Non-target effects of herbicides on Tetranychus urticae and its predator, Phytoseiulus persimilis: implications for biological control.

BACKGROUND

A key element of conservation biocontrol is identifying and limiting the use of pesticides that have substantial non-target effects on natural enemies to prevent biocontrol disruption. The Phytoseiidae (predatory mites) are one of the most studied natural enemy groups in the field of pesticide non-target effects. Although there is substantial research on the non-target effects of insecticides on arthropod natural enemies, research on herbicide impacts is limited. Natural enemies, including phytoseiids, associate with weeds due to the presence of alternative prey, shelter, or floral resources. Therefore, a whole-systems approach to integrated pest management should integrate weed management with biocontrol. We conducted a study to examine the non-target effects of vegetable herbicides on Phytoseiulus persimilis Athias-Henriot, and the primary pest that it controls, Tetranychus urticae Koch. Two assays were used to assess the effects of direct application and walking on residues.

RESULTS

In both assays, S-metolachlor was highly toxic to P. persimilis (80-90% mortality) and had minimal effect on T. urticae. Dicamba, oxyfluorfen, and napropamide also caused moderate levels of P. persimilis mortality (21-74%). Check mortality of P. persimilis was higher in the direct contact assay (19%) than the residue assay (3%).

CONCLUSIONS

Halosulfuron-methyl, flumioxazin, and mesotrione were the most compatible herbicides with biocontrol by P. persimilis, whereas S-metolachlor and napropamide were the least compatible. We also determined that the residue assay may be more useful than direct contact slide-dips for future assessment of herbicide non-target effects. Future efforts should continue to examine the impacts of weed management on natural enemies to better integrate pest management practices. © 2019 Society of Chemical Industry.