West central Michigan small fruit update – July 10, 2024
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EmailMichigan’s blueberry harvest is in full swing with early varieties already hitting the market. Significant issues are the early arrival of spotted wing Drosophila and Anthracnose fruit rot.
Current Michigan’s weather conditions vary between days with temperatures in the lower 70s and days with elevated temperatures reaching the lower 90s and high relative humidity. These conditions affect the fruit quality and create environmental hazards for farmworkers harvesting under extreme hot weather and high relative humidity.
Another issue, especially in blueberries, is the early presence of insect and disease problems that normally occurs in mid-August. The spotted wing Drosophila (SWD) fly showed up in blueberry fields exceedingly early due to the mild winter and early beginning of the blueberry season, a month earlier than previous years. At the same time, the humid and hot weather conditions and leaky berries in the field due to SWD damage create perfect conditions for outbreaks of Anthracnose and Alternaria fruit rot.
The presence of SWD infestations in blueberries ready for harvest or already harvested has increased substantially. In non-sprayed fields or fields with minimum insecticide applications, fruit damage is already showing SWD eggs and larvae in fruit (Figure 1). At the same time, the numbers of flies per week trapped in monitoring traps is going from only a few to more than 50 flies, with 80-90% being females. Furthermore, in fields already on a SWD spray program, the wet weather this week has washed off residues of insecticides applied before Hurricane Beryl came through Michigan.
In addition, we are seeing blueberry maggot flies in traps and larvae started showing in fruit inspections. It will be important to get back into the fields to protect blueberries from both SWD and blueberry maggot. Michigan State University Extension recommends using effective insecticides with a short preharvest interval. Imidan, Lannate or pyrethroids such as Mustang Maxx, Brigade or Danitol are highly effective. Pyrethroids maintain good activity through light rain. For growers that might find SWD larvae already infesting fruit, a mix of Mustang Maxx and Assail can provide a combined activity against adult flies and larvae. If fields are too wet to enter, border sprays to protect the edge bushes is also an option until the drains can remove standing water.
For Anthracnose infections, Timothy Miles from the Michigan State University Department of Plant, Soils and Microbial Sciences recommends using the fungicide Switch or Abound. However, in places where Anthracnose shows resistance to Aboud, Switch is the best alternative. Do not apply Switch more than two consecutive times and no more than 56 ounces of product per season.
