Nov 26, 2014

Researchers study SWD pressure in cherries

Concern continues to mount about the potential impact of spotted wing drosophila (SWD) in tart cherries in Michigan.

Larry Gut, Michigan State University (MSU) Extension entomologist, has conducted trials at MSU’s Trevor Nichols Research Center on Montmorency single-tree plots to determine effective control methods.

“We know that in the cherry harvest in northwest Michigan, (SWD) was quite an issue this year. I know there’s a lot of concern,” Gut said.

The Trevor Nichols’ trials have been running for three years to look at the activity of insecticides against SWD in cherries.

“In cherries, we’re not trying to put together a management program at this point in time,” Gut said during a field day in October, which reviewed preliminary findings of various insect and disease research and efficacy trials carried out in the past season.

“The reason is SWD in the last four years has shown up in these cherries after harvest, right at harvest, in the middle of harvest. So, if you’re going to try and control them, you aren’t going to get a lot of efficacy data because there’s not a lot of treatment going on.

“So instead, the population really builds after harvest. We decided we’d run these (trials) through harvest, well past harvest and get some pressure against these materials and see how they stood up to SWD pressure,” Gut reported.

“I think this next year we probably need to start moving into some management programs, because SWD started showing up a little earlier and we’re actually seeing what we’re putting on to meet the preharvest intervals, and what we can do to actually control them and how long these materials last, but that’s not what this trial is all about.”

In addition to untreated trees, treatments included Imidan, Grandevo, Cyclaniliprole, Movento, Monterey bait and two levels of Exirel plus Monterey bait. The treatments were replicated four times with sprays timed for the first fly catch. Imidan was applied at a 14-day interval. All the other treatments were applied weekly. Fruit was harvested by limb shaking and was weighed in pounds.

“All these treatments were applied weekly, except for Imidan, and were applied first catch, early to mid-July, unlike the past few years,” Gut said. “For every treatment collected, the adult larvae in the cherries were reared out, so the data reflects actual SWD flies collected, and not just fruit flies in general.

“We have a really good place here to figure out the impact of SWD,” Gut said. “We had really good pressure here in our untreated, like 27 SWD per pound of fruit. That’s how the data is shown – actual adults reared from the fruit. There were really nice rate effects on all different treatments that were effective against SWD.”

“Imidan looks excellent,” he said. “Grandevo, this natural-like compound, looked good at a very high rate, then when we dropped the rate, it fell apart and doesn’t look like it’s as active against SWD.”

“Of the material in each of the trials, the diamide Cyclaniliprole looked very good,” Gut said. “Movento, in here for the second or third year, is showing good activity, which is sort of surprising us. We’ve run trials putting cherries under pressure from SWD and it looks good in other trials and this trial.”

Gut said one focus was to look at lower treatment rates in this trial.

“The last four treatments were with Exirel, with our without bait, using feeding bait, and Monterey bait,” he said. “Exirel, this diamide has good activity against various fruit flies and it looked very good in this trial.

“We looked at four ounces and eight ounces adding this Monterey rate in this trial, “ Gut said. “We got good control and it looked very promising, but data showed Monterey bait, without any insecticide, did as well as Imidan, and it did as well as Exirel and everything else. We have no explanation for this data.”

“We obviously need to repeat the trial,” he said. “We have a nice data set, with one anomaly.”

Pheromone research

Gut also addressed potential advances in pheromone mating disruption research. A series of trials has focused on attract-and-kill formulations for codling moth or other pests, rather than just using trapping mechanisms.

“There hasn’t been a way to draw them in and actually kill them,” he said. “We’ve seen that the toxicant and attractant must be separate.”

He said lab tests have sought ways to attract moths with an added element of using a toxicant that would kill them.

“Many formulations have operated via disruption, not insecticide poisoning,” Gut said.

He said development of a novel insecticide-treated fabric pouch that attracts and kills moths “appears promising.”

“If you separate the toxic from the lure by one centimeter, we got it to land on it,” he said. “It’s a way to force moths to touch it.

“Small plot trials on oriental fruit fly have looked good,” he said. “We’re working on leaf roller, which is one target of mating disruption that has been a bust. It’s a concept we came up with. It’s sort of a fun exercise and we’ll see where it goes.

“The key is to hang the bag vertically, so it’s not actually touching the lure and giving them a place to land where the lure isn’t there,” he said. “There needs to be a concentration away from the attractant. We’ll measure the catch in the traps to see if the population goes down and reduces fruit injury in these plots.”

– Gary Pullano