Orthene (acephate) is a broad spectrum-organophosphate insecticide that has been available to the cranberry industry for many years, but usage of the material in Wisconsin has been low in recent years due to the popularity of Lorsban (chlorpyrifos), another broad-spectrum organophosphate. Lorsban is no longer permitted for usage in cranberry, and this combined with the recent re-emergence of the blunt-nosed leafhopper in Wisconsin has led to a renewed interest among growers in pre-bloom acephate applications. Acephate is only available for a single application per season prior to bloom, so this material has been among the most commonly considered as a replacement for Lorsban across the Wisconsin industry due to its niche in terms of timing and broad spectrum of control. However, some growers cite observations from 25+ years ago that acephate usage appeared to be associated with a reduction in pollinator activity and poor subsequent yield. These historical concerns have led to recent grower interest in investigating whether these same patterns are observable under modern production conditions. Growers are interested in using acephate again, but only if it can be consistently demonstrated that it does not have a negative impact on pollinator activity and subsequent yield.
To help address these concerns, the WI Ocean Spray Ag Science team conducted a 2-year study to test 1.) is a modern grower-standard Orthene (acephate) usage pattern associated with a measurable reduction in pollinator activity? 2.) is this usage pattern associated with a measurable reduction in yield? 3.) Is there consistency in pollinator activity and yield data following a grower standard Orthene application across multiple seasons?
Approach: A grower cooperator made full bed applications of Lorsban at the maximum labelled rate to three beds approximately 2 weeks prior to the arrival of bees in both 2020 and 2021. The grower cooperator applied Orthene 97 at the maximum labelled rate to three separate beds at the grower standard time of approximately 2-3 weeks prior to the arrival of the bees in both seasons. Six one-meter square pollinator observation plots per bed were established, with pollinator counts made three times in each plot during bloom for two years. Honeybee and bumblebee activity was observed three times during bloom in all six beds in both 2020 and 2021. On each observation date, all visits to a flower by any species of bee lasting more than two seconds were counted in each observation plot for two minutes by two researchers counting the same position in an Orthene-treated and Lorsban-treated bed simultaneously. Each visit of more than two seconds to any flower was counted, regardless of whether it was the same or a different bee making each visit during the counting period. The two researchers started the timer for each of the two-minute measurements at the same time to eliminate differences attributed to environmental factors during counts. Counts were conducted between 9AM and 5PM when wind speeds were under 10mph and the sky was not overcast.
Results: Orthene did not significantly reduce pollinator activity in 2020 or 2021. Similarly, there was no significant difference in yield between Orthene and Lorsban treated beds in either year. This was consistent with results recorded by Leroy Kummer and Tim Dittl of Ocean Spray in the 1990s while conducting similar work.
Discussion: There are several possible explanations as to why acephate usage may have been associated with adverse effects on pollinator activity and yield 25+ years ago but that these observations have not been replicable in recent years under modern production conditions. One possible reason for the difference is increased water carrier volumes in modern applications – most growers apply at least 20-25gpa through the boom today compared to significantly lower water carrier volume application by other means 25+ years ago. A highly concentrated solution of any pesticide can sometimes be more associated with adverse effects than a less concentrated solution. Growers today are also well informed and cautious in timing pre-bloom organophosphate sprays, generally placing them 2-3 weeks prior to the arrival of bees on the marsh. It used to be more common to push pre-bloom applications of bee-toxic materials closer to the bloom window than is acceptable today, so it is possible that an acephate application were pushed closer to bloom (less than 2 weeks to the arrival of bees) would have resulted in a negative impact in this study. Finally, formulations change, and modern formulations of acephate (including Orthene 97) have been formulated to have a reduced odor compared to older formulations. It is possible that an older (and higher odor) formulation of acephate may have been somewhat repellent to bees. There are other possible explanations, but some combination of these three variables may be at least partially explain both historical grower observations and this more recent research. In general, this work demonstrates that a modern formulation of acephate used at a grower standard timing (2-3 weeks prior to arrival of bees) and with 20-25gpa of water carrier appears unlikely to have an adverse effect on pollinator activity and subsequent yield.
Acephate has systemic and translaminar properties, and uptake by the plant is fastest during warm, sunny weather. While Lorsban was a strong contact killer of insects, the preferred mechanism for kill with acephate is through ingestion. As with other insecticides that work best through ingestion this means that thorough coverage is helpful to achieve best results, so a high water carrier volume (25gpa+ if possible) is suggested. Acephate’s half-life (the time it takes 50% of the applied active ingredient to degrade) in cranberries is not well studied, but in other crops where it has been studied a half-life as short as 7 days has been observed. This serves as a general reminder that although the product will move into the cranberry plant following application, the active ingredient still degrades over time even though it is more resistant to wash-off from rain or irrigation. This means that like any other insecticide, an application of acephate may not achieve acceptable kill if applied too early and needs to be made based on specific insect population data collected on the farm each week. There has been some anecdotal observation of secondary pest resistance historically, including reported observations of reduced sensitivity in spiny looper populations. Consult with your scouting service following an application of acephate to check that kill of various caterpillar species has been thorough. Growers are also advised to check with their beekeeper if they plan on using any formulation of acephate this year, as well as to consult the mandated usage patterns of their respective handler.This article was posted in Cranberry, Insects and tagged acephate, Cranberries, Insecticides, orthene, pollinators.