Weather conditions in Michigan’s central region are under a moderated summer drought with limited precipitation that is not enough to satisfy the hydric needs of small fruit crops, especially blueberries. Daily temperatures have been hot with an average minimum of 62 degrees Fahrenheit and a maximum of 84 F.

Apart from the rains occurring Monday, July 11, in the Ottawa and Muskegon counties, which left up to 1.5 inches of rain, drought conditions are prevalent, especially in the southern portion of Allegan County and around the Grand Junction, Michigan, area. As a result of this, blueberries in that area are showing drought stress with fruit shriveling and dropping out of the bushes. That is especially pronounced in fields located in sandy soils. Monday rains that provided some relief to blueberry fields in Ottawa and Muskegon counties did not reach southwest counties. If supplemental irrigation is not provided to blueberry fields in those areas, this summer drought may affect fruit quality and volume of the blueberry harvest.

Blueberries are in harvest in most fields planted with early season and mid-season varieties. Fruit harvested so far is of good quality and yields are good. However, if rain does not occur in the next five to 10 days, drought conditions will seriously affect the second and third harvest.

Regarding insect pest problems at harvest time, spotted wing Drosophila (SWD) had its largest emergence so far in the central region. Populations in one site went from one fly per week to 23 flies in one trap in the Fennville, Michigan, area. High temperatures and scattered rains are creating conditions in the field suitable for SWD reproduction and development.

So far, no fruit damage has been reported in blueberries harvested during the past weeks.

We started catching SWD in red raspberries that just began ripening in the Ottawa/Kent County area. The first infested fruits have been reported. Raspberry growers are already spraying to prevent the buildup of the SWD population. Special attention should be placed on fields in proximity to unharvested strawberries or fields that are not yet renovated. Also, any blueberry or raspberry field next to a wooded area should be monitored frequently since wild hosts are breeding sites for SWD populations that later on will migrate to the crop.

Controlling SWD at this time should be carried out considering the weather conditions in your area. High temperatures or rains affect the effectiveness of insecticides selected. High temperatures tend to affect the longevity of insecticide residues on the plant or reduce their toxicity. In other cases, high temperatures increase the lethality of the insecticide. For example, Brigade exhibited an increased toxicity with an increase of temperature within the 60 to 98 F range. In that temperature range, it was reported to be up to 2.8 times more toxic than at low temperatures. Conversely, Mustang Max in the same range was five times less toxic than at lower temperatures, according to Boina et al 2009, Journal of Economic Entomology. However, the three-day pre harvest interval for Brigade in blueberries should be considered when selecting this insecticide versus applying Mustang Max, which has a one-day pre-harvest interval. If you are not harvesting immediately, Brigade will be a good choice, as will the organophosphate (OP) Imidan. Brigade behaves as an OP insecticide at high temperatures in the same manner as Imidan.

Michigan State University Extension recommends that before making a determination about what insecticide to apply, growers visit the MSU Enviro-weather website to check for current weather conditions and extended weather forecast for their location. Selecting the best insecticide according to weather conditions will minimize the risk of SWD control failures due to insecticide inactivation by high temperatures or rain. For a complete list of recommended products and doses, consult MSU Extension’s “2016 Michigan Fruit Management Guide” (E0154) or call your local MSU Extension office for assistance. You may also contact me at 616-260-0671 or garcias4@msu.edu.