Looking for more pollinator-safe insecticides

A University of Saskatchewan student says red clover could be more widely used if weevil problems can be resolved

Red clover crops in Saskatchewan currently find themselves in a precarious situation. They are one of the most important crops for replenishing nitrogen and organic matter in the soil, but they are also often infested with a serious pest, the lesser clover leaf weevil.

Currently, only one pesticide can eliminate the pests while not being too harmful to pollinators, which, in time, could lead to the weevils developing a resistance.

As a self-incompatible plant, the health of pollinators is important to clovers. They need a high number of pollinators to successfully bloom and produce seed.

University of Saskatchewan master’s student Dan Malamura is conducting research to find an alternative insecticide that will kill weevils while not being catastrophic to pollinator communities.

“Let’s put it this way, all insecticides are toxic to pollinators to some extent because it’s supposed to kill living, flying or crawling organisms,” says Malamura. “But the toxicity of different insecticides varies a lot, especially to pollinators. The one that is registered right now is quite toxic (to pollinators) compared to the ones we are testing.”

Malamura says in the laboratory they are testing potential new insecticides only on bumblebees because they are “commercially available and among the best pollinators.”

However, in field tests all native pollinators that they find in their traps are subjected to the insecticides and tested.

“We found over 12 bee species in our traps and we are assessing all of the pollinator community in our red clover fields,” says Malamura. “But bumblebees tend to pollinate clover the best because they start working earlier and finish later.”

Malamura says more tests still need to be done on the impacts of their insecticides on pollinator populations but the preliminary results have been promising.

“Both of (the insecticides tested) significantly reduced the number of weevil larvae in 10 days,” says Malamura. “What we found based on our traps is some bee species are more vulnerable (to the insecticides) than others. However, it did not have a significant effect on the average number of bees overall.”

The second part of Malamura’s study is looking at the optimal seeding rates for nitrogen fixation and seed production. These tests are being done in multiple locations including the Livestock and Forage Centre of Excellence near Saskatoon, and on Agriculture Canada land near Melfort, Sask.

“There is only one recommendation for optimal seeding rate for a particular soil type and the last paper that was looking at seeding rates was published like 30 to 40 years ago,” says Malamura. “And as I said, many farmers are turning to organic farming systems so they cannot apply nitrogen fertilizer. So they need a nitrogen-fixing crop and among those red clover and alfalfa are the best.”

Malamura is in the second year of his three-year study. When it is complete, he hopes to give farmers the best recommendations for how to grow clover.

“In a perfect world by the end of my work, I plan to give the optimal seeding rate for both seed production and nitrogen fixation, as well as the alternative insecticide for controlling lesser clover leaf weevil with lower harm to bee communities,” says Malamura.

“I hope more organic farmers as well as conventional farmers will choose red clover to increase organic matter and nitrogen fixation because that matters a lot. It holds moisture better in the soil and red clover also attracts more pollinators. Overall, it contributes to sustainable farming and agronomy.”

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