This research project was designed to look at three commercially available organic sprays for control of adult flea beetles on arugula. In addition, these three sprays were also tested with a trap crop of Green Wave Mustard. The three sprays represented different approaches to flea beetle control: 1) a garlic spray was used as a deterrent to adult foraging and feeding damage, 2) Pyganic was used as a mortality agent against adults and 3) Brix Mix was used as a foliar plant feed to increase the health and resistance of plants. Control plots of no sprays were also used (both in conjunction with and without the trap crop).
We completed four replications of the experiment. The first replicate was planted in June 2004; the remaining three replicates were planted in September 2004. We measured the effectiveness of the control strategies in two ways. Each week we used a D-Vac to sample two 10-foot sections of arugula from each treatment and counted the number of adult flea beetles caught. Twice during the growth of the crop (14 days after germination and just prior to harvest) we assessed the amount of feeding damage on arugula leaves by adult flea beetles using a ranking system of: 0=no damage; 1=1-5 feeding holes; and 2=>5 feeding holes. The threshold of five feeding holes represents the cut-off between commercially marketable and un-marketable product. Five circular (1/3-meter diameter) quadrates were sampled per treatment-sampling day.
This research project was designed to look at three commercially available organic sprays for control of adult flea beetles on arugula. In addition, these three sprays were tested when used with a trap crop of Green Wave Mustard. We used a split-plot experimental design. Each spray was applied twice per week at the label recommended dosage levels.
Only the initial replicate (June-July) had significant amounts of adult flea beetles to test the different treatment combinations. The Green Wave Mustard was effective in attracting adult flea beetles to it at nearly a 2:1 ratio compared to the arugula crop. In addition, statistical results (repeated measure ANOVA) indicated a significant complex interaction between adult flea beetle abundance and both the trap crop and the organic sprays; however, the adult flea beetle populations ranged from 100 to 200 per 10-foot crop row for all treatments during the second, third and fourth (final) weeks of sampling. This level of adult flea beetle presence resulted in over 50% of all leaves sampled with flea beetle feeding damage to be rated as category 2 (non-marketable) for any treatment combination of spray and trap crop.
BENEFITS OR IMPACTS ON AGRICULTURE
Adult flea beetles are a devastating pest on most organic farms in the Puget Sound region of Washington. Several growers have been using one or a mixture of organic compounds tested in this research with varying degrees of success. The results from our experiment indicate that none of them will provide effective control when flea beetle populations are high. Given the overall poor performance of any treatment combination, growers will continue to look at alternative control strategies. Currently, the best control strategy is use of a physical barrier to feeding such as Remay cloth.
REACTION FROM PRODUCERS
During the July field day and presentation of results at the Washington and Oregon Tilth Meeting, most producers indicated agreement with the damage adult flea beetles do on their farms and the lack of control obtained from most non-physical barrier control strategies.
RECOMMENDATIONS OR NEW HYPOTHESES
Based on the results of this work, our recommendations are: 1) these treatments are not effective during high flea beetle pressure at the rates applied; 2) other research indicates that having a trap crop or deterrent crop closer to the cash crop may provide better control.
1) Field day: July 12, 2004, Washington Tilth Producer’s Crop Walk, Full Circle Farm, Carnation WA; approximate attendance was 20 producers and eight extension personnel.
2) Conference: November 12-14, 2004, Poster presentation at Washington and Oregon Tilth Conference, “T:30, Transforming the World One Fork at a Time: Our 30th Anniversary Conference & Celebration!”, Portland, Oregon; registered attendance was 650. The poster was also presented at the co-occurring “Making the Bugs Work for You: Biological Control in Organic Agriculture—WSU/OSU Research Symposium.” Conference proceedings handed out to all registered attendees included poster summaries. There were 160 in attendance.
3) Presentations: The results of this research will be part of the following presentation:
a) Washington State University King County Extension Education Night, “Flea Beetles: Biology and a Research Update on Organic Control Options,” December 8, 2004, Renton, WA.
b) Western Washington Horticulture Association Annual Conference, “Flea Beetle Control: Biology, Control Strategies & A Research Update,” January 11, 2005, Seatac, WA.