Final report for FNE14-804

Controlling grape root borer with pheromones

Project Type: Farmer
Funds awarded in 2014: $14,802.00
Projected End Date: 10/31/2017
Grant Recipient: Landey Vineyards
Region: Northeast
State: Pennsylvania
Project Leader:
R. Martin Keen
Landey Vineyards
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Project Information

Summary:

The project was initiated to test the effectiveness of Isomate GRB in controlling grape root borer in an older producing vineyard. Like many pheromone studies, this experiment gave inconclusive results. Our vineyard was divided into 27 plots using a randomized complete block design. There were 9 replicates of three different treatment levels of Isomate GRB, which contains high levels of pheromones that are meant to disrupt the mating ability of grape root borers. Pheromone traps were placed in and outside of the vineyard to monitor the number of male grape root borers. The depletion of pheromones from Isomate GRB twist ties was also measured. Trap shutdown or the absence of capturing grape root borers in pheromone traps within the vineyard did occur at all treatment levels during the two years of treatments. Low levels of grape root borers were captured in the traps placed outside of the vineyard. The amount of pheromones in Isomate GRB is sufficient to last the entire season. Statistical analysis of the results in the third year was mixed. The number of grape root borers captured was reduced from previous years and with one data set the results were statistically significant, but with another they were not. Mating was observed in the vineyard each year the Isomate GRB was present. In each of the three years of the project a field day was held at our vineyard and a presentation was given at the 2017 Mid-Atlantic Fruit and Vegetable Convention in Hershey, Pennsylvania. Approximately 100 people were in attendance. A website www.graperootborer.com has been developed to make the results available to anyone interested in the NE-SARE project.

Introduction:

The grape root borer, Vitacea polistiformis (Harris), is an insect pest native to the Eastern U. S. At the present time it has not been reported anywhere else in the world. The larvae of this clear winged moth feed on the mature roots of all grape species and hybrids. An infestation of grape root borer is not immediately apparent. It takes years for the borer to reach a population level that causes economic damage. Once the number of larvae reach a sufficient level the damage is striking. Within four years the production of one cultivar in our vineyard was reduced 70%. This level of damage occurred twenty years after the vines were initially planted.

Currently many vineyard owners are unaware of the serious problems that can result from grape root borer. Many new plantings of grape vines have occurred in southeastern Pennsylvania and other areas of the eastern U.S. in the last twenty five years. Damaging levels of grape root borer might only now be apparent. Unfortunately one of the main control methods is the use of Lorsban (chlorpyrifos), an organophosphate. The use of Lorsban-4E, a restricted use pesticide, is time consuming. A half gallon of the diluted spray mixture is sprayed on a 15 square foot area around the base of each vine. Previously it was thought the spray treatment must be used at least two years in a row because the larvae stage lasted for only two years. Current research would indicate the larval stage can last for at least three years and possibly longer, requiring more treatments with Lorsban (personal communication, Dr. Roger Williams, Ohio State University, June 18, 2005 and e-mail communication, Dr. John Meyer, North Carolina State University, December 1, 2005) or any other treatment method.

The female grape root borer moth uses a scent (pheromone) to attract males. This was first reported in 1918.1 The major chemical component (E,Z-2,13-octadecadien-1-ol acetate or EZ) of the pheromone was identified in 1983.2 A secondary compound (Z,Z-3,13-octadecadien-1-ol acetate or ZZ) was found to improve the capture rate of male moths by 7 times in 1987, but the compound has not been identified in the female pheromone.3 The blend of pheromones used commercially today is a 99:1 ratio of EZ:ZZ. A rubber septum lure impregnated with the grape root borer pheromone is currently available to the commercial grape grower. Each rubber septum lure contains 1 milligram of EZ:ZZ pheromone blend. These rubber septa lures are used in various types of traps to capture male moths.

One goal of this project is to test the effectiveness of a different control method. A new pheromone system, Isomate GRB, has recently been introduced for the control of grape root borer, but the pheromone mix is that of another moth species, not the grape root borer. All previous published testing with this pheromone mixture has been with a product known as Isonet Z, not Isomate GRB. The concentration of the pheromone mixture in Isomate GRB is 15% greater than that found in Isonet Z. One report on the use of this new pheromone mix for the control of grape root borer has been published and the research was done in Florida.4 The new pheromone system was tested for two years, but no testing was done in the third year to determine if the grape root borer population had actually decreased. The study used trap shutdown, the absence of capturing male moths, as an indicator of success, but noted that “trap shutdown alone does not prove that mating disruption has occurred.” The minimum number of pheromone twist ties per acre required to control grape root borer has not been established and neither has the rate at which the new pheromone mix is depleted in the vineyard.

I am a part-time farmer currently farming 5 acres with my brother and sister. The total size of the present farm is only 7.8 acres. My brother and I first planted wine grapes on the farm in 1974. Today a total of 3.4 acres is planted in wine grapes and includes the French hybrids: seyval, vidal and chambourcin and a European vinifera, pinot noir. The vidal was planted in 1976, chambourcin in 1980, seyval in 1984 and 1986 and pinot noir in 2007, 2008 and 2009. Vines are grown with unilateral or bilateral cordon training on the bottom wire. A standard three wire system with wires at 36, 54, and 72 inches is used as the trellis system for the French hybrids. A seven wire trellis system with movable catch wires is used for the pinot noir. The vines are trained using vertical shoot positioning. Vineyard spacing is 9 foot wide rows with 6 feet between the vines in the row. An area of approximately one half acre is used for the growing and production of grafted vines and other varieties. The grapes are sold wholesale to wineries and home winemakers in Pennsylvania and Maryland. From 1989 until 2004 I also grew one half acre of saffron on the farm.

The farm is composed entirely of Duffield silt loam with a 0 to 3% slope on the top of a small hill. The location provides excellent air drainage with no frost pockets. The surrounding area is almost entirely in farmland and is located in an agricultural security area. There have been no changes in the operation since the initiation of the SARE project.

The initial technical advisor for this project was Mark Chien of Pennsylvania State University . Since 1999, Mark had been the wine grape agent for Penn State Cooperative Extension, serving all of Pennsylvania. Mark left Penn State in 2014 and took a position with Oregon State University.

Timothy Elkner of Penn State Extension has served as the technical advisor for the remainder of the project. He is an extension educator for a three county area with expertise in commercial small fruit production.

1Brooks, F. E. 1918. Papers on deciduous fruit insects: II. The grape root borer. U.S. Dept. of Agric. Bull. 730:1-28.

2Schwarz, M., J. A. Klun, B. A. Leonhardt, and D. T. Johnson. 1983. (E,Z)-2,13 octadecadien-1-ol acetate. A new pheromone structure for sesiid moths. Tetrahedron Letters 24: 1007-10.

3Snow, J. W., M. Schwarz, and J. A. Klun. 1987. The attraction of the grape root borer, Vitacea polistiformis (Harris) (Lepidoptera: Sesiidae) to (E,Z)-2,13 octadecadienyl acetate and the effects of related isomers on attraction. J. Entomol. Sci. 22(4): 371-374.

4Weihman, S. W., and O.E. Liburd. 2006. Mating disruption and attract-and-kill as reduced-risk strategies for control of grape root borer Vitacea polistiformis (Lepidopter: Sesiidae) in Florida vineyards. Fla. Entomol. 89(2): 245-250.

Project Objectives:

This experiment was initiated to test the effectiveness of Isomate GRB in our vineyard. The goals of this experiment were fourfold.

  • First, determine if Isomate GRB is effective in mating disruption.

  • Second, attempt to ascertain if lower numbers of twist ties than the labeled amount will achieve mating disruption.

  • Third, calculate the rate of pheromone loss from Isomate GRB twist ties.

  • Finally, does the effectiveness of Isomate GRB extend beyond the test area.

Cooperators

Click linked name(s) to expand
  • Timothy Elkner - Technical Advisor

Research

Materials and methods:

Several factors made our vineyard a good choice for testing. The vineyard is almost entirely surrounded by farmland. The closest vineyard of any size is just over 5 miles away. The closest wild grapevine is over 1000 feet from the vineyard and the closest woodland that could support more wild grapevines is over a 1/3 of a mile away. There are residences at either end of the vineyard. Monitoring of grape root borer populations with the same system has occurred since 2003, giving an unprecedented record of population levels. Almost the entire vineyard has been divided into a randomized complete block design since 2003 for grape root borer testing and experimentation.

For this study, as in previous work, the vineyard was divided into 9 blocks of 11664 square feet each, measuring 72 feet by 162 feet. Each block is subdivided into 3 plots. Each plot is 3888 square feet, measuring 54 feet by 72 feet. With a total of 27 plots, there were 9 replicates of three different treatment levels of Isomate GRB. The different treatment levels were utilized to test if lower densities of Isomate GRB would achieve the desired trap shutdown. Treatment levels for the plots were randomly selected using a ten thousand random digit table. A universal standard moth trap with one EZ:ZZ pheromone lure was placed in the center of each plot at a height of approximately 65 inches above the ground. The standard moth trap is a bucket type trap with a green top, yellow midsection and a white bucket.

In 2014 and 2015, universal standard pheromone traps with one EZ:ZZ lure were also placed outside of the vineyard to see if trap shutdown extended beyond the vineyard and to check if male grape root borer moths from the vineyard could be attracted to traps placed outside of the treatment area. Traps were placed at 200, 400, 600, 800 and 1000 feet beyond the edge of the vineyard in four directions to account for changes in wind direction. The directions were close to due north, east, south and west. Traps placed to north were along a tree line between fields of alfalfa, corn and/or soybeans. To the east and west, the traps were along a road and placed in fields of corn or Sudan grass. Traps placed to the south were placed along a grass waterway in a field of corn. All the standard traps with an EZ:ZZ lure were suspended from iron rods at a height of approximately 58 inches above the ground.

The pheromones in Isomate GRB are based on those secreted by the female European leopard moth (Zeuzera pyrina L.) and currant clearwing (Synanthedon tipuliformis Clerck), not the grape root borer. Active ingredients are E,Z-2,13-octadecadien-1-ol acetate or EZ and E,Z-3,13-octadecadien-1-ol acetate or EZ-3 in a ratio of 95:5. The major pheromone for the grape root borer, currant clearwing and European leopard moth is the same but the secondary compound is different. The twist ties are made by the Shin-Etsu Company of Japan and each twist tie dispenser contains 80.43 milligrams of pheromones. High concentrations of Isomate GRB pheromones are meant to confuse the male grape root borers. For grapes the labeled amount is 100 dispensers per acre and the dispensers are to be placed on the lower training wire or mid-canopy in a uniform pattern across the vineyard. In this study the dispensers were placed on the middle wire at approximately 54 inches above the ground.

The loss of the pheromone mixture from Isomate GRB twist tie dispensers was recorded in 2014 and 2015 at a site 8.5 miles from the vineyard. Each year a total of 16 dispensers were placed outside in conditions similar to those in the vineyard. Four sets of four ties each were weighed weekly to determine the rate and amount of pheromone loss.

All statistical analysis was done utilizing procedures found at vassarstats.net.

Research results and discussion:

The results on the effectiveness of Isomate GRB in causing mating disruption were mixed. With one data set the results were statistically significant, while with a different data set it was not. Also it was not possible to determine if lower numbers of Isomate GRB twist ties could achieve mating disruption due to the volatile characteristics of the pheromone mixture. The rate of pheromone loss from the Isomate GRB twist ties was determined and the twist ties were found to have a sufficient quantity to last the season. The effectiveness of the Isomate GRB twist ties did not extend beyond the test area.

Results from within the vineyard

2014

Standard moth traps were placed in the vineyard on June 19, 2014. Twist ties were placed in the vineyard on July 1, 2014. No moths had been captured in the traps to this point, but one male moth had been seen around a trap on June 30th. Isomate GRB twist ties were placed in the vineyard at three different concentrations. The initial concentrations of Isomate GRB were nine plots with no twist ties, nine plots with 2 twist ties each, equal to 22 per acre, and nine plots with 5 twist ties, equal to 56 per acre. The average number of twist ties in the test area was 26 per acre. On July 12, 2014 a male moth was captured in one of the plots with no twist ties. The concentration of the twist ties was increased the same day to an average of 52 per acre in the test area. There were now nine plots with no twist ties, nine plots with 5 twist ties each, equal to 56 per acre, and nine plots with 9 twist ties, equal to 101 per acre, the recommended amount.

Again a male moth was captured in a plot with no twist ties on July 18th. Twist ties were now added to the plots that previously had no twist ties. The number of twist ties was increased the same day to an average of 78 per acre in the test area. There were now nine plots with 5 twist ties each, equal to 56 per acre, nine plots with 7 twist ties each, equal to 78 per acre, and nine plots with 9 twist ties, equal to 101 per acre. No male moths were captured in a trap for the rest of the season, but a mating pair was observed on July 26th at 4:10 PM in a low density (56/acre) plot 14.5 feet from an Isomate GRB twist tie.

2015

In 2015, standard moths traps with an EZ:ZZ lure were placed in the center of each plot on June 19th. The following day, Isomate GRB twist ties were placed in the vineyard at the same concentrations that were in place at the end of testing in 2014 for an average of 78 twist ties per acre in the test area. Each plot’s concentration was randomly reselected using a ten thousand random digit table. Nine plots contained 5 twist ties each, equal to 56 per acre, nine plots contained 7 twist ties each, equal to 78 per acre, and nine plots contained 9 twist ties, equal to 101 per acre. On July 13th, a male moth was captured in a plot with 5 twist ties. The same day the concentration of Isomate GRB dispensers was increased to 9 twist ties per plot for the entire test area. The concentration of twist ties was now at the recommended level of 100 per acre. A mating pair of grape root borers was observed on July 21st at 4:40 PM just 9.3 feet from an Isomate GRB twist tie and a male moth was also captured in a pheromone trap the same day. Although the Isomate GRB was now at the recommended level of 100 ties per acre throughout the entire test area, mating was still occurring and one male grape root borer was captured in a pheromone trap.

2016

In 2016, no Isomate GRB twist ties were placed in the vineyard. Standard moths traps with an EZ:ZZ lure were placed in the center of each plot on June 24th. On July 5, the first male grape root bores were captured, four in number. The greatest number of root borers were counted on July 18th with a total of 97. The last two were captured on August 12. A total of 313 male grape root borers were captured in the vineyard during 2016.

Statistical analysis of the results varied. If the total grape root borers captured in 2016 is compared to the totals captured from 2009 to 2013, when 27 traps were also used, the number captured in 2016 is significantly different at a 5% level using a two tailed single sample t test. When the results from 2016 are compared to the total captures for 2003 to 2013, no significant difference was found using a two tailed single sample t test.

Isomate GRB range outside of vineyard

2014

In 2014 male grape root borers were captured in the pheromone traps placed outside of the vineyard. At 200 feet, 3 were captured, at 400 feet-3, at 600 feet-4, at 800 feet-3 and at 1000 feet, 12 were captured. The low numbers captured at 200 to 800 feet are most likely moths in the general area of the traps and would indicate that moths were not leaving the vineyard. It would also indicate that trap shutdown does not extend beyond the vineyard. A Tukey’s HSD test on the trap captures based on distance from the vineyard showed the number captured at 1000 feet was significantly greater than all the other distances at a 5% level. There was no statistical significance based on the direction using a one-way ANOVA.

2015

Male grape root borers were again captured in the pheromone traps placed outside of the vineyard in 2015. At 200 feet, 8 were captured, at 400 feet-6, at 600 feet-2, at 800 feet-5 and at 1000 feet, 13 were captured. More grape root borers were captured at 200 feet than in 2014, but the numbers were still fairly low based on the hundreds that were previously captured in the vineyard. Again this would indicate that moths were not leaving the vineyard and trap shutdown did not extend beyond the vineyard. No statistical significance was found in 2015 in either the distance from the vineyard or the direction of the traps using a one-way ANOVA.

Pheromone Loss

2014

The loss of the pheromone mixture from Isomate GRB twist ties was recorded in 2014 and 2015 at a site 8.5 miles from the vineyard. A total of 16 twist ties were tested. Four sets of four ties each were weighed weekly. Each twist tie contains 80.43 milligrams of the European leopard moth pheromone mixture. In 2014, over the course of 73 days, each twist tie lost on average 20 milligrams or 25% of the Isomate GRB pheromones. The daily loss was approximately 0.274 milligrams per day per twist tie. During the 73 day testing period, the average daily high temperature was 80.5°F. The highest temperatures were 4 days of 90°F.

2015

The same results were recorded in 2015. In 2015, over the course of 63 days, each twist tie lost on average 16 milligrams or 20% of the Isomate GRB pheromones. The daily loss was approximately 0.254 milligrams per day per twist tie. During the 63 day testing period, the average daily high temperature was 82.7°F. The highest temperatures were 3 days of 91°F and 2 days of 90°F. Although the average high temperature was greater in 2015, the loss of pheromones was basically at the same rate as in 2014. In our region the Isomate GRB twist ties would definitely have sufficient pheromones to last the entire season of grape root borer activity.

These results compare favorably with testing done in 1987 on the Shin-Etzu twist tie dispensers in Arkansas. In these tests, twist ties with 40 milligrams of EZ lost 0.23 milligrams per day and twist ties with 40 milligrams of ZZ lost 0.19 milligrams per day.1

1Johnson, Donn T., Barbara A. Lewis, and J. Wendell Snow. 1991. Control of grape root borer (Lepidoptera: Sesiidae) by mating disruption with two synthetic sex pheromone compounds. Environ. Entomol. 20(3): 930-934.

Research conclusions:

In general the proper testing of pheromone based products is very difficult and creates its own special problems. First of all, pheromones are volatile and do not remain in the test area. Airflow can carry pheromones unknown distances that might have an effect on the target insects in the area. It is unknown from what distance an EZ:ZZ pheromone lure can attract a male grape root borer.

Populations of grape root borer vary naturally from year to year due to unknown environmental factors that are not quantified. In our own vineyard, populations varied with no treatment applied. In the four years of 2003 through 2006, the average number of male grape root borers captured was 219. During the four years of 2008 through 2011, the average was 466. Was the increase solely due to rising population levels or was another factor also present? In the two years following 2011, the average number captured decreased to 359. This is a substantial decrease and there is no known reason for it to occur.

In this study, the number of Isomate GRB twist ties required for mating disruption could not be determined. This was due to the volatility and movement of the pheromones between plots. Trap shutdown did occur at a much lower number of twist ties than the labeled 100 per acre. Even at 25 twist ties per acre trap shutdown was occurring, but trap shutdown does not mean mating disruption is occurring. Ideally, separate vineyards would be required to adequately test the number of twist ties required. The number of twist ties required to obtain mating disruption has never been determined. The labeled requirement of 100/acre appears to based on previous studies with Isonet Z that used 100/acre and not on any scientific results. No published study to date other than the current NE-SARE project has used Isomate GRB. Three earlier studies in 1986 through 1989 all used 100 twist ties per acre with different pheromone combinations than that found in Isomate GRB.1 Isonet Z twist ties have been used in studies from 2003 to 2011.2

The number of male grape root borers captured in the standard traps did decrease with Isomate GRB. In 2016, 313 were captured as compared with 388 in 2013, the year before the use of Isomate GRB. Statistical results were inconclusive. If the total grape root borers captured in 2016 is compared to the totals captured from 2009 to 2013, when 27 traps were also used, the number is significantly different at a 5% level using a two tailed single sample t test. When the results from 2016 are compared to the total captures for 2003 to 2013, no significant difference was found using a two tailed single sample t test.

The influence of Isomate GRB did not extend beyond the vineyard. Low levels of male grape root borers were captured in standard pheromone traps just 200 feet from the vineyard and would also indicate the moths within the vineyard are not attracted to traps placed outside the vineyard. The presence of female moths, Isomate GRB and other pheromone traps in the vineyard would seem to keep the moths within the vineyard. The higher number of moths captured at 1000 feet south of the vineyard might indicate they could be attracted from at least 1100 feet away, the closest source of wild vines and permanent vegetation to that trap.

The rate of pheromone loss from Isomate GRB twist ties is slow enough that they will easily last a season. In 2014 the loss was 0.274 milligrams per day and in 2015 the loss was 0.254 milligrams per day. At that rate, on average, half of the pheromone mixture would be gone after 152 days.

To fully evaluate the effectiveness of Isomate GRB, the project should continue another year.

Like many pheromone studies, this experiment gave inconclusive results. The number of male grape root borers captured did decrease after the use of Isomate GRB. With one data set the results were statistically significant, but with a different data set the results were not statistically significant. Various unknown environmental factors could also be partly responsible for any variation in the population.

1Williams, R. N., and J. L. W. Keularts. 1989. Occurrence and control of Vitacea polistiformis (Harris) (Lepidopter: Sesiidae) in Ohio vineyards. Ohio J. Sci. 89(2):4

Webb, S. E. 1991. Management of grape root borer in Florida with a pheromone. Proc. Fla. State Hort. Soc. 104:3-5.

Johnson, Donn T., Barbara A. Lewis, and J. Wendell Snow. 1991. Control of grape root borer (Lepidoptera: Sesiidae) by mating disruption with two synthetic sex pheromone compounds. Environ. Entomol. 20(3): 930-934.

2 Johnson, D. T., C. R. Roubos, T. W. Nyoike, L. L. Stelinski, and O. E. Liburd. 2013. Lures, Mating Disruption and Mass Trapping of the Grape Root Borer. Acta Hortic. 1001:129-137.

Pfeiffer, D. G., C. A. Laub, T. A. Jordan, A. K. Wallingford, and M. Cassel. 2010. Control of grape root borer using mating disruption – 2009. Proceedings of 85th Cumberland-Shenandoah Fruit Workers’ Conference, 19-20 November 2009, Winchester, VA. pp. 35-36.

Weihman, S. W., and O.E. Liburd. 2006. Mating disruption and attract-and-kill as reduced-risk strategies for control of grape root borer Vitacea polistiformis (Lepidopter: Sesiidae) in Florida vineyards. Fla. Entomol. 89(2): 245-250.

Participation Summary
1 Farmer participating in research

Education & Outreach Activities and Participation Summary

1 Curricula, factsheets or educational tools
1 Webinars / talks / presentations
3 Workshop field days
1 A website for the grape root borer research has been created, www.graperootborer.com.

Participation Summary

125 Farmers
5 Number of agricultural educator or service providers reached through education and outreach activities
Education/outreach description:

On August 20, 2014, a half hour presentation on the results from the project for 2014 was given at our farm. Background information on the life history of grape root borer was also presented. Pesticide credits were available for Pennsylvania and Maryland residents. The results from the project for 2015 were given at another half hour presentation on August 20, 2015 at our farm. Pesticide credits were available for Pennsylvania and Maryland residents. A final one hour presentation on the project was presented at our farm on August 24, 2016. The results and other information on grape root borer was discussed with the attendees. Pesticide credits were again available for Pennsylvania and Maryland residents.

On February 1, 2017 a 30 minute power point presentation, titled Can Grape Root Borer Be Controlled with Pheromones? was given at the Mid-Atlantic Fruit and Vegetable Convention in Hershey, Pennsylvania. Approximately 100 people were in attendance.

A website, www.graperootborer.com, has been developed to make the results of this project available to anyone. Information on the other NE-SARE projects related to grape root borer and general information on grape root borers has also been included on the website.

Learning Outcomes

10 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation
Key areas in which farmers reported changes in knowledge, attitude, skills and/or awareness:

Many grape growers are unaware of the damage grape root borers can cause in a vineyard. The project allowed them to evaluate the efficacy of Isomate GRB in regards to controlling grape root borer.

Project Outcomes

Assessment of Project Approach and Areas of Further Study:

The use of pheromones for insect pest control can create its own special problems. Because of the volatile nature of pheromones it became impossible to determine what level of Isomate GRB was required to control grape root borer. If using trap shutdown as a parameter for measuring the success of Isomate GRB, shutdown did occur at much lower densities than the recommended amount. An additional method of determining the success of pheromone treatments would be counting pupal cases under a selected number of vines in each treatment area and the control. Continued research into the viability of grape root borer control with Isomate GRB is recommended. In our project by one measurement the Isomate GRB did significantly reduce the number of grape root borers while with another set of data there was no significant difference. The use of this method for grape root borer control should be approached with caution and with the understanding it might not dramatically reduce the number of grape root borers, particularly if high densities of grape root borers per acre are already present. Isomate GRB might be more effective with a low population density, like that found in a recently planted vineyard.

Project results have been presented at a large regional conference that was attended by individuals from several regional universities. University and extension personnel will be notified about the website that will be available to all grape growers where grape root borers are a problem.

The results of this study would indicate that Isomate GRB is a not a panacea to rid a vineyard of grape root borer. The product should be used with the understanding that the reduction in grape root borer might not be substantial. Because of the expense of the product, more testing should be done to determine the exact quantities needed for suppression of grape root borer. The product definitely warrants further study to determine its long term effectiveness in reducing GRB.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.