Grand Rapids, Mich., small fruit regional report – Aug. 13, 2013
Small fruit growers are facing the challenge of season-long spotted wing Drosophila control in raspberries and blackberries.
As populations of spotted wing Drosophila (SWD) continue increasing in late summer and fall caneberries, the main concern for raspberry and blackberry growers is how to keep their crops free of SWD infestations with the small number of chemicals available for pest control without falling into the “Pesticide Treadmill.” Under the “pesticide treadmill” pests become resistant to the effects of pesticides, farmers are required to adopt new and more potent insecticides, to which pests eventually become resistant. Resistance cannot be avoided; it is a natural part of the evolutionary process. The pesticide treadmill often led to further pest problems, putting farmers in a vicious cycle of pests and pesticides, and increasing the burden on the environment.
As of Aug. 13, 2013, the extent of spotted wing Drosophila infestations has increased in almost all of Michigan’s fruit growing areas. Blueberry growers for the most part have been able to maintain a relatively SWD free harvest with a few instances in which their fruit has been rejected or downgraded at the packing plant due to SWD larvae in harvested fruit.
Currently, the harvest of early season varieties like Bluecrop is almost completed in southwest Michigan. However, in counties north of Allegan there are fields that are machine harvested at this time. On the other hand, mid-season varieties like Jersey are in full harvest, and late season varieties like Elliott just started the first hand harvest. So far, early season varieties have escaped relatively unharmed from the SWD attack. However, as the season progresses and the SWD increase, the need for more strict surveillance remains as the main priority for growers to avoid nasty surprises at harvest time.
For blueberries, pest control activities still have a long way to go, more than one month remaining. Therefore, it is necessary to make a rational use of the chemicals available for SWD control to prevent outbreaks of secondary pest problems, pest resistance and avoid excessive amounts of pesticide residues on fruit. The Michigan State University Extension small fruit team has developed a series of recommendations to prevent these problems. For a more complete review of these recommendations, please consult the most recent publication for SWD control “SWD Management Recommendations for Michigan Blueberry” (Isaacs, et al 2013).
For caneberries, the situation is different. Most of the late summer and fall raspberries and blackberries just started harvest. Summer raspberries are finished but late season varieties are ripening at a time when SWD populations are increasing dramatically in all fields, and all small fruit crops. This is a serious challenge for growers trying to maintain their crops free of SWD. This will be especially difficult for fall varieties since their fruit production period extends into November. That is more than three months of continuous pest control actions. Growers need to be vigilant about the presence of the SWD in their fields, and AVOID “Calendar-based” applications of insecticides. There are secondary pests like two-spotted spider mites that are in small numbers in almost all raspberry fields. However, under the right conditions, especially when the insecticides applications eliminate predatory mites, they become a serious pest problem requiring additional chemical control, and increasing the cost of pest control and the amount of residues on the fruit. As in the case of blueberries, the MSU Extension small fruit team has updated the SWD recommendation ““ (Isaacs, et al 2013).