West central Michigan small fruit regional report – August 18, 2015
Elliot is the main blueberry variety being harvested. A tight spotted wing Drosophila control is critical to maintain fruit quality and yield.
Blueberry harvest is the main topic at this time. Despite the expected decrease in yields due to winter damage, west central Michigan still has a long way to go before blueberry harvest is over. However, there are two issues that are important for most small fruit growers, including blueberry growers: weather and spotted wing Drosophila (SWD).
For the past seven days, the daily average maximum temperature has been 83 degrees Fahrenheit and the minimum around 62 F. In addition, no significant amount of precipitation has occurred during the same period, and only traces of rain have been observed. These weather conditions are affecting all blueberry fields, but they are more problematic for growers with limited irrigation or non-irrigated fields. Blueberries in particular require supplemental irrigation to maintain quality and yield. However, even with some irrigation, some growers are complaining about soft berries at harvest.
So far, fruit quality up until this past week was excellent and yields better than expected. However, at this time it is almost impossible to obtain SWD-free blueberries, so growers need to assess every load of fruit before it is delivered for fresh pack or processing. That monitoring will prevent further complaints about fruit rejection.
If you find SWD larvae in your fruit and need to spray, consider the weather conditions and select the appropriate insecticide accordingly. Remember, if you decide to use an insecticide with a 24 hour pre-harvest interval (PHI), harvesting immediately after the end of the 24 hour PHI does not always result in clean fruit. This is because the insecticide may not have penetrated into the fruit in a quantity large enough to kill large larvae that requires being exposed to a bigger insecticide amount than small larvae.
If you are in the middle of harvest and the number of SWD flies in your trap are high, do not use Malathion unless weather conditions will ensure the product will not be degraded by high temperatures or washed off by rain. Use Mustang Max or any other insecticide with a short PHI. Although you may start harvesting immediately after the 24 hour PHI, it will be better to wait a few hours more to allow more time for the insecticide to act, especially under high SWD pressure. However, if you can wait three or more days to harvest, use Imidan, Lannate, Delagate, Danitol or any of the other recommended insecticides with a three-day PHI. For insecticide options and recommendations, please consult the “2015 Michigan Fruit Management Guide,” Michigan State University Extension Bulletin E0154, or the “SWD Management Recommendations for Michigan Blueberry” fact sheet.