Feb 28, 2023
Is Your Pest Protection Washing Away?

Delegate® WG Insecticide, with Jemvelva™ active, Performs Well in Michigan Rainfast Studies 

(Sponsored) Concerned that rainfall could increase the chance of pests damaging your tree fruit, even though you recently treated with an insecticide? 

How well your insecticide fares during a rain depends both on how much precipitation occurs and the active ingredient’s susceptibility to wash-off, according to recent Michigan State University studies. 

The studies rated the rainfast qualities of several active insecticide ingredients on apples and tart cherries. Results show in general that organophosphates are the most sensitive to wash-off, whereas spinosyns, pyrethroids and diamides are more rainfast. Neonicotinoid surface residues are sensitive to wash-off, but subsurface residues are not. 

The studies show that several compounds, including spinetoram, the active ingredient in Delegate® WG insecticide, with Jemvelva™ active, continue to provide plant protection despite rain showers. 

Rainfall of less than one-half inch caused little, if any, product loss from fruit or leaf tissue, says John Wise, Michigan State University entomologist. 

Studying insecticides used in apples and tart cherries, Wise analyzed fruit and leaf tissue to determine insecticide loss due to rainfall. 

Apples treated with Delegate® WG insecticide, a spinosyn, had negligible loss with less than 1 inch of precipitation. 

In the study, a product loss of 30% or less was considered highly rainfast. A moderately rainfast rating was given if product loss remained below 50% and a product loss of 70% was given a low rainfast rating. 

Overall, Delegate applied to fruit and leaf tissue was rated highly rainfast to a half-inch or less of rain. When rain totaled 1 inch, Delegate was rated as highly rainfast on fruit tissue and moderately rainfast on leaf tissue. Even with a 2-inch rainfall, Delegate maintained a moderate rainfast rating on fruit tissue. 

“This is commonly seen with spinosyns that tend to be more rainfast on fruit tissue than leaf tissue. With 1 inch of rain, which is a substantial rainfall, there was minimal product loss on fruit tissue,” says Wise. 

Wise’s bioassay studies also found a significant effect of rainfall wash-off only when precipitation surpassed 1 inch. He attributes the continued pest protection to the binding affinity of spinosads (Delegate) to fruit tissue. 

A second tart cherry study with spotted wing drosophila demonstrates a similar rainfast pattern. 

“With spinetoram or Delegate, there’s sensitivity to wash-off on leaf tissue at the higher rainfall amounts, but not so much on the fruit tissue,” Wise says. “There was a statistical loss in protection at the higher rainfall levels, but not as dramatic as some of the other compounds we tested. That matches the rainfast data we saw in the apple study. The product is persisting on the fruit.” 

Bioassay data reveals significantly more spotted wing drosophila larvae collected per cherry in the untreated check, no matter the precipitation amount. Significantly fewer larvae were documented in the trial for Delegate. 

“Left untreated, spotted wing drosophila larvae didn’t care if there was simulated rain or not. We collected at least 30 to 40 larvae per fruit whether there was zero, half inch or 1 inch of rainfall,” Wise says. 

Wise also examined the potential differences between a 1-inch rain falling in an hour or a day. 

“We varied that factor in a number of studies using the university’s rainfall simulation chamber and did residue analysis,” he says. “We did not find that the intensity or the duration of the rainfall event had a major effect on product wash-off.” 

He also looked at the role of surfactants in insecticide wash-off. 

“Many surfactants improve the end result of residue remaining after a precipitation event, but the data suggests that it is not necessarily that the surfactant directly inhibited wash-off. In many cases, it may simply increase the deposition because the surfactant treatment began with a lot more residue than the comparison without surfactant,” he says. 

Contact your local Corteva Agriscience representative or visit DelegateWG. Corteva.US to learn more about how Delegate® WG insecticide can protect your fruit crop against yield-robbing pests. 

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