Written by Tianna DuPont, WSU Extension, February 8, 2020. A summary of a presentation by Betsy Beers and Kacie Athey, WSU Entomology at North Central Washington Apple Day January 2020.
With increasing codling moth pressure, growers are looking for new management tools. Biological control released by drones is a fascinating possible solution. Betsy Beers and Kacie Athey, Washington State University Entomologists and Nathan Moses-Gonzales, M3 Consulting are working to add Sterile Insect Release (SIR) to your toolbox for codling moth management. Beers spoke about the results of their project at North Central Washington Apple Day in Wenatchee last month.
Beers calls SIR “mobile mating disruption.” The idea is that codling moths (male and female) are irradiated so that they are sterile. A large number are released in order to overwhelm the native population so that many wild (fertile) females mate with sterile males. Females that mate with sterile males produce no offspring, reducing the size of the next generation.
SIR has a long track record. It has been used against several pests since the 1950s, with pink bollworm, a pest which destroys cotton, being recently eradicated. For codling moth, we have a long history to build on. In the 1990s extensive research was done in Wapato and British Columbia. SIR is currently used on about 8,200 acres in Canada as part of an area-wide program where it serves as their main form of control.
WSU SIR – Meeting new challenges
When Beers started to look at sterile insect release, she looked at the biology and thought, “How can we do this compared to the Canadians?” In Washington we already have an IPM program which includes mating disruption, so we have to find how SIR works with current controls. To make SIR successful Beers and her team need to learn what rates are effective, how it can be incorporated in an integrated program with mating disruption and current sprays, and how we can practically release large numbers of sterile moths cost-effectively.
Beer’s experiment is in large, eight-acre, plots between Mallot and Tonasket, WA. Treatments include: a standard similar to the Canadian model where 800 moths per acre were released each week for 22 weeks in addition to grower standard sprays and mating disruption; a second treatment where the rate was increased at peak timing and decreased between generations with standard controls; and the third treatment is a grower standard.
One of the many ways Beers and her crew are re-inventing SIR is doing releases by drone. All moths were released by M3 consulting, a commercial company who now offers SIR release as a service. M3 has developed a system that is ‘gentle’ on the moths. Speed of release should increase the number of sterile moths that make it alive to the field.
Project preliminary results
In 2018 results were what researchers expected with higher captures of moths in the increased rate and lower pre-harvest fruit damage in both the standard SIR and the variable rate SIR compared to the grower standard. In 2019 things looked different. In 2019 the trap catch was lower in both treatments. What made the difference? “The first thing we looked at was the weather,” Beers explained, “But looking at degree days 2018 and 2019 were not very different. We don’t think temperature is the main difference.” In 2019 there were also not significant differences between the treatments. In some blocks, things looked better in 2019. For example, Beers showed a block where in 2018 there was a hot spot that was partially cleaned up in 2019. “This is just the sort of thing we are hoping to see with SIR,” Beers said. But blocks were variable. “We are not sure why we did not see differences in 2019,” Beers said. The next thing they will look at is the spray programs in these blocks. The group hopes that with a third year of this project they will be able to see clear patterns and lessons learned from this project.
SIR Myths and Recommendations
While research is ongoing the first commercial releases started in 2019 with 1200 acres and will go up to approximately 2500 acres released by M3 consulting in 2020. As researchers work out the details, we can still take home a few messages. “A common myth is if I am using SIR I can stop spraying,” said Beers. This was only possible in Canada after many years. “If you are going into your SIR with a screaming pile of moths you can not stop spraying,” Beers reminds us. We think SIR can augment mating disruption and sprays in problem blocks but is likely not a replacement.
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