Cutworms come out at night to feed on grape buds.

Cutworms come out at night to feed on grape buds.

Pyrethroid barrier trunk sprays have proven effective against cutworms in Washington State, but for growers who want to avoid using pyrethroids, an organic alternative is looking pretty "hot" in research trials.

The industrywide adoption of trunk barrier sprays for cutworms has greatly helped reduce the use of pesticides by Washington grape growers, said Dr. Doug Walsh, Washington State University entomologist and integrated pest management coordinator. Using pyrethroid insecticides like Capture (bifenthrin) and Danitol (fenpropathrin) have allowed grape growers to move almost completely away from broad-spectrum chemicals Lorsban (chlorpyrifos) and dimethoate that were traditionally used for cutworm control but interfered with IPM.

In response to third-party certification programs in Europe that are "down on pyrethroids," Walsh has been investigating alternatives for cutworm barrier sprays. "I’ve looked at an extensive list of materials to replace pyrethroids to see if we can find different ways to provide control," he said during the Washington State Grape Society meeting last November.

He is experimenting with several plant oils and extracts, including capsaicin, which is a component of chile peppers, as well as garlic powder, and peppermint, neem, and cinnamon oils. Application methods have varied from applying the mixtures as a blanket cover spray, barrier spray, and paint, to a snap-on bracelet around the grapevine trunk. In his latest trials, he mixed the hot pepper wax with a food-grade grease and applied it as a paint to the trunks.

Cutworm pressure in his trials was low in 2008, he reports, noting that with the pyrethroid barrier sprays, they only had two cutworm strikes per 15 vines, which marked a successful treatment. In the same trial, the hot pepper wax as a spray didn’t work as well, but when painted on, it showed significantly better results than the nontreated control.

He also studied the efficacy of generic pyrethroid materials—a cheaper option to the pyrethroids still under patent—and found good control.

"Are we there yet with alternative controls?" he asked. "We know that any of the pyrethroids work well. We also found out that hot pepper wax mixed with food-grade grease and garlic powder both worked well."

However, he did learn that several products, such as the cinnamon and peppermint oils, worked the opposite and actually increased the number of cutworm strikes. "They might be flavor enhancers," he said.

Walsh plans to continue testing the hot pepper and garlic powder materials in 2009 and will test a wick applicator used in cereal grain production to apply herbicides to the broadleaf weeds that are taller than the cereal grasses. He believes the wick applicator could be an effective way to apply the "gloppity-gloo" pepper and grease treatments. Hot pepper wax, a registered pesticide, is approved for organic use and is commercially available. Garlic powder is not registered.

WSU’s Dr. Francis Pierce, director of the Center for Agricultural Precision Systems, is working with Walsh to develop an autonomous spray unit that could perform multiple tasks in the vineyard at the same time, applying trunk barrier sprays or glop as well as other tasks, like sucker management.

Attract and kill

For those who want to get away from barrier sprays, Walsh has been experimenting with the "attract-and-kill" method of killing flying, adult cutworm moths. He’s had success in significantly reducing the number of moth flights in vineyards when an attractant is mixed with a pyrethroid or the neonicotinyl Assail (acetamiprid). Inexpensive bait stations that cost about 60 cents per station can be made from compact discs or small pieces of PVC (polyvinyl chloride) pipe, smearing the moth attractant and insecticidal killing agent on the CD or inside the PVC pipe and hanging it in the vineyard.

Research conducted with the CDs hung in a vineyard in 2003 showed that the method was effective in reducing moth flights if the area was blanketed with the bait-and-kill stations. Tests showed that both 50 CDs and 10 CDs per acre were effective in shutting down moth flights.

While the data show that the bait-and-kill concept works in reducing the number of adult moths, he’s not sure that translates into easier cutworm control the following year. "The problem has been that we have never been able to really prove in the subsequent fall that we really reduced the cutworm numbers. We don’t have a way to prove that we are doing any good."

Walsh hopes to learn something from moth research currently being conducted in hops and poplars that might relate to grapes and cutworms.