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ARS Home » Pacific West Area » Wapato, Washington » Temperate Tree Fruit and Vegetable Research » Research » Publications at this Location » Publication #398387
Research Project: Integrated Approach to Manage the Pest Complex on Temperate Tree Fruits

Location: Temperate Tree Fruit and Vegetable Research

Title: Herbicides harm key orchard predatory mites

Author
item BERGERON, PAUL - Washington State University
item Schmidt, Rebecca

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/17/2023
Publication Date: 5/19/2023
Citation: Bergeron, P.E., Schmidt-Jeffris, R.A. 2023. Herbicides harm key orchard predatory mites. Pest Management Science. 14(5):480. https://doi.org/10.3390/insects14050480.
DOI: https://doi.org/10.3390/insects14050480

Interpretive Summary: Conserving predators of orchard pests is a critical part of pest management. To do this, growers can choose pesticides that are minimally harmful to these predators. There is little information about how herbicides affect pest predators. Researchers at the USDA-ARS laboratory in Wapato, WA and Washington State University tested seven pesticides and five adjuvants for effects on two important pest mite predators. They found that three herbicides either killed the adult predators or reduced their reproduction. Because these harmful herbicides are likely replacements for glyphosate (Round-Up), pest mite outbreaks in orchards could result from their increased use.

Technical Abstract: Background: The phytoseiid mites Galendromus occidentalis and Amblydromella caudiglans are critical for conservation biological control of spider mites in Washington apples. While the non-target effects of insecticides on phytoseiids are well-described, research on herbicide effects on beneficial arthropods is limited. When phytoseiids move from the orchard canopy to the ground cover in search of prey, they have an increased risk of herbicide exposure, especially due to their small size and inability to fly. Using bioassays, we examined lethal (female mortality) and sublethal (fecundity, egg hatch, larval survival) effects of seven herbicides and five surfactants on A. caudiglans and G. occidentalis. The effects of mixing herbicides with recommended surfactants were also tested. Results: Glufosinate-ammonium was the least selective herbicide tested, causing 100% mortality to both species. Paraquat caused 100% mortality in A. caudiglans and 56% mortality in G. occidentalis. Sublethal effects were significant for both species when exposed to oxyfluorfen. Adjuvants did not cause non-target effects in A. caudiglans, but some adjuvants, including a non-ionic surfactant, increased mortality and decreased reproduction in G. occidentalis. Conclusions: The high toxicity of glufosinate and paraquat to both predators is concerning; these are the primary “burn down” herbicide alternatives to glyphosate, which is decreasing in use due to consumer toxicity concerns. However, while glyphosate was relatively non-toxic, alternative products may disrupt biological control. Field studies are needed to determine the extent that herbicides disrupt orchard biological control, focusing on glufosinate-ammonium, paraquat, and oxyfluorfen. Consumer preferences will need to be balanced with natural enemy conservation.