It’s that time of year again when spotted wing drosophila (SWD) trap catches begin to rise and cherry growers start to implement spray strategies.
However, Michigan State University Extension Educator Dave Jones says growers wait too long and rely too much on trap catches to make the spray decisions, instead of using disease management strategies to determine preventive sprays. Growers must spray for SWD at yellow cherry fruit, he says.
“We need to realize our crop is in danger from the moment it turns yellow and we need to take appropriate action. We need to spray every seven days and we need to spray regardless of the number of flies caught in the traps until harvest is over,” he writes.
He says trap numbers help give insight on what the fruit fly is doing and where the pest is in the orchard. However, it does not help determine the risk to the orchard.
“In the three conventionally managed tart cherry blocks where we detected larvae in fruit this season, none had the highest SWD counts in traps the weeks that larvae were found in the fruit,” he writes. “One site was actually the lowest the week larvae were detected. The other two sites were in the middle of the pack.”
Jones says the numbers for SWD in July were higher than anything previously recorded at this point in the growing season, which could be the new normal in the state.
“The sad reality is that SWD is so-well established in Michigan at this time that all blocks are at risk once yellow fruit is present, regardless of population counts,” he concludes.