West central Michigan small fruit update – July 12, 2023

Blueberry harvest is in progress. Blueberry maggot and spotted wing Drosophila are already active in fields.

Photo 1. Bluecrop fruit clusters with ripe and green fruit in Allegan County, July 10, 2023. Pollination at this field was affected by flower thrips preventing pollination of the first flowers. Green fruits still growing are affected by high temperatures and drought, which could result in reduced yield per acre. Photo by Carlos Garcia-Salazar, MSU Extension.

West central Michigan remains under drought conditions, with daily minimum and maximum temperatures averaging 51 and 82 degrees Fahrenheit. For the past 15 days, no more than 0.52 inches of rain have accumulated in the area. This amount of rain does not supply blueberry fields with enough water to maintain a healthy crop. Although the spring-summer drought is not as severe as in 2022, its effects are more pronounced in fields with limited supplemental irrigation or fields where growers missed critical periods where irrigation could have made a difference.

Another factor is the variety. Fields with Bluecrop are showing more of the effect from high temperatures and drought conditions. Elliott and other late and mid-season varieties are doing fine with a nice crop and great fruit quality. Fields already in harvest are those planted with Bluetta, Brigitta and other early season varieties.

The harvest of Bluecrop started this week with fruit of excellent quality and flavor at fields where irrigation was applied in a timely manner. There are, however, fields where pollination was affected either by high temperatures or where flower thrips affected the pollination process. The harvest of those fields could be difficult because there are a few leading berries ready for harvest while the rest of the berries in the fruit cluster are still in early stages of development (Photo 1). If growers wait for the rest of the berries to turn blue, blueberries already ripe will lose firmness and quality, and they will become a breeding ground for spotted wing Drosophila (SWD) and blueberry maggot.

Regarding insect pest problems, blueberry maggot and SWD are already active in blueberry fields. Some localized rains occurring over the past days accelerated the emergence of blueberry maggot flies and they already have been trapped in yellow sticky traps at monitoring sites. On the other hand, SWD started arriving in Allegan and Van Buren County blueberry fields. However, SWD numbers are still small, and two-thirds of flies trapped at monitoring sites are overwintering females (smaller and darker than summer flies) with some flies already from the first summer generation (Photo 2).

Photo 2. Comparison between an overwintering SWD female and a fly of the first summer generation. Notice the dark color of the overwintering flies, bottom, compared with the honey color of the summer flies (individual on the upper portion of the picture). Photo by Anna Wallingford and Greg Loeb, Department of Entomology, New York State Agricultural Experiment Station, Cornell University, Geneva, NY.

Large numbers of wild blackberries and raspberries have been found with large numbers of SWD larvae at southwest Michigan blueberry fields. Therefore, growers need to be alert to the presence of SWD if they have fields ready for harvest or more than 5% of the fruit is already in the blue stage.

Photo 3. Diagram showing the decision-making process to decide when and what to spray to control spotted wing Drosophila based on the weather conditions at the target site. Photo by Carlos Garcia-Salazar, MSU Extension.

Table 1 presents some of the recommended insecticides to initiate SWD management. Photo 3 is a diagram showing when and what to spray under different weather conditions.

Table 1. Key insecticides for spotted wing Drosophila control in blueberry and their response to environmental conditions during the application.
Insecticide Class Rainfastness Heat affected Penetration Weather conditions
Rainy, more than 0.5 inch Hot, 90 degree or more
Imidan Organophosphate Low No Limited Reduced activity Excellent
Malathion Organophosphate Low Yes No Reduced activity Reduced activity
Brigade Pyrethroid High No No Excellent Excellent
Mustang Maxx Organophosphate High Yes No Excellent Reduced activity
Lannate Carbamate Moderate No Yes Excellent Excellent
Assail Neonicotinoid Moderate No Yes Excellent Use it
Exirel, Verdepryn Diamide High No Yes Excellent Excellent
Delegate, Entrust WP, Entrust 2SC Spinosyn High No Yes Excellent Excellent
John Wise, Rufus Isaacs, Carlos Garcia-Salazar, Michigan State University Extension 2022.

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