Hua et al., 2023 ), and harm to natural enemies of insects. The decline of natural enemies can cause a surge in pest populations and disrupt the ecological balance of farmland ( Das and Rahman, 2023 ; Dunn et al., 2023 ; McClure et al., 2023 ; Seni, 2023 ). Hence, it is imperative to prioritize sustainable and environmentally friendly alternatives to chemical control in order to efficiently manage cotton aphids.…”