Non-target potential of neonicotinoid and fungicide seed cane treatments on Solenopsis invicta

Authors: Penn, Hannah; White, Paul; WILSON, BLAKE - Louisiana State University Agcenter; Richard, Randy

Submitted to: Crop Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/6/2023
Publication Date: 5/9/2023
Citation: Penn, H., White Jr, P.M., Wilson, B.E., Richard, R.T. 2023. Non-target potential of neonicotinoid and fungicide seed cane treatments on Solenopsis invicta. Crop Protection. 170(106278):1-11. https://doi.org/10.1016/j.cropro.2023.106278.
DOI: https://doi.org/10.1016/j.cropro.2023.106278

Interpretive Summary: Normally, Louisiana sugarcane is planted using whole plant stalks. Recently, growers have increased planting stalks cut into short pieces called billets, which allow them to plant with machines rather than by hand and to use plants that were knocked over in storms or are growing crooked. But using billets makes the seed cane more likely to be hurt or killed by diseases and pests, hurting stand counts and yield. To prevent this, billets may be treated with chemicals that may also accidentally kill non-pest insects. The red imported fire ant is one of the most important non-pest insects in Louisiana sugarcane as they eat the sugarcane borer, a major pest. We tested if certain billet seed treatments harm the fire ant and other important non-pest insect groups. In one of two large field tests, we found that the number of fire ants can be reduced by certain insecticide treatments. In three small field tests, we did not see any treatment differences in fire ant or other non-pest insect amounts or how much in how much they controlled sugarcane borers. In the lab, we did not find any differences in the ability of fire ant workers to find food after being exposed to treatments for two days; but the level of ant death changed based on the treatment type and how it was applied (soil sprays or soaked seed pieces). Overall, the seed treatments that we tested may not greatly harm non-pest insects in the field or reduce their ability to eat and control insect pests, but they should be further studied given the potential harm to fire ants.

Technical Abstract: Traditionally, Louisiana sugarcane has been grown vegetatively from whole stalks, but innovations in machinery and rising labor costs have increased interest in billet planting. Billets, short stalk pieces containing several viable eyes, are more susceptible to pathogen exposure and may require fungicide and/or insecticide applications at planting to increase stand potential. Work in other crops indicates such treatments may alter arthropod predator abundance, so the goal of this study was to evaluate the potential non-target effects of select treatments at planting on the red important fire ant (RIFA), Solenopsis invicta, and other arthropod predators of the sugarcane borer, Diatraea saccharalis, in sugarcane. We sampled predators and measured biological control potential in plots treated with a neonicotinoid insecticide and/or fungicide applied as in-furrow sprays or seed cane dips. We then assessed RIFA worker survival and behavior following 48 h exposure in the laboratory. With the exception of one in-furrow sprayed field trial, treatments did not significantly impact RIFA numbers. Treatments did not impact the abundance of other predator groups or biological control potential (borer damage and sentinel egg predation) in any field trial. Laboratory assessments indicated no treatment effect on RIFA behavior metrics after exposure but had mixed results on survival depending on application method. Our data indicate that these seed cane treatments may not disrupt biological control and the greater epigeal arthropod predator community in Louisiana sugarcane. However, tests should be replicated under different environmental conditions to ensure biological control, particularly by RIFA, is maintained with larger-scale use.