Spotted wing drosophila (SWD), Drosophila suzukii, is a serious pest of many different fruit crops including caneberries, blueberries and cherries. Ever since its introduction into the United States in 2008, it has been an increasingly severe problem for many growers. Blueberry growers that at one time would perhaps apply insecticides once per season to control leafrollers must now make regular applications every 7-10 days beginning with fruit ripening up until harvest in order to control SWD. This increase in pesticide applications has had many negative consequences for growers. For those who sell to other countries, particularly our biggest export markets- Japan, Taiwan and Korea, this has been an especially big challenge. Different countries often have different amounts of pesticides they will tolerate on produce, and some won’t even allow any residues of certain chemicals to be present. This can be a problem when growers from the U.S. try to export their produce, because while they are within chemical residue limits for the U.S., if they are found to be above tolerances for the country they are exporting to, their produce will be rejected. In addition to increased difficulty in controlling pesticide residues, increased applications of pesticides can also reduce fruit yield because applying pesticides requires growers to drive through their fields more often with heavy machinery, which tends to knock berries onto the ground. This can be particularly severe near harvest, when the branches of blueberries are heavily laden with fruit.
Some blueberry growers, especially those with valuable late season varieties, have installed misters in their fields. These are designed to cool the blueberries and reduce sun damage by emitting a fine spray of water. They could also be used to apply pesticides, an application method which we are coining mistigation. There are several potential benefits to switching to this method of application. Growers would not be required to drive heavy spray machines and tractors up and down their rows to make a pesticide application, and therefore would not be knocking as many berries to the ground. Mistigation could also decrease the amount of time and money required to apply pesticides because an application would simply require the grower to put the pesticide into the mistigation system, turn on the water, and allow the application to take place. Applying pesticides via mistigation could also reduce residue levels on berries because a fine mist of pesticide is emitted in a larger quantity of water.
Field trials have been conducted over the past couple of summers, and the results have looked very promising. According to residue analyses, pesticide residues on leaf and berry samples collected from fields treated with the mistigation method have been consistently lower compared with residues remaining on plant matter collected from fields treated with an air blast sprayer. Laboratory experiments testing mortality of flies placed on leaves collected from the mistigation field have been mostly similar to those collected from the air blast treated field. In addition, no SWD damage was observed in either of these fields, which is very reassuring.
This next summer we plan to continue our research by conducting additional trials using other pesticides with different chemistries, to see if they too work well being applied with the mistigation method.
Author: Heather Andrews