Saskatchewan Forage Seed Development Commission - Regina

Demonstration of night spraying technology for control of lesser clover leaf weevil, Hypera nigrirostris (Fabricius) in single cut red clover, Trifolium pratense L. grown for seed production in Saskatchewan.

On June 21 and 22, 2021, the forage seed growers of Saskatchewan hosted an On Farm Experiment field demonstration of the use of night spraying technology as a risk management strategy for control of the major insect pest of red clover grown for seed production in Saskatchewan, the lesser clover leaf weevil (LCLW).

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Two growers from the northeast region were granted access to their single-cut red clover seed production fields to demonstrate autonomous spraying and impact on pollinators and seed yield. Conditions were well suited for the day and night applications of deltamethrin (Decis), the only registered product available to forage seed growers in Canada to control the insect pest. With the lifting of outdoor group size restrictions consequent to the pandemic, many growers attended the Bug and Tech talks for the night spraying demonstration featuring a field robot, a Saskatchewan invention known as DOT, sold to Raven Industries, Emerald Park, SK and rebranded as OMNiPOWER. The robot was the power platform for the CONNECT PLU sprayer made by Pattison Liquid Systems. Lemberg, SK. Sampling for the LCLW was done pre and post-timings of day and night spray applications and compared to the non-sprayed treatment (UTC). The two fields were treated as replicates of the demonstration and a harvest area of about 5 acres was harvested from each of the three treatments for each field. Pollinator traps (blue vanes and bee bowls) were set up in each treatment.

Both fields had moderate to high levels of LCLW adults and larvae. Day and night spraying had an impact on the adults and the larvae, even though Decis acts on contact with the insect. The data gathered from the demonstration, while not statistically significant due to sample size and field variability, indicate the night spray application did no harm to the pollinators, and interestingly, for insects and spiders collected in the traps and grouped as By-Catch, more insects were recorded in the night spray treatment compared to the daytime application of Decis. The day spray improved yield by 11% in Field 1, and 129% in Field 2, compared to the UTC. The differences in seed yield with night spraying were substantive, an increase of 60% in Field 1 and 133% in Field 2 compared to the UTC. The reasons for this major increase cannot be fully explained by the data collected, however, it must be noted that the weather conditions of unusually high temperatures during flowering time and below-average precipitation, likely had a major role in determining seed yield, including impact on the insects and pollinators.