Lygus bug vacuums prove an effective organic tool

California Strawberry Commission researchers have designed and tested a double-barreled bug vacuum they say is more than twice as effective as standard models at sucking lygus bugs off the plants.

Many organic growers use bug vacuums as an effective method of controlling lygus bugs without insecticides, and conventional growers also use them to reduce the danger of insecticide resistance as part of an integrated pest management program.

"We brought a prototype into the field in October 2018 and removed two to three times as many lygus from the field as the grower standard," said Jack Wells, production automation engineer for the Strawberry Commission.

Lygus bugs are the most important insect pest in strawberries, as they disfigure the fruit badly by puncturing individual seeds, which stops development of the fruit in the nearby area.

Wells discussed the technical details of the new, improved version of the bug vac, and presented the results of trials, during the 2020 University of California Cooperative Extension Strawberry Production Research Meeting in Salinas.

The Strawberry Commission researchers had help from C&N Tractors in Watsonville as they built a three-bed version of their improved bug vacuum, which they said they tested with impressive results on a commercial strawberry field in Santa Maria.

Specifications for the new, improved bug vacuum are on the Strawberry Commission website (www.calstrawberry.com/en-us/Automation/Double-Barrel-Bug-Vaccuum).

This new, three-bed vacuum sucked an average of two to three times as many lygus bugs out of the Santa Maria field in seven side-by-side comparisons with the grower standard vacuum from October 2018 to October 2019.

In one of the trials, the Strawberry Commission model removed one-third of the lygus bugs in a single pass, whereas the grower's machine sucked out just 13% from a nearby strip of strawberries.

Driscoll's experimented with its first lygus bug vacuum more than 30 years ago, and since then growers and the Strawberry Commission have worked consistently to improve the effectiveness of the technology.

Many trials have been conducted to establish the optimum strength of the sucking, speed and height of the rig, in order to destroy the maximum number of lygus bugs with the minimum damage to the strawberry plants.

"The use of bug vacuums and research conducted on the optimization of these for lygus bug management have improved the efficiency of these machines from 2 to 3% to over 15% uptake," said Mark Edsall, Strawberry Commission field research manager, and Hillary Thomas from Naturipe Berry Growers in their Production Guideline for the bug vacuum.

"Optimization of these bug vacuums, including the addition of front plates, identification of the ideal ground and wind speed, has led to widespread adoption for lygus control, reducing insecticide applications industry-wide," they wrote.

The Production Guideline preceded the development of the newer machine with greater sucking power.

"Most vacuums operate at a hydraulic pressure of 2,000 pounds per square inch," Edsall and Thomas said. "Increasing the hydraulic pressure to 2,500 to 3,000 pounds per square inch by installing a high-pressure motor also improves the vacuum efficiency; this is observed especially in those vacuums that do not have a front plate. To achieve high hydraulic pressures, higher rated hydraulic hoses are required."

The recent design work by Edsall and Wells is the latest chapter in the attempts to improve the bug vacuum.

The newest bug vacuum generates 2,600 pounds per square inch of pump pressure and was tested on a tractor with 90 horsepower travelling across the field at 2 miles per hour.

"Our prototype has two fans," Wells said. "We tested the fan size, the number of fans and the clearance between the fans and the housing. After testing, we were able to optimize our motors and pumps."

There are significant obstacles to be overcome in even the best designed lygus bug vacuum program—including the upfront cost, because at least a tractor must be dedicated solely to the purpose of vacuuming bugs.

Researchers emphasized the importance of the skill and knowledge of the bug vacuum drivers.

"Operators should be trained on standard operating procedures and daily and seasonal maintenance activities," according to the Production Guideline. "Bug vacuums should be placed as close to the plant canopy as possible without causing damage to the crop. Vacuuming at canopy height picks up 60% more lygus bugs than when the vacuum is placed 6 inches above the canopy. The recommended driving speed for the bug vacuum is 2 miles per hour. No differences were found in efficiency when lower speeds were evaluated."

The weather and the time of day can make a significant difference in the effectiveness of the bug vacuum.

"Field trials showed that it is not necessary to wait after a disturbance event such as picking or vacuuming to perform another pass with a bug vacuum," according to Edsall and Thomas. "High efficiencies can be achieved in two consecutive passes. The time of the day affects the performance of the bug vacuums. More lygus is picked up in the afternoon. Canopy moisture is also an important factor affecting the efficacy of the vacuums. Efficiencies are higher when plants are dry."

(Bob Johnson is a reporter in Sacramento. He may be contacted at bjohn11135@gmail.com.)