Published in Fruit Grower News. By Stephen Kloosterman Assistant Editor (11/17)

Michigan State University (MSU) continues to research new Weapons for the blueberry grower’s fight against spotted wing drosophila (SWD).

During a late September meeting, researchers and professors at the MSU Trevor Nichols Research Center (TNRC) in Fennville, Michigan offered a glimpse of trials of pesticides, organic methods and tighter spray timetables for controlling SWD.

The Asian vinegar fly, unlike a native species of vinegar fly, is able to lay its eggs in ripe fruit still on the vine and first was tracked in Michigan in 2010. The pest is a widespread challenge, reported by blueberry growers from Florida to British Columbia.

In Michigan, the pest took hold earlier than usual in 2017, adding at least one more generation in which to multiply its population.

“Very tough year,” said MSU professor and Extension specialist Rufus Isaacs, “Started early, went quickly.”

Pesticide trials
John Wise, professor of entomology, and research and Extension coordinator of TNRC, spoke about trials of different chemical treatments, including Cormoran, a dual mode insecticide from Adama that received EPA registration approval for the 2017 season on blueberries as well as pome, stone fruits and strawberries. Cormoran controls both the egg and larvae of pests with dual active ingredients of Novaluron and Acetamiprid.

Blueberries under a high pressure of SWD infestation were tested twice during the season – once on July 31 and again Aug. 14 – for SWD larvae levels per pound of fruit.

Ripe blueberries sprayed with a Cormoran alone at 20 fluid ounces tested “quite good” with SWD levels in the same ballpark as other pesticide programs in the trial. Cormoran wasn’t however in a group that Wise called “top performers.”

The top performers included:
• MustangMaxx sprayed at 4 fl oz/a
• A rotation of Imidan at 1.33 lbfa, and TriFol at 0.5 pt/100 gallons
• A rotation of Grandevo at 3 lb/a, R-56 at 0.13 percent v/v, Imidan at 1.33 lb/a, TriFol at 0.5 pt/100 gallons, MustangMaxx at 4 fl oz/a, Delegate at 6 oz/a and Exirel at 10 fl oz/a.

Other treatments of pesticides including Azera, Entrust, Vetatran and Harvanta also tracked competitively in the trials.

“All in all, I think the good thing is that were seeing an increased selection of tools compared to, let’s say, two years ago, where we would have said, ‘spinosyns, OP’s (organophosphates),
pyrethroids – that’s all we’ve got.” Wise said.

Tighter timing, curative control

Isaacs spoke about trials to test if tighter timing for spray schedules and the added mix of neonicotinoids could improve control of SWD.

Some growers harvesting blueberries later in the season have encountered high SWD pressure, and some have had success shortening their intervals between re-application.

“It’s not necessarily saying that you have to be spraying at every four days all the way through the season, but at these points where were seeing the population increase, and it’s really challenging to keep ahead of it, these data suggest that our frequency is really important” Isaacs said.

While the first technique seemed to have originated with growers; the other came from researchers. Isaacs said that in research, neonicotinoids have shown some ability to cure SWD eggs and larvae already in ripe blueberries. Control before infestation, of course, is preferable, but preventing larvae from growing limits population growth.

In the trials, some rotating broadspectrumpesticides were mixed with neonicotinoids, and applied with varying intervals. Ripe berries were collected Weekly from the interior of the bush and tested for SWD infestation. Preliminary results distributed at the field day seemed to show shortened intervals with neonicotinoids had the lowest average number of SWD per ounce of berries.

The trick, though, is finding time to harvest the berries in between sprays – in trials, the berries were not harvested in order to keep the SWD pressure high and test the effectiveness of the sprays.

Organic methods
Isaacs’ post-doctorate research assistant Philip Fanning spoke about another trial of non-chemical, or organic, methods for making the bushes in a particular block less hospitable to SWD population.

Placing a type of woven black synthetic fabric on mounded-up row of dirt at the base of the bushes increased heat in the bushes, making them less hospitable on hot days, and the plastic grew hot enough to cook the pupae that fell on it. A traditional wood chip mulch provides hospitable environment for the pupae.

In trials this year, the SWD infestation came two weeks later than other blueberry farms in the area.

Another technique discussed was opening up the canopy of the bushes – an approach that’s already showing positive results in North Carolina.

“If you can open up this canopy, you can reduce humidity and reduce hospitability for spotted Wing drosophila,” Fanning said. FGN