Apr 30, 2015
Using exclusion netting helps manage SWD in blueberries

Dale-Ila Riggs, owner of The Berry Patch at Stone Wall Hill Farm, a diversified fruit and vegetable farm in Stephentown, New York, has been attempting everything imaginable to reduce the impact of spotted wing drosophila in blueberries.

Riggs estimates SWD damage cost her operation $8,000 in lost blueberry income alone.

“Two years ago, we lost 40 percent of our crop to SWD,” she said.

Riggs harvests all of her fruit crops for fresh, direct-market sale from the farmstead, at farmers’ markets and to dozens of regional restaurants.

“We need a system that will control SWD yet be practical for working around the berries and less costly,” she told an audience at the 2015 Mid-Atlantic Fruit & Vegetable Conference in Hershey, Pennsylvania.

Riggs recently started “Berry Protection Solutions” as a distributor of Tek-Knit insect netting and other agricultural fabrics. She also is the president of the New York State Berry Growers Association and has led the charge to obtain funding for research solutions for managing SWD, obtaining $1.3 million dollars in the last three years for SWD research and education programs.

“I think (netting) is a technology that holds great promise for growers that don’t want to spray to combat SWD,” Riggs said.

Riggs earned her master’s degree in horticulture and adult education from Oregon State University. A fifth-generation Vermonter, she and her husband, Don Miles, started their now 240-acre farm from scratch in 1997. Prior to starting her farm, she was a regional vegetable specialist for Cornell Cooperative Extension, winning the National Crop Production Award in 1997.

“I received a Northeast Sustainable Agriculture Research and Education (NE SARE) Farmer grant to test the feasibility of using insect netting to prevent SWD from infesting my half-acre blueberry planting,” she said.

Because the NE SARE grant did not cover the costs of the netting, funding from the New York state legislative allocation to the New York State Berry Growers Association was used to purchase the netting from Tek-Knit Industries in Quebec, Canada.

“I adapted my existing bird netting support system of greenhouse hoops to work as a support system for the netting,” she said. “Six rows of blueberries (250 feet long) were covered with 80-gram netting using three pieces of 26-foot wide netting. The pieces of netting were joined together by wrapping them around greenhouse purlins and clamping them, using plastic greenhouse clamps approximately every two to three feet.

Riggs said the sides were anchored on the ground by wrapping them around purlins, clamping the netting and placing rock bags on the netting approximately every five feet. One row of blueberries was covered with one piece of 26-foot wide 60-gram netting from Tek-Knit, and one row was covered with only bird netting.”

The row that was covered with bird netting was sprayed with two applications of Delegate plus sugar on July 29 and Aug. 5, and two applications of Assail plus sugar on Aug. 10 and Aug. 24.

Berries were harvested for sale from July 11 through Sept. 20, she said. Berries were sampled weekly from July 15 through Sept. 15, examined through a dissecting scope for oviposition damage and put in a rearing chamber to rear out SWD.

The control plot and 60-gram netting had 75 berries collected every week; the 80- gram netting had 225 berries collected every week.

“Despite the prototype nature of the project, and learning curves associated with anchoring netting that survived through 60 miles per hour winds and hail in thunderstorms, this trial clearly shows that 80 gram insect netting is a viable alternative for managing SWD,” Riggs said. “Beside providing protection from SWD, it prevents bird predation, and protects the crop from hail.”

Berries sampled on Sept. 8 had a total of eight SWD reared out from a sample of 225 berries. Berries sampled on Sept. 15 had a total of four SWD emerge from 225 berries. The first SWD emerged from fruit collected on Aug.14 – one each in the 60-gram and control treatments.

Peak infestation occurred in the 60-gram netting on Sept. 2 (never sprayed), when 47 SWD emerged from 75 berries. Peak infestation occurred in the control on Sept. 8 (last spray was on Aug. 24), when 51 SWD emerged from 75 berries.

At The Berry Patch, the first SWD larva was found in raspberries on July 22.

Riggs plans some tweaks in the netting system for 2015.

“Because the wiggle wire attachment system worked so well to attach the netting on our vestibule last year, I am going to use it on the main planting this year as well,” she said. “I will use a continuous purlin the length of the planting (like we did last year) but I will add wire lock channel to the top and attach the netting to it with wiggle wire.

“I am also going to put inexpensive 1 x 6’s around the perimeter of the planting with wire lock channel and attach the netting at the ground level to the baseboard,” she said. “This will allow me to use the full width of the netting more efficiently, use less greenhouse hoops for structural supports, and prevent the possibility of abrasion on the netting from where we attached the clamps.”

Riggs was one of two growers in eastern New York who received NE SARE farmer grants to look into exclusion netting. Lawrie Nickerson, Hay Berry Farm, was the other recipient.

The material used by Riggs, an 80-gram netting manufactured by Tel-Knit Industries, was shown in the lab to exclude SWD adults. The purpose of the trials was to examine and perfect the system and to ensure that the netting did not cause any damage to the berries in terms of plant growth and/or yield.

In the first trial, each row of plants were covered, which resulted in “excellent insect control with no effect on berry quality or overall yield.”

In the second trial, the entire planting was covered and it was determined that the 80-gram net performed much better than the 60-gram material, which excluded SWD only a week more than the control.

The cost of covering an acre of blueberry planting with insect netting would likely approach $10,000/acre, depending on the support system used. The life of the net is seven years, so the amortized cost per year is $1,428, not including labor.

Riggs tested the netting on a half-acre of blueberries that ripen over a two-month period. The vigorous plants were 8 feet tall and 8 feet wide. She’s evaluated two mesh sizes of netting. The major portion of her planting is covered with the very fine netting. One row is covered with a less-fine netting that’s also less expensive.

A similar SARE grant helped Hay Berry Farm, an organic, u-pick berry and herb farm in Hoosick Falls, New York, control SWD. Owner Lawrie Nickerson had originally planned to plant 4.5 acres of blueberries, but stopped at 3 acres after the 2012 planting because of SWD. In 2013, netting effectively excluded SWD and other insects of similar size and larger from the trial area.

“The upshot is that insects the size of fruit flies could not get past the netting. Using the netting didn’t negatively affect our harvest weight, yield, or timing,” Nickerson said. “In some cases, the berry yield was slightly higher.”

“Netting could be an excellent strategy for coping with SWD, particularly as an alternative for organic growers,” said Cornell Cooperative Extension fruit and berry specialist Laura McDermott.

Nickerson and Riggs tried numerous measures, including insect trapping and weed mats, as part of their grant projects.

Gary Pullano

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