Blueberry Insect Scouting Report for August 5-11, 2012

Large increases in spotted wing Drosophila catches.

Harvest is nearly complete over much of southwest Michigan, and this will be our last blueberry insect update for this season. We hope you found these reports a useful aid for insect management on your farm and hopefully we’ll see you at meetings this fall and winter.

Crop stages

Harvest is almost over in southwest Michigan as most varieties have been picked for the last time and harvest of the late season cultivars, Liberty, Aurora and Elliot are also nearing the end. Harvest should be complete across most of southwest Michigan in the next seven to 10 days.

Weekly insect pest report

Another substantial increase in the number of spotted wing Drosophila (SWD) caught in yeast-baited traps occurred over the last week. This is likely happening because harvest is ending and most fields we scout are no longer receiving insecticide treatments. The proportion of males (identified by distinctive dots on their wings) we have seen in SWD monitoring traps is increasing. The number of SWD in traps will continue to increase over the next several weeks as harvest draws to a close and the predicted cooler temperatures in the 70s and 80s are preferred by SWD.

Until the end of harvest, fields with ripe fruit will still need to be protected with insecticide to prevent SWD infestation. Growers and consultants should keep in mind that unsprayed, un-harvested fields next to fields that are waiting to be harvested may quickly become a source of SWD infestation, and these un-harvested fields may need to be treated before all other harvest is complete. Somewhat cooler weather this week should bring about an increase in SWD activity. We have not found SWD larvae in the fruit samples we have taken from the farms we visited and tested using the salt test method. However, we have received reports of SWD larvae in harvested fruit from other commercial blueberry and raspberry farms. With the increasing frequency of rain, it is important to remember that residue wash off is likely to render fields unprotected from SWD, so reapplication is very important for maintaining protection against SWD.

We are not recommending any sprays for this pest after the last harvest as there is no evidence that this will reduce SWD pest pressure next year. Additionally, it will increase the potential for development of resistance to pesticides. We are starting a research project to determine whether post-harvest sprays will be an effective way to reduce SWD populations and limit SWD infestation. Results of that study will not be available until next season.

A few blueberry maggot flies were trapped last week at farms in southwest Michigan. Insecticides used for SWD control are also likely to control blueberry maggots, but growers and scouts should still be checking traps until the end of harvest. For more information on monitoring and controlling blueberry maggots, including pictures of traps and pictures of the pest, see the MSU Blueberry Facts website or a previous article in the June 21, 2011, Blueberry IPM Newsletter.

Very few Japanese beetles were found in the fields we visited last week. As harvest and insecticide applications slow down at the end of the season, we will likely see an increase in beetles in and around fields after harvest. Read more about Japanese beetle at blueberries.msu.edu.

Lastly, if you have not done so already, take a few moments to note where you had insect concerns this season, so that you can prepare for insect management in future years.

Dr. Isaacs’ work is funded in part by MSU‘s AgBioResearch.

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