Feb 16, 2016
Multispecies mating disruption pursued in cranberries

Cranberry producers face a common dilemma when spraying their crops with insecticides: the prime time to spray to eliminate cranberry fruitworm is when the adult moths are in flight – during bloom. But that’s the same time honeybees are out doing their work.

A team of researchers led by the University of Wisconsin’s Shawn Steffan has come up with a solution. Don’t spray the moths – confuse them. That’s the basis of SPLAT, a pheromone-infused wax that male moths confuse with the scent of female moths ready to mate. What Steffan has discovered is that by the time the male moths figure out which scent is real, it’s too late.

“In essence, it’s moth birth control,” Steffan said.

This innovative approach to pest control has the potential to open additional markets for cranberry growers, particularly in Europe and Asia, which have stricter rules about pesticide residue levels. Organic growers are especially looking forward to getting their hands on this new pest control option.

Steffan and his team are working to mechanize the application of SPLAT. They are particularly excited about the potential of unmanned aerial vehicles (UAVs, better known as drones) and are working with Brian Luck, a University of Wisconsin biological engineering professor, to build a drone that can drop SPLAT.

Test drone flights that drop SPLAT on cranberry beds got under way this past fall, Steffan said.

SPLAT leaves the drone in the consistency of yogurt, and eventually hardens into a soft wax with the consistency of children’s modeling compound, Steffan said.

“We have a blueprint and materials,” Steffan said.

He and Luck are developing a prototype drone they can take to the field and test, he said. The testing, which will get under way after the cranberry harvest, will explore details such as how the SPLAT can be released from the drone and the height at which the drone needs to fly for optimum  coverage of the pheromone-infused wax.

Steffan’s plan is for drones to drop pheromone-infused product, which he refers to as SPLAT wax soup, onto the cranberry beds in dollops the size of Hershey’s Kisses. The dollops slowly release sex pheromones that smell like a female, and because the male moths cannot differentiate between the SPLAT and female moths, many of them will die before they find a real partner.

“You literally pre-empt the population from reproducing,” Steffan said. “Mating disruption (MD) is ideal as a way to keep males and females from finding each other. They need the pheromones to find one another, so if you can delay long enough, they eventually will die without mating.”

Using SPLAT to control moths instead of spraying insecticides on the cranberries has the potential to impact the bottom line of farmers, because they will save money on applications. Typically, farmers spray insecticides two to five times during the growing season, Steffan said.

Using SPLAT to control moths in cranberries also has environmental benefits, including saving pollinators such as honeybees from potentially damaging insecticides. A typical time to spray for cranberry fruit worm is when the adult moths are flying, which is the same time as cranberry bloom when the honeybees are out, Steffan noted.

“The approach is powerful and does not necessitate companion applications of insecticide,” Steffan said. “In U.S. apple and pear orchards, for example, the emergence of MD in the early ’90s allowed many growers to shelve most of their insecticides. Mating disruption has worked so well for the apple/pear industry of Washington that MD is now a mainstay of almost every orchard in the Pacific Northwest.”

Potential in cranberries

Mating disruption has been explored in cranberries, as well. Three separate approaches were tested in the mid- to late 1990s, all directed at black-headed fireworm, Steffan said.

In the earliest study, the fireworm pheromone was loaded into polyvinyl chloride carriers (PVC “ties”) and deployed in cranberry beds in British Columbia, Canada.

“This approach was successful at reducing mating frequencies and had adequate longevity, but the labor-intensive nature of coiling ties around cranberry uprights made this approach difficult,” he said.

Another pheromone dispensing system was subsequently investigated in Wisconsin cranberries. This system relied upon Metered Semiochemical Timed Release Systems (MSTRS), battery-powered devices that “puffed” pheromone plumes at periodic intervals, Steffan said.

“Unfortunately, this system suffered from low point-source densities in the field, ostensibly because each MSTRS device was expensive, so relatively few per acre could be installed,” he said.

The third dispensing system tested was a sprayable pheromone formulation by 3M Products.

“This material was sprayed over plant surfaces, obviously achieving countless point sources in the field; however, the trade-off in this case was that the material was spread so thin that the pheromone volatilized too quickly,” he said. “Of course, the most noteworthy aspect of past MD research is that in each instance, fireworm mating was effectively disrupted to some degree. This suggests MD has a place in cranberries, but the pheromone dispensing system needs to meet high standards for efficacy and commercial feasibility.”

The struggle to find an appropriate dispenser for pheromones in cranberries has been challenging, Steffan said.

“SPLAT should allow us to resolve the issue, striking a cost-effective balance between longevity and point-source density,” he said. “In a variety of systems (vineyards, pome and stone fruit orchards, blueberries, forest systems), SPLAT has effectively ‘shut down’ pheromone-baited traps, meaning that male moths could not find the traps in SPLAT-treated zones.

“Our primary goals in the current MD research program have been to demonstrate that a pheromone-based mating disruption program can reliably shut down mating and thereby reduce populations of the major insect pests of Wisconsin cranberries,” he said.

Over the last three years, Steffan said, they have accomplished the following: 1) created a multi-species blend using SPLAT as the carrier, 2) determined the longevity of SPLAT point-sources as a function of size and shape, 3) established ideal point-source spatial distributions and densities in the field, 4) deployed SPLAT at field rates over large acreage, and 5) achieved control of cranberry fruitworm and black-headed fireworm populations.

In 2014, SPLAT was applied at a rate of 1,000 point-sources per acre, Steffan said. A total of 50 acres was treated across five marshes (8-10 acre blocks at each marsh). A control block (conventional spraying regimen) was also monitored on-site.

“Our data showed that there was significantly less trap-catch for black-headed fireworm. In fact, there was a 95 percent reduction of trap-catch for fireworm. This suggests that moth mating was substantially reduced in the MD blocks. For cranberry fruitworm, there was a 75 percent reduction, which is good evidence of mating disruption, but clearly there is room for improvement.”

Steffan said it is important to note the number of infested berries in SPLAT-treated blocks was reduced 52 percent, “a significant reduction, and again evidence that fruitworm mating and reproduction was substantially reduced.”

“Altogether, this is evidence that MD can provide effective pest control for two of the major insect pests attacking Wisconsin cranberries,” Steffan said. “When used as a complement or replacement for insecticides, MD represents a sustainable, durable IPM tactic.

“Mating disruption programs will contribute toward the goal of reducing insecticide residues in U.S. cranberries, which should help to facilitate access to international markets.”

Ongoing work involves increasing pheromone loads in SPLAT and increasing the acreage treated, Steffan said.

“MD works best when applied over large areas, so it is important to scale up the deployment of SPLAT,” Steffan said.

Gary Pullano, associate editor





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