MSU Extension

Weather conditions in central Michigan remain under moderate drought with daily temperatures reaching the mid-90s. Average maximum daily temperatures during the past seven days were 86 degree Fahrenheit and the minimum averaged 64 F. There was some relief from the drought conditions by a series of rain showers and thunderstorms that left around 2.5 inches of rain in the area. That rain was a much needed help to diminish the drought impact on small fruit crops, especially blueberries.

Raspberry harvest continue with problems related to spotted wing Drosophila (SWD). Growers are applying insecticides and populations so far remain under control. Narrow rows of plants and SWD monitoring are helping to maintain a good SWD control.

There are also a few day-neutral strawberries that are being harvested, and the fruit quality is excellent. However, SWD is already showing up on strawberries that are in our SWD monitoring network, but no SWD-infested fruits have been found.

Blueberry harvest of mid-season varieties continues with some fields in southern counties starting hand-harvesting Elliott blueberries. There are multiple reports of SWD fruit infestations. Growers are finding their fruit contains SWD larvae when their loads are evaluated at the packing facility.

On the other hand, SWD control is more problematic for U-picks. Because of the restrictions on the use of some insecticides in U-pick operations, they are having problems with insecticide sprays because of the need to close for one day or more in order to use some of the most effective insecticides to control SWD infestations. For those growers, closing one day represents losing income and clientele. For this type of operation, harvesting clean, all ripe fruit is the best management tool. This will limit the availability of fruit for SWD ovipositions.

It is important for all growers to check their SWD traps for the presence of flies. Reduce the trap checking interval from twice a week to once a week if you are actively harvesting, and take immediate action as soon as the flies are observed in the trap. Also, check the fruit for the presence of larvae using the salt test before you harvest. That will prevent bad surprises when the fruit is evaluated at the packing facilities.

Using the salt test to sample for SWD larvae in berries:

• Place about 1-2 cups of fruit in a gallon Ziploc (or similar) bag and lightly crush the fruit.
• Mix up a saltwater solution that is one part salt to 16 parts water (e.g., 1 cup salt in 1 gallon of water) and add enough saltwater solution to the bag to cover the berries.
• Seal the bag, removing as much air from the bag as possible.
• Let the bag sit for at least 30 minutes, then place the bag against a dark surface in good lighting to look for larvae that may have emerged from the fruit.

Another recommendation for controlling SWD is making the right choice about insecticides you are using against SWD at this time. It is necessary to consider the current weather conditions, especially daily temperatures and the presence of rain. During the past week, temperatures in southern counties reached the mid- and upper 90s, and most insecticides are affected by high temperatures and sunlight. Before making the decision to spray, check the weather conditions for the next 24-72 hours via Michigan State University’s Enviro-weather and select the appropriate insecticide accordingly.

In raspberries and blackberries, recommended insecticides effective against SWD at this time are: Brigade 2EC (three-day pre-harvest interval), Delegate 25WG (one-day pre-harvest interval), Malathion 8 F (one-day pre-harvest interval) and Mustang Maxx (one-day pre-harvest interval, see the label for dose). For a complete list of recommended insecticides and doses for SWD control, check the “2016 Fruit Management Guide,” MSU Extension bulletin E0154.

For blueberries, if you are actively harvesting, the recommended insecticides effective against SWD at this time are: Brigade 10 WSB (one-day pre-harvest interval), Mustang Maxx 0.8 EC (one-day pre-harvest interval), Delegate 25WG (three-day pre-harvest interval) and Malathion 8 F (one-day pre-harvest interval). If you are more than three days from harvesting you may use Lannate or Imidan.

For a complete list of recommended insecticides and doses for SWD control, consult MSU Extension’s “2016 Michigan Fruit Management Guide” (E0154) or contact your local MSU Extension office for assistance. You may also contact me at 616-260-0671 or garcias4@msu.edu.