Grand Rapids, Mich., area small fruit regional report – July 23, 2013
The number of chemical tools for spotted wing Drosophila control is limited and keeping them working for the longest time possible can help growers reduce economic losses and pesticide residues on the fruit.
Blueberry harvest is at its peak for early season varieties like Duke, Bluecrop, etc. There is a very good fruit quality and very good size because of the abundant rains that occurred during the growing period. It is also the time to be alert against the presence of the blueberry maggots, Japanese beetles and spotted wing Drosophila (SWD).
Since 2010, SWD has displaced the other mentioned insects as the main concern for the blueberry industry. SWD has put upside down the whole integrated pest management (IPM) program developed over a decade of basic and on-farm research conducted at Michigan State University and elsewhere.
Different than other crops, the blueberry harvest occurs over a short period of time, leaving little room for errors, especially when dealing with insect pests that affect the quality of the fruit near or at harvest time. Because of this, growers are required to make important pest control decisions in a short period of time to prevent economic losses due to fruit losses or downgrading of the fruit quality.
Some of the most critical decisions at this time are timing of SWD control, selection of the appropriate insecticides and prevention of the development of the resistance of the pest to the current pest control tools. Making an informed IPM decision on those issues is essential to succeed in the control and management of SWD without affecting the current IPM program established on the farm.
Currently, Mustang Max is being used more often than other recommended insecticides to prevent infestations by SWD larvae in blueberries at harvest time because of its short pre-harvest interval. Some growers are already applying the third back-to-back application of this product. However, growers need to realize that back-to-back applications of pyrethroids speed up the development of resistance in SWD to these insecticides. To prevent this, it is necessary to rotate insecticides combining organophosphate and other broad spectrum insecticides recommended. Please consult the Michigan State University Extension bulletin E-154 “2013 Michigan Fruit Management Guide” for a list of recommended products.
Regarding the current situation of SWD populations in west central Michigan, we are observing an increase in the numbers of flies trapped in selected fields that in 2012 suffered heavy SWD infestations. However, the numbers are still smaller than observed in 2012. This might be the result of growers’ awareness of the importance of an early control of this pest to prevent further complications at harvest time, and the intense Extension work conducted by the small fruit team during 2012 and early 2013.
On the status of the SWD on other small fruit crops like strawberries, raspberries and blackberries in west central Michigan, at this time only raspberries and blackberries are at risk. For the most part, strawberries escaped the attack of SWD. However, day-neutral varieties might have a problem later on. We observed the presence of SWD in Ottawa County in only one strawberry field where we found a SWD larva at harvest time, but no flies were captured.
As we enter the blueberry and the red raspberry harvest season in full swing, there are some guidelines growers need to observe to prevent SWD infestations in harvested fruit. This includes:
- Sampling fruit using salt solution. Inspect the fruit before and after insecticide applications to verify the effectiveness of pest control actions. Also, inspect the fruit before taking it to the farmers’ market or to processors to prevent rejections.
- Read and understand the insecticide labels: PHIs, REIs, season limits and residual activity.
- Avoid use of “calendar”-based SWD control. Applications on a calendar basis may result in excessive pesticide residues on fruit, worker pesticide exposure and expensive pest control.
- Warning!!! Use of Pyrethroids on a calendar basis may result in outbreaks of bud mites and SWD resistance!!