Trap cropping for flea beetle control in long-season brassicas

Final Report for ONE06-063

Project Type: Partnership
Funds awarded in 2006: $9,133.00
Projected End Date: 12/31/2007
Region: Northeast
State: New York
Project Leader:
Molly Shaw
CCE Tioga
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Project Information

Summary:

Crucifer flea beetles are a consistent pest of Brassica crops in the Northeast. They emerge every year in the early spring and, unless controlled adequately, cause economic losses every year. Emerging summer adult flea beetles also cause damage to fall Brassicas that are planted in late July and August. Their feeding damage may defoliate seedlings, severely stunting their growth, and result in unmarketable leafy crops. The control methods currently utilized by organic farmers, such as row cover, are expensive and difficult to use, especially in long-season Brassicas that require several cultivations for weed control and may be harvested over a long period of time.

It has been observed that flea beetles find Brassica oleracea, which includes most of the traditional European crops such as cabbage, broccoli, cauliflower, kale and collards, significantly less attractive than Brassica rapa crops, which include many of the greens (bok choi, tatsoi, mizuna, etc). In spring, beetles colonize the crop from overwintering sites outside the field. This trial tested whether the beetles’ preference for Komatsuna (a Brassica rapa) could be used to in a perimeter trap cropping system to prevent beetles from colonizing a main crop of Brassica oleracea, resulting in less damage to the main crop and less need for insecticide sprays.

Komatsuna was planted as a “trap crop” border surrounding various Brassica oleracea crops. Beetle populations were controlled in the borders using Entrust, an organically approved form of spinosad. The protocol called for sprays to be applied as soon as beetles appeared, and weekly thereafter.

We established that flea beetles are more attracted to Komatsuna than to B. oleracea crops, and that Entrust does kill flea beetles. Transplanting the Komatsuna at the same time as the crop was the most successful way to establish the trap crop, as compared with direct seeding. Transplanting ahead of crop establishment had mixed results. Growers found it difficult to apply border sprays as promptly or regularly as needed in order to prevent flea beetle movement into the field. Waiting for flea beetles to build up in the border resulted in their rapid movement into the main crop. Frequent and excessive rains in May and June 2006 made timing of sprays more difficult. Where beetle pressure was low to moderate and the border was transplanted, the main crop did not require sprays. Where beetle pressure was high, and sprays were delayed, the main crop did require a full field spray for flea beetles or, in the case of a direct-seeded crop, the border was destroyed at the cotlyedon stage. Trap crop borders require a different kind of management, such as careful timing of planting and integrity of the borders, as well as attention to border sprays, in order to work effectively.

Project Objectives:
  • Establish borders of Komatsuna around Brassica oleracea crop plantings.

    Determine whether Komatsuna is more attractive to flea beetles than the main Brassica oleracea crop by monitoring leaf damage and beetle trap catches.

    Test whether surrounding a main Brassica oleracea crop with Komatsuna decreases the beetle population and damage in the main crop. Since these trials were done on working farms, we did not have separate control plots.

    Determine if a trap crop system for controlling flea beetles in Brassica oleracea crops is a viable pest control option for commercial farmers (economically feasible).

Cooperators

Click linked name(s) to expand
  • Chaw Chang
  • John Hayden
  • Ruth Hazzard
  • David Marchant Jane Sorensen
  • Ryan Voiland
  • Pamela Westgate

Research

Materials and methods:

Komatsuna was planted as a perimeter trap crop around Brassica oleracea at three locations in 2006, in NY, MA, and VT.

In each location, a double row of Komatsuna (B. rapa) plants was established around the main crops, which consisted primarily of Brassica oleracea such as kale, broccoli, brussels sprouts, and collards, creating a perimeter trap of attractive Komatsuna. In one field, several rows of Napa cabbage (B. rapa) were planted in rows within the center of the main B. oleracae crops.

When beetles were found in the borders, they were sprayed with Entrust (3 oz/A). The protocol called for sprays to be applied as soon as beetles appeared, and weekly thereafter; however, in several cases border sprays were delayed or separated by more than one week. The whole field was sprayed if beetle damage on the crop plants was above individual grower tolerance (we had no scientific threshold to work with).

The flea beetle population was monitored by using 3”x5”yellow sticky cards on 12” wire stakes placed vertically in row. Eight cards were placed along the border and eight were placed within the field. Cards were counted and replaced twice per week until the plants were well established, after about 4 weeks in each field. Flea beetle activity was also assessed by counting feeding holes on five leaves (same age leaves, from different plants) at each of eight randomly selected sites in the border and eight sites in the main crop. Leaves with >30 holes were given a score of 30, except in VT, where up to 50 holes per plant were counted (see Appendix A). Each week feeding hole sample sites were newly randomized, but yellow sticky cards remained at the same locations.

The border establishment trial was done in NY. We had three plantings of the main crops on which we tested the three border establishment methods. We direct seeded Komatsuna in the spring (April 13) three weeks before the first transplanted crop was planted. We transplanted Komatsuna around the crop at the time of the second planting (June 1, transplants were sprayed with Entrust before they were set out), and we transplanted the border on June 15, well before the main crop was planted for the third planting. In MA, in Field 1, the transplanted border was established around the whole field at the same time as the first planting (Jun 19), which filled about half of the field. Beds were established in the whole field. A second planting (also transplants) was set out 3 weeks later (July 3) inside the perimeter.

Specific details from the trial methods are included as Appendix A, which can be requested from Northeast SARE

Research results and discussion:
Results of establishment trials:

We were interested in direct seeding the border because it takes far less labor than transplants. However we found that direct seeding Komatsuna when flea beetles have access to the plants does not work. The flea beetles decimated the tiny Komatsuna cotyledons and the planting failed.

Transplanting the border at the same time as the main crop worked well and was the method of establishment in MA and VT. Seeding in the greenhouse should be timed so that the Komatsuna transplants are at least as big as the crop transplants at the time of setting out. Komatsuna that was seeded in the greenhouse at the same time as the main crop was big enough for transplanting at the same time. Two of the three growers in the project routinely use transplants for their Brassica oleracea crops so this did not require a significant change in management, only additional planning and greenhouse space.

In NY, we were not able to determine whether establishing the border well before transplanting the crops would work, because the third crop planting was never successfully established. In MA, the second planting within a large border (Field 1) appeared to be adequately protected. A potential problem with border establishment before crop establishment is that it may be difficult to get the whole field plowed and fitted, and all the beds established as needed, several weeks before the main crop is planted. Also, the ends of the borders tend to get destroyed while the crop beds are being prepared. New Komatsuna transplants would have to be planted to fill in these gaps. A pre-established border may provide an opportunity for stale seed-bedding as well as having a very attractive trap crop border in place at the time of crop establishment, but we were unable to fully test this idea.

Timing of border sprays and need for main crop sprays:

Border sprays were applied anywhere from 3 to 14 days after beetles arrived in the border. In MA, this delay was a choice made with the grower, based on very low beetle pressure. Border sprays were applied when beetle damage exceeded 2 holes per leaf in the border. In NY, the reason for the delay may have been a combination of rainy weather, and unexpectedly rapid arrival of beetles. In VT transplanting was delayed for two weeks by a long period of rain. After transplanting (May 30), beetles colonized both the border and main crop within one day after transplanting, reaching estimated levels of 10 per plant and requiring a full field spray. Two subsequent sprays were applied only to the border. After five weeks, when the border was mowed, the grower noticed an increase in beetle population in the main crop of collards.

Results of beetle food preference observations:

In NY, we found that Komatsuna border was more attractive to flea beetles than the main crop. Although the numbers of beetles caught on sticky traps in the crop was sometimes higher than in the borders, there was always more feeding damage in the Komatsuna border than in the crop in the second planting (graphs can be supplied by SARE).

The third planting (no crop established) had high feeding damage levels on the border, but trap catches were low (August 17-Sept 19). This is consistent with other observations that after September 1, flea beetles are no longer highly attracted to yellow and have a lower propensity to feed.

In MA, beetle pressure overall was low. Assessment of beetle preference is complicated by the fact that borders were sprayed, while the main crop was not. The exception was a main crop spray for thrips, three weeks after the crop was planted in field two. Prior to border sprays, feeding damage was higher in the border than on the main crop; after, it was sometimes higher in the main crop but remained below 3 holes per leaf. Trap catches were similar in border and crop, except in the second planting after the main crop (but not the border) was sprayed with spinosad (Entrust) to control thrips.

In VT, feeding damage was consistently higher in the Komatsuna than in the collards. Feeding damage remained higher even after border sprays. After the first week of the trial, sticky card counts were slightly higher in the Komatsuna also.

Assessment of beetle damage decreases caused by trap crop:

Given the inability to establish control plots on cooperating farms, determining definitively if the presence of the trap crop decreased the amount of damage that would have occurred on the main crop was the most difficult aspect to evaluate. In all of the fields the attractive border concentrated flea beetles, as shown by the higher feeding damage in the border (Figures, in Appendix).

In NY, the main crop of the second planting exceeded the tolerable level of flea beetle damage, but the border was not faithfully sprayed. The few crop plants in the third planting did get some flea beetles on them even though the border was sprayed faithfully for a month, but rain often washed off sprays.

In MA, border sprays were used and the flea beetle pressure in the main crop never reached levels great enough to cause the grower concern. However, it would be difficult to deduce from these plantings the effectiveness of the Komatsuna border against high flea beetle pressure, because the flea beetle numbers in these were relatively low.

It can be seen in both MA plantings, however, that having an attractive border can concentrate flea beetles, and that border sprays will have a positive effect on decreasing the feeding damage and flea beetle counts in the main crop. It is probable that the rotation schedule that the grower used was the main cause of the low flea beetle numbers. Both fields were well away from the early season brassicas, which had been bombarded with flea beetles. Due to the risk, this grower was not willing to try the PTC crop around his early brassicas; he uses row cover on early Brassica crops.

In VT, the main crop and border were both sprayed soon after transplanting, but while the border was sprayed twice more during the season, another full field spray was not required to keep damage down to a tolerable level.

Determination whether trap cropping for flea beetle control is a viable pest control option for farmers:

Econommics: SARE can provide a table (Table 1) summarizing the costs of the trap cropping system.

Table 1 shows the potential costs of materials of three different flea beetle management strategies. Material costs could be reduced by using a perimeter trap crop spray. The cost per acre for materials depends on the size and shape of the field (the larger and more square the field, the less cost/acre of cash crop to spray the perimeter). In our trials the cost/acre ranged from $8.50-$24 per application. This is a savings from the $85/acre to spray the entire crop. Depending on flea beetle pressure, a grower could estimate 3-5 sprays for the crop. Using a row cover as an insect barrier would cost approximately $461/acre for a one time purchase of the material.

Labor costs are reflected in the management intensity. The row cover takes high management and labor as it needs to be laid out, secured and then moved for cultivations and harvest. The trap crop strategy takes more management than spraying the entire crop at the recommended rate of 3 oz/acre because of the planning and planting of the perimeter, but less time to spray. If the trap crop is not marketable, then the grower gives up potential ground for the cash crop by planting a perimeter.

More trials would need to be done to determine the effectiveness of each strategy and overall economic return.

Farmer conclusions:

In NY, the farmer decided that he did not want to try the trap crop system again on his farm. He was hoping the trap crop would take less management than floating row cover, but because of the importance of careful timing to manage the trap crop, he decided that to successfully manage a perimeter trap crop for flea beetle control would actually take more management than using row cover, at least when flea beetle pressure is high like it is on his farm. At least it would take a different set of management skills than he already has developed.

In MA, the grower is interested in trying the PTC system again next year with napa cabbage as the trap crop around the less attractive Brassica oleracea crops. In 2006, neither field required sprays to reduce flea beetle feeding damage. Komatsuna was harvested in both fields, and the napa cabbage was harvested, as well. The grower had difficulty marketing the Komatsuna- it was not popular with customers; however, the napa cabbage, which is also highly attractive to flea beetles, is very marketable.

In VT, it was difficult to determine the effect of the Komatsuna PTC without a control to compare results to. Our results did show that it was not totally effective. The grower will probably not use the PTC method again next year. He was interested in the idea of a physical barrier of winter rye used in conjunction with a trap crop around the border of the field.

Lessons learned:
  • The border will concentrate and delay flea beetles from entering the main crop, but not prevent them from moving into it and feeding.

    Entrust does kill flea beetles. Where it was used the amount of flea beetle damage decreased; however, it was not a cure that totally eliminated beetles, particularly when the populations were high and beetles continued to move into the field. Attention to consistent border sprays (at least weekly) could have reduced the damage to the main crop more than was observed in some fields.

    Using transplants worked well, where both the border and the main crops were transplanted at the same time. Crop establishment was not a problem with transplants, but establishment by direct seeding in the spring failed without providing flea beetle protection for the emerging plants as they established. Establishing a border weeks before establishing the crop was problematic where the main field was direct seeded. It worked well in a field where a second transplanted crop was placed inside the field perimeter three weeks after the first crop and the whole perimeter were established. This could be applied to succession planted brassica crops, if the grower is able to prepare the entire field at the time the first crop is planted. Careful attention to protecting the border on the ends of the rows is needed.

    Once established, Komatsuna grows vigorously and keeps up with B. oleracea crops, even under heavy flea beetle feeding. New growth in the center of the plant remains attractive to flea beetle for many weeks after planting.

    Same spacing was used for Komatsuna as for main crops (in-row and between row). Use of a double row of Komatsuna helped ensure a strong border.

    Ends of rows were sometimes destroyed by cultivation; it is important to use 2-3 plants at ends of rows and take care not to run them over.

    The trap crop should not be removed before the main crop is finished or past the susceptible stage. In VT, removing the trap crop seemed to result in an increase in flea beetle damage on the main crop.

    Combining perimeter trap cropping with crop rotation to reduce the flea beetle population is helpful. In MA both fields were separated from early spring brassicas (greens and cole crops) where flea beetle pressure had been very high.

    Imported cabbage worms are not controlled by a Komatsuna trap crop. The grower should plan for their management separately from the flea beetles. Onion thrips were a problem in a late brassica field that was adjacent to the onion field. When onions matured, thrips built up in the Brassica crop and required an application of spinosad.

    Trap crop borders take careful management, from establishing and maintaining the border integrity, to using the delay the border gives them by spraying that border on a consistent (weekly) basis—growers should plan for this management and be prepared to do things a little differently to make the system work effectively.

Research conclusions:
Efficacy of Komatsuna trap crop in decreasing flea beetle damage to the main Brassica crop

Given mixed results and many lessons learned, we can recommend this perimeter trap crop system as an experimental management practice, provided that growers are able to implement the steps needed to make it work: establish a healthy and complete border at the same time as the main crop (preferably, transplanted not direct seeded), and spray the border promptly and regularly. We would also recommend that this practice be combined with other cultural tactics to reduce flea beetle populations, including a rotation plan.

Growers should not expect the perimeter to provide control without spraying, nor that even a sprayed border will provide complete control of very high beetle populations. However, given the positive cost benefit combined with moderate management intensity, and the need for alternatives to row cover and full-field sprays, we would encourage growers to test it on an experimental basis. We also would like to see further experimental evaluation that includes control fields without a trap crop border for comparison.

Disseminating project results will likely cause other farmers to think about the concept of perimeter trap cropping as well as crop rotation and use of transplants as part of an IPM system to decrease pests and the need for full field sprays. This trial showed that testing Komatsuna as a trap crop around Brassica olearcea can be accomplished with low risk if the grower is prepared to spray borders promptly and monitor carefully, and that it shows promise especially if combined with other cultural practices. It also demonstrated that on-farm research is useful and can provide results grounded in the farming reality. The trial also reaffirmed the importance of field rotations in controlling flea beetles, and gave a basis of experience with perimeter traps to control flea beetles that can be used by other innovative farmers to plan their own trials.

Participation Summary

Education & Outreach Activities and Participation Summary

Participation Summary:

Education/outreach description:

We will convey to growers the salient points we learned about this trap crop system, especially how NOT to manage a trap crop, and individual farmers can decide for themselves whether or not it is something they would like to do on a trial basis.

Results of this project will be disseminated through newsletter articles (reaching 1900 growers) and through personal contacts in the years ahead.

In NY, the newsletter article in the Southern Tier Produce News will reach about 200 growers.

In VT, an article will be written for the 1200 member distribution of the NOFA-VT newsletter on the PTC concept in general with a mention of what was seen in this trial.

In MA, the VegNotes newsletter distribution is 500.

Project Outcomes

Project outcomes:

SARE can provide a table (Table 1) summarizing the costs of the trap cropping system.

Table 1 shows the potential costs of materials of three different flea beetle management strategies. Material costs could be reduced by using a perimeter trap crop spray. The cost per acre for materials depends on the size and shape of the field (the larger and more square the field, the less cost/acre of cash crop to spray the perimeter). In our trials the cost/acre ranged from $8.50-$24 per application. This is a savings from the $85/acre to spray the entire crop. Depending on flea beetle pressure, a grower could estimate 3-5 sprays for the crop. Using a row cover as an insect barrier would cost approximately $461/acre for a one time purchase of the material.

Labor costs are reflected in the management intensity. The row cover takes high management and labor as it needs to be laid out, secured and then moved for cultivations and harvest. The trap crop strategy takes more management than spraying the entire crop at the recommended rate of 3 oz/acre because of the planning and planting of the perimeter, but less time to spray. If the trap crop is not marketable, then the grower gives up potential ground for the cash crop by planting a perimeter.

More trials would need to be done to determine the effectiveness of each strategy and overall economic return.

Assessment of Project Approach and Areas of Further Study:

Areas needing additional study

Future Recommendations

This project laid the groundwork for a trial with a control plot, to statistically determine if the presence of a well-managed Komatsuna border decreases flea beetle damage in a brassica crop. We learned how NOT to manage a Komatsuna border, and spotlighted methods that would likely have the greatest chances of success. More research needs to be done to determine if it works well enough under all flea beetle populations, and what specific practices are needed, to make it worth the extra time and cost necessary to learn how to establish a PTC.

The following recommendations are for growers who wish to try this method on their own:

1. Rotate
Moving a new crop planting far away from a previous brassica crop and from brassica weeds is a simpler and more effective way to avoid flea beetle damage to brassica crops than using a trap crop with little distance between plantings. If a farm has enough land, try rotating long distances. Using a Komatsuna border may complement this approach and provide additional protection at a lower cost than full field sprays.

2. Establish and maintain border integrity
Establish the integrity of the border before or as the main crop is planted into the field. Make sure there is a full border (2 rows recommended) around the entire crop. Care should be taken on curved fields that no gaps in the border spacing exist. Make sure border plants at the ends of the rows remain. It is a good idea when transplanting to have extra Komatsuna transplants to fill in gaps or lost plants. Don’t harvest the border until you are comfortable with flea beetles moving into the main crop.

3. Spray early
Remember that the Komatsuna will not prevent the flea beetles from moving into the main crop, but that it will delay them and give a time window and location to kill them before they move to the main crop.

Sprays need to be timed to prevent flea beetle movement into the field. DO NOT wait for flea beetles to build up in border; spray border when beetles first appear. This may be the same day as planting, if pressure is high. Alternatively, spray transplants in the trays before planting into the field. For extra insurance and with minimal material use, crop transplants could be sprayed once before planting as well.

4. Spray consistently
Weekly sprays of the border will keep the flea beetles from moving into the main crop. For flea beetles on Komatsuna, Entrust should always be present on the plants so the border is both attractive and lethal. A spreader-sticker would help keep the Entrust on the Komatsuna, especially during a rainy growing season like 2006. Try to get good coverage of the Komatsuna when spraying.

Remember that this method is new to you and may take some practice before you get it right. While it can initially take more work because you are learning a new way of managing the crop, ultimately, if it works, it could save time and money.

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.