Controlling grape root borer with pheromones

Controlling grape root borer with pheromones

Summary

The grape root borer is an insect pest native to the Eastern U.S. The larval stage of the moth can do significant damage, living at least two years and possibly longer in the soil feeding on grape roots. They can destroy and kill mature grape vines. The most widely used control method involves using a restricted-use organophosphate pesticide, which is expensive and time consuming. Recently a new pheromone system has become available for use in grape root borer mating disruption. This system utilizes the pheromone mix of the European leopard moth, which differs from the pheromone mix in the standard grape root borer pheromone lure. Each of the new pheromone dispensers contains 80 times more pheromone than the standard grape root borer pheromone lure currently available. The new dispensers are labeled to be placed in the vineyard at a concentration that releases 300 times more pheromones than the standard grape root borer pheromone lures used in our previous NESARE projects. The effectiveness of the new pheromone system has been deemed successful by the inability to trap male grape root borers in a vineyard. The inability to trap male insects is known as trap shutdown. Utilizing trap shutdown as an indicator of mating disruption success is questionable.

Grape root borer populations in our vineyard never decreased utilizing the standard pheromone lures in previous projects, although the numbers did not increase. The aim of the multi-year project will be to test the new system at different rates and its effectiveness in reducing or eliminating grape root borers in our vineyard. The new pheromone system will be utilized for two years. In the third year only traditional pheromone traps will be placed in the vineyard to determine if the new pheromone system has been successful in reducing the grape root borer population.

Objectives/Performance Targets

In the summer of 2015 testing on the effectiveness of Isomate GRB pheromone dispensers was continued. The vineyard test area was divided into 9 blocks with 3 plots each. On June 19, a standard bucket trap with a grape root borer pheromone lure was placed at the center of each plot. The traps monitor the effectiveness of the Isomate GRB dispensers. Isomate GRB dispensers were placed in the vineyard on June 20 in a new randomized complete block design that differed from the previous year. The same numbers of Isomate GRB dispensers that were utilized at the end of the testing in 2014 were repeated initially in 2015. Nine plots received a density of approximately 50 dispensers per acre, while dispensers were placed in nine other plots at a rate of 75 per acre. The last nine plots had a dispenser density of 100 per acre, the recommended amount. A male grape root borer was first observed in the vineyard on July 8.

On July 13, one male grape root borer was caught in a plot with 5 Isomate dispensers or a density of approximately 50 per acre. The average over the entire test area was approximately 75 dispensers per acre. With the capture of a grape root borer, the density of Isomate dispensers was increased to 100 per acre or 9 per plot for the entire test area. Every plot now contained nine dispensers. This density is the amount recommended on the label.

Another male grape root borer was captured on July 21 in a pheromone trap. The density of Isomate dispensers was not increased because the recommended level had been reached. No additional male grape root borers were captured in the traps for the rest of the season. Even with the recommended number of Isomate dispensers per acre, total trap shutdown was not achieved.

Pheromone traps were again placed outside of the vineyard to determine if Isomate dispensers would influence the area outside of the vineyard. Traps were placed at 200 foot intervals up to 1000 feet from the vineyard. The traps were situated in four directions from the vineyard; north, east, south and west. The traps with pheromone lures were placed on July 1. The first moths were captured in these traps on July 11. The Isomate dispensers appeared to have some effect on the surrounding area, but not as significant as in 2014. Over the entire season a total of 8 moths were captured 200 feet from the vineyard, 6 moths at 400 feet, 2 moths at 600 feet, 5 moths at 800 feet and 13 moths at 1000 feet. More moths were captured this year close to the vineyard as compared to the previous year.

A total of 16 Isomate dispensers were placed at other location, miles from the vineyard, to measure the loss of pheromones over time that are emitted from the dispensers. The study was initiated on June 28 and the dispensers were weighed weekly until August 30. Over this time period each dispenser lost about 0.002 grams of pheromone per week, the same result as in 2014.

Accomplishments/Milestones

The Isomate grape root borer dispensers definitely caused a substantial decrease in the capture of male grape root borers in the pheromone traps. The same results occurred in 2014. In most years at least 300 male grape root borers are captured in our vineyard. Isomate dispensers do cause substantial trap shutdown, but a male grape root borer was caught at the recommended dose of 100 dispensers per acre.

Does trap shutdown mean males cannot find females? Is grape root borer mating still occurring? A mating pair of grape root borers was observed on July 21 just 112 inches from an Isomate dispenser. A similar result occurred in 2014. This observation would indicate that mating is still occurring in close proximity to Isomate grape root borer dispensers.

A field day detailing the progress of the project was held at the vineyard on August 20.

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