Developing Sustainable Management Tactics for Cucumber Beetles in Cucurbits
The cucurbits (cucumber, melon, squash, pumpkin, etc.) are exceptionally diverse and valuable commodities grown on many farms in the Northeastern and across the US. Cucumber beetles are considered a serious pest of cucurbits, and growers often take a conservative approach and treat frequently with insecticides to control these pests. Organic growers rank cucumber beetles as the most important insect pest of cucurbits. The goal of this project was to develop environmentally benign and cost-effective management tactics for cucumber beetles.
To reach our objective we developed a trapping system for cucumber beetles and investigated trap crops and cultural practices to improve beetle management.
We found that attractant-baited traps containing a very small amount of insecticide showed promise for mass-trapping adult beetles under field conditions. Up to 65% of the beetles were removed using this tactic. This trapping system is unique in that it requires very little toxicant, the toxicant is removed from the field after a relatively short time, and none is applied directly to the crop.
The research also showed that a highly preferred trap crop in combination with a few attractant-baited traps will significantly reduce the number of beetles (more than 75 percent) and injury to less preferred cucurbits. Trap cropping and mass trapping were tested on commercial vegetable farms in central New York. Due to low beetle densities at test sites, however, we were not able to fully demonstrate the potential of these tactics. On-farm trials did show that these tactics, in particular trap cropping, would be very practical and cost effective for growers.
To determine the potential of fall cultivation as a means of suppressing overwintering beetles, we monitored beetle populations in and around cucurbit fields until the onset of winter. Results indicate that populations aggregate on remaining green vegetation and fruit where control could be focused in the form of spot treatments with insecticide or physical destruction with deep plowing. Trials simulating deep plowing showed that about 45 percent of beetles are killed if buried 6- and 12-inches deep, but none survive if buried at 18 inches.
Our field work also demonstrated that attractant-baited traps after harvest have potential for suppressing overwintering populations. Suppression of immature cucumber beetles with entomopathogenic nematodes appears possible and could be especially effective if applied to trap crop plants to control progeny of aggregated adults. Tests on the effectiveness of insecticides used by organic farmers showed that rotenone was better then cryolite or neem. Results indicate that feeding stimulants enhanced the effectiveness of rotenone, permitting the use of reduced rates.
The use of trap cropping and cultural controls for suppression of cucumber beetles will result in significant reductions in the amount of insecticide used for managing cucumber beetles. This will save growers money and minimize risks to the environment.
Interest in our research was strong. Over 400 growers, extension staff and other agricultural professionals attended workshops, seminars and field days associated with the project.
1. Develop trapping techniques to control early season infestations of cucumber beetles.
2.Develop cultural and biological control methods for control of cucumber beetles.
3.Improve the effectiveness of botanical insecticides.
A mixture of cucurbit blossom volatiles (TIC) is an effective attractant for cucumber beetles and rootworms when used in traps (Levine & Metcalf 1988 and others). We have improved the effectiveness of such traps through a series of studies (Hoffmann et al. 1996a).
In an effort to find a better trap for cucumber beetles we investigated several designs, including a design that only requires beetles to land on the trap. Upon landing on the trap the beetles pick up a small dose of toxicant or spores of an insect pathogen. This design results in rapid control from the toxicant adhering to the beetle or slower control via infection by the pathogen. In this unique scenario it should be possible to trap enough beetles (mass trap) to reduce damage. The advantages of this tactic include: an extremely small amount of toxicant is used; the toxicant does not contact the crop; and, the toxicant is removed from the field after a relatively short time and properly disposed elsewhere.
We found that the most effective toxicant was a solution of carbaryl (0.3% ai) in mineral oil. For example, at 10 traps per acre this translates to 0.0022 lbs. active ingredient per acre. This is a 99% decrease over a traditional insecticide application. Thus this method could considerably reduce the amount of insecticides used for managing cucumber beetles. For organic growers the synthetic toxicant could be replaced with one appropriate for their needs. However, our trials showed that the traditional insecticides most often used by organic growers were only marginally effective when used in traps. Although slower in rate of control, a pathogen-containing trap may be best for organic systems.
Our studies indicate that with little modification these traps will be effective in mass-trapping striped cucumber beetle population, both during early and late season, using an extremely small amount of toxicant. We have demonstrated that traps are effective, but they need to be made more durable and able to remain effective under even adverse environmental conditions.
Cucumber beetle management can also be improved through the development of cultural and biological control tactics. Certain types of cucurbits are highly preferred by cucumber beetles and these preferred types could aggregate beetles and their progeny for more efficient control. Our ongoing cucurbit screening and breeding program with Dr. Molly Kyle, Dept. of Plant Breeding, Cornell University, focuses on developing resistance to beetle pests and has identified highly preferred genotypes for use as trap crops (Hoffmann et al. 1996b, Reiners et al. 1999). The potential for spring trap crops has been further supported by work in Maine (Radin & Drummond 1994) and more recent work in Oklahoma (Pair 1997). Trap crops could be further enhanced by the addition of the long-range attractant (TIC).
The results of our experiments show that trap cropping is effective in reducing the injury caused by striped cucumber beetle adults to pumpkin seedlings at their early stages of development. Also, the addition of traps with TIC lures attracts and kills many adult beetles thereby reducing the population of striped cucumber beetle adults in the field.
In addition to trap cropping, cultural practices such as fall cultivation may affect survival of overwintering cucumber beetles. The beetles present in the field late in the summer and fall, overwinter to infest fields the next spring and their control could minimize infestations the next season. Our objective was to monitor the fall population of beetles and also to study the effect of fall cultivation and fall clean-up on the beetle mortality.
We set up simulated cultivation trials under greenhouse conditions. We used 2 ft long sections of PVC pipe and buried fifteen beetles at 6, 12, and 18 inches below the soil line (to simulate burial by different cultivation tactics). Also, the effect of fall clean-up was tested by including plant debris or no plant debris on top of the soil in PVC pipes. Each treatment was replicated 5 times. The top and bottom of the PVC tubes were covered and the number of beetles surviving was recorded two weeks later. Results showed that 58 and 61 percent of beetles that were buried under 6 and 12 inches, respectively, were able to crawl up to the soil surface and survive. However, none of the beetles that were buried at the 18-inch depth made it to the surface. This shows that deep cultivation in the fall can cause mortality and should help reduce overwintering populations. Shallower cultivation will also result in some mortality.
Suppression of immature cucumber beetles with entomopathogenic nematodes appears possible and could be especially effective if applied to trap crop plants to control progeny of aggregated adults. Unfortunately, the commercial nematode industry has dwindled drastically since this project started and we have not been able to obtain commercial formulations of the nematode species that we intended to test.
We also did studies aimed at improving the effectiveness of botanical insecticides. The results of our experiments show that all the botanicals tested caused a reduction in the damage caused by beetles. Rotenone at full (with and without the feeding stimulant) and 1/2 rate (with the feeding stimulant) had the lowest damage and highest beetle mortality. The addition of feeding stimulant seemed to enhance the effectiveness of rotenone and permitted its use at half the full rate without significant reduction in the effectiveness. However, feeding stimulants did not alter the effectiveness of cryolite. Neem did not have any significant effect on the beetle survival or mortality but being an antifeedant it significantly reduced damage caused by beetles to plants. Overall, rotenone at 1/2 rate + feeding stimulant gave good control which permits reduced rates of rotenone.
Field activities have been conducted at the Department of Entomology Farm, Freeville, NY. In addition, trials on trap cropping, mass trapping and fall cultural practices were conducted on cooperating farms (all in New York) including Iron Kettle Farm, Candor, Strawberry Valley Farm, Whitney Point, Stoughton Farm, Newark Valley, Blue heron, Lodi, and Early Bird Farm, Ithaca. These farms represent the typical diverse vegetable farms common throughout the northeastern US. They included both conventional and organic farms.
Trap cropping and use of TIC traps is relatively effective against adults of striped cucumber beetles. The use of trap cropping would be more feasible for small growers who normally plant many varieties of cucurbits on their farm. The cost involved should be minimal because all that is involved is rearranging specific crops (preferred and non preferred) which most plant anyway. Relative preference of 59 cultivars of cucurbits is available to growers in the 1999 Cornell Recommendations for Vegetables (Reiners et al. 1999). Likewise, the cost involved in fall cultivation should also be minimal. Most farmers cultivate their farms during late fall, advancing the time of cultivation a little earlier than their normal schedule would help in controlling overwintering populations, at almost no additional cost. The mass trapping method would cost about $23.60/acre (at 40 traps per acre). There would be an additional cost related to labor for trap installation. A single insecticide application costs about $19/acre, however it is not unusual for growers to apply more than one application for cucumber beetles. If traps were produced in large number the unit cost would decrease considerably and be more competitive with a single insecticide treatment.
Because this was mostly a research effort we have yet to see the extent of farmer adoption of these practices. The on-farm demonstrations conducted on several farms should encourage consideration of these new practices. Growers were very interested in the project and were very willing to cooperate. The striped cucumber beetle is considered a serious pest and they want to have good management tactics for it.
It is important to point out that the squashes, watermelon and pumpkin are not highly susceptible to bacterial wilt (vectored by beetles) so plants can sustain some damage. In contrast, melon (muskmelon) and cucumbers are susceptible to wilt and far less damage can be tolerated. Consequently, the users of the following tactics need to be aware that they will help suppress infestations, but especially for wilt susceptible varieties, may not provide sufficient control to prevent the occurrence of bacterial wilt.
1. The use of trap crops is relatively easy and recommended. The choice of cultivar can be made by reference to Reiners, S., C. H. Petzoldt, M. P. Hoffmann and C. C. Schoenfeld. (eds.). 1999. Integrated crop and pest management recommendations for commercial vegetable production. Cornell Cooperative Extension or the equivalent web site http://www.nysaes.cornell.edu/recommends/. In the cucurbit section there is a list of 59 cucurbit cultivars and their relative preference by cucumber beetles. This list can be used to select types less preferred, as a means of reducing damage, or for selection of highly preferred types for use as trap crops. Beetles aggregating on the trap crop can be controlled with insecticides or traps can be installed in the trap crop to kill colonizing beetles. The trap crop should be overseeded to prevent total destruction by colonizing beetles.
2. Mass trapping of beetles also holds potential. We recommend 40 traps per acre, but fewer may also provide relief from infestations, especially if control options are limited. At present, no commercial company produces the traps or formulates TIC lures, so the availability of this tactic is limited. A back up trap design would be the same yellow cup described above, but coated with sticker. Even without TIC these traps will catch many beetles.
3. Timely destruction of crop residue and deep cultivation will help suppress overwintering populations. This should also be relatively easy to accomplish and requires little extra work or time. Spot treating (targeting beetle aggregations) of fields in the late summer and fall should also help. Some growers already practice this. Lastly, the use of attractant-baited traps late in the fall and when the vegetation is mostly dead should also help suppress fall populations.
4. Organic growers can reduce the rate of rotenone applied by adding buffalo gourd root powder, a feeding stimulant, to the insecticide. This does not constitute a recommendation. Check with the state lead agency for pesticide registration to insure the legality of modified use of rotenone.
The use of entomopathogenic nematodes is possible, but their commercial availability is limited. An efficient use of these relatively expensive agents, would be to apply them only to trap crops, where we believe more cucumber beetles would be lay eggs because of the aggregations of adults on these plants. Larvae hatching from eggs would be controlled by nematodes.
Areas needing additional study
The overwintering behavior of cucumber beetles and the mechanism by which cucumber beetles locate and aggregate on host plants need additional investigation. Work currently underway has determined that male striped cucumber beetles release an aggregation pheromone that attracts large number of male and female beetles. The identification of the chemical nature of this pheromone and it synthesis for use in traps or as baits holds considerable potential. This compound is different than TIC now used in traps and we believe will be a far more potent attractant of beetles. Complimentary studies now underway and supported by a grant from the Northeast Regional IPM Program are addressing the economic importance of striped cucumber beetle feeding damage to young pumpkins and winter squash, as well as investigating the impact of larval feeding damage to cucurbit root systems and how this is affected by cucurbitacin content. These studies have also identified two, until now, unknown parasitoids of striped cucumber beetle. Levels of parasitism by these natural enemies is high (fig. 5) and no doubt important in helping suppress infestations. This is exceptionally interesting information, and with additional research may lead to enhanced biological control of this important pest. The parasitoids apparently use the newly discovered aggregation pheromone to find the beetle hosts.