A comparison of the effects of different organic and sustainable non-crop vegetation and soil management techniques such as trap crops on striped cucumber beetle population dynamics. A Blue Hubbard trap crop provided some early season protection, but the trap crop effect broke down late in the season, and was not as effective a control method as floating row covers. Including a tomato intercrop or adding a cucurbitacin spray or a pyganic spray to the trap crop failed to improve the trap crop’s effectiveness. Data were gathered on MSU campus at the Student Organic and Horticulture farms.
In recent years there has been an increasing interest in, and demand for, organic produce (Tavernier 2003). Organic production faces many of the same pest challenges as conventional production, but often cannot incorporate conventional pest management solutions, which commonly focus on spraying crops with pesticides. Organic growers need to satisfy organic labeling restrictions which limit the types and amounts of chemical inputs (Phelan et al. 1995, Caldwell et al. 2005), often requiring them to employ different pest management techniques than conventional growers. In addition, some growers have a desire to grow fresh produce free of pesticide inputs, whether organic-compliant or not.
Cucumbers, Cucumis sativus L., are a major vegetable crop in the United States (Swiader and Ware 2002). The striped cucumber beetle, Acalymma vittatum Fabricius (Coleoptera: Chrysomelidae), is a major pest of cucumber. This pest is of great concern to vegetable growers in both organic and conventional production due to the feeding damage that adult beetles cause to the plant’s seeds, foliage, flowers, and fruit; the adults’ ability to vector bacterial wilt; and the larvae feeding on plant roots (Chittenden 1923, Foster et al 2005). Striped cucumber beetles overwinter as adults and emerge to feed early in the growing season, badly damaging or killing young cucurbit seedlings or new transplants. After emergence the adults feed and lay eggs in the soil around the base of their host plant. Striped cucumber beetles are univoltine in the north central United States, and can be bivoltine in the warmer southern gulf states (Chittenden 1923, Davidson & Lyon 1979, Capinera 2001). The larvae feed on roots, but they are less of a threat to cucumber production since they do not begin feeding until the plants are large and they do not transmit bacterial wilt (Chittenden 1923, Foster et al. 2005). The larva does not cause fruit scarring as long as the fruits are not in direct contact with moist soil (Chittenden 1923). The striped cucumber beetle host range covers most cultivated Cucurbitaceae, including squash, melons, and cucumbers.
While there are several insecticides available for striped cucumber beetle control (Bird et al. 2008), few are certified for use in organic production systems and, like other insecticides, they can harm beneficial organisms such as natural enemies and pollinators (Johansen 1977). In areas where bacterial wilt is infrequent, such as in many parts of the north central United States (Hayward 1991), cucumber plants can withstand up to 25% defoliation without exhibiting significant yield loss (Burkness and Hutchison 1998). In these conditions, organic-compliant techniques to manage cucumber beetle are possible and some, such as trap cropping, are employed with varying degrees of success.
Trap cropping is used in commercial settings for striped cucumber beetle management, but the technique commonly relies on the application of an insecticide to the trap crop once beetles are detected, which is not desirable for some organic producers (Hokkanen 1991, Javaid and Joshi 1995, Shelton and Badenes-Perez 2006). On muskmelons, C. melo L., 82% of northern corn rootworm, Diabrotica howardi Barber (Coleoptera: Chrysomelidae), and striped cucumber beetles were found on the trap crop rather than on the muskmelon crop (Metcalf 1985). In another study, striped cucumber beetle densities were 42% to 81% higher in an NK530 squash perimeter trap crop, Cucurbita maxima Duchesne, than in the main melon crop, C. melo L. (Caldwell and Stockton 1998, Caldwell et al. 1998). In an extension program, all participating growers stated that their pest control using a perimeter trap crop of Blue Hubbard squash, C. maxima Duchesne, around their green and yellow summer squash, C. pepo L., was “much better” than in previous years without a trap crop (Boucher and Durgy 2004). Radin and Drummond (1994) recorded that at least 70% of striped cucumber beetles were in a squash trap crop, C. maxima cv. ‘Sweet Mama’, compared to 30% in a cucumber crop. Squash trap crops also protect watermelon, Citrullus sp., and muskmelon, C. melo, from striped cucumber beetle (Cline 2004, Hoffman 1999). Blue Hubbard squash is a particularly promising candidate for a trap crop because striped cucumber beetles prefer it over most other cucurbit species (Reed et al. 1984, Pair 1997, Boucher and Durgy 2004, Shelton and Badenes-Perez 2006).
Increasing plant diversity in the field through intercropping and polyculture is an organic-compliant approach which can cause a 10 to 30 fold reduction in striped cucumber beetle populations compared to a monoculture (Bach 1980). The addition of a non-host tomato crop, Solanum lycopersicum L., to a field of cucurbits in some cases reduces the number of striped cucumber beetles present (Lawrence and Bach 1989). In comparison, trap cropping tends to be more effective at reducing phytophagous insect pest populations than intercropping (Banks and Ekbom 2004), but it is not clear whether in combination the effects are additive.
A trap crop’s attractiveness to an insect pest can sometimes be enhanced with biological attractants such as kairomones (Hokkanen 1991, Javaid and Joshi 1995, Shelton and Badenes-Perez 2006). The addition of biological attractants can significantly enhance trap crops in the control of the Colorado potato beetle, Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae) (Martel 2005). Kairomones that attract striped cucumber beetle and which may be useful in trap crop enhancement have been identified and are commercially available (Lewis et al. 1990, Fleischer and Kirk 1994, Brust and Foster 1995, Jackson et al. 2005). Attractive kairomones were used to enhance the attractiveness of sticky traps to reduce cucumber beetle populations by 50% by placing 40 kairomone enhanced sticky traps per acre around field edges (Hoffmann 1996). Such kairomones were also used in several different striped cucumber beetle baits (Fleischer and Kirk 1994, Burst and Foster 1995, Schroder et al. 2001, Martin et al. 2002, Jackson et al. 2005).
This study focuses on investigating organic-compliant non-insecticidal methods for managing striped cucumber beetles in cucumber production by increasing the level of plant diversity using a trap crop and an intercrop. Specifically, a comparison was made between the effectiveness of a squash trap crop, a cucumber and tomato polyculture added to the trap crop, and a squash trap crop with added biological attractants in reducing striped cucumber beetle densities on cucumbers. Floating row covers placed over the cucumbers and use of an organically approved insecticide were also included in the comparison of organic-compliant techniques.
Intermediate-term: Catalyzing co-learning, knowledge and innovation among organic and transitioning farmers, and improving the sustainability and profitability of cucumber production in the Midwest.
Short-term: A sustainable pest management plan for cucumber beetle using improved trap crop effects, adding to scientific and outreach literature, and generating informed discussion about sustainable approaches to agriculture among growers.
This study was conducted in 2006 and 2007 at an organic transition research plot and at the nearby student organic farm located at the Michigan State University Horticulture Teaching and Research Center in East Lansing, MI (42° 41’ N, 84° 30’ W). In the organic transition field site, ‘Cobra’ slicing cucumber and ‘Mountain Fresh Plus’ tomatoes (commonly used in commercial production) were grown in a 90 m x 34 m field in raised beds covered with plastic mulch and drip irrigation. In 2006, the tomatoes were sown in transplant trays in a greenhouse on 11 May, 2006 and the Blue Hubbard trap crop transplant trays were sown in the greenhouse on 18 May, 2006. The tomato and Blue Hubbard plants were transplanted into the field on 6 June, 2006 at the same time that the ‘Cobra’ slicing cucumbers were direct-seeded. In 2007, the Blue Hubbard trap crop was sown in transplant trays on 6 May, 2007 and the tomatoes and cucumbers were sown in transplant trays on 15 May, 2007 in the greenhouse. All plants were transplanted into the field on 7 June, 2007. The rows were 7.6 m-long and spaced 1.8 m apart with an in-row plant spacing of 0.5 m. The field site was planted with a rye, Secale cereale L., cover crop in the fall of 2006 and 2007 which was mowed and plowed into the soil before planting the field with cucumber and tomato, and had been in a soybean, Glycine max L., monoculture in 2003, 2004 and 2005. The student organic farm site (ca. 800 m from the organic transition plot) was a 91 m x 17 m field of assorted cucurbits planted in raised beds and drip irrigated. Rows were 1.5 m apart and in-row plant spacing was 0.8 m. This field previously contained a potato, Solanum tuberosum L., monoculture in 2005. Weeds were managed with plastic mulch at the organic transition research field site and hand hoeing at the student organic farm field site. Each site was visually scouted bi-weekly for the first appearance of striped cucumber beetles. The first detection of striped cucumber beetles at the organic transition field site was 20 June in 2006 and 27 June in 2007, and first detection was on 12 June in 2006 at the Student Organic Farm site. In both settings, striped cucumber beetle densities were measured visually by counting the total number of beetles on randomly selected plants.
Increasing levels of plant diversity to protect cucumber: In 2006 at the organic transition field site, three treatments differing in their level of plant diversity were tested for their effect on striped cucumber beetle density and plant damage. The treatments were replicated plots of cucumber alone (cucumber monoculture), cucumber with a squash trap crop, and cucumber and tomato polyculture with a squash trap crop. The cucumber monoculture plots were separated from the plots containing trap crops by a 3 m alley of bare soil. For treatments with a squash trap crop, the trap crop was placed in its own row in the center of the plot 2 m from the nearest rows. The trap crop was Blue Hubbard squash. While squash trap crops protecting cucumber are usually placed on the field perimeter, our trap crop was placed in the field interior for this study to focus on the relative attractiveness of the trap crop and cucumber crop, separating the effect of the trap crop from field edge effects. For the cucumber and tomato polyculture with a squash trap treatment replicates, two sets of four raised beds alternated with cucumbers and tomatoes. The treatments were replicated four times in a randomized complete block design (Fig. 2.1). A row of cucumbers covered with a floating row cover was also placed in each treatment to serve as a positive control. The row covers were removed once the cucumber plants began to flower (17 July in 2006 and 11 July in 2007) to allow pollinator access. This study was a subcomponent of a larger experimental plot that also explored effects of tomato planting strategies and cover crops on soil building.
Data collection: While adult beetles were active, beetles were visually counted and percent defoliation was visually estimated approximately twice per week on eight randomly selected cucumber plants in internal rows of the cucumber monoculture and cucumber with trap crop treatment replicates, four randomly selected cucumber plants on internal rows of the cucumber and tomato polyculture with trap crop treatment, four squash trap crop plants for appropriate treatments, and four cucumber plants in the rows with floating row cover by manipulating and observing the plants through the transparent row cover without removing it. Cucumbers were harvested on a weekly basis for five weeks and marketable yield was recorded. Marketable yield was based on visually assessing the damage and fruit quality and sorting the total yield into marketable and unmarketable fruit.
2007 modifications: In 2007, the experimental design remained the same except that the cucumbers were transplanted instead of direct seeded, and a foliar spray of PyGanic EC 1.4 (pyrethrum, 1.17 liters/ha, McLaughlin Gormley King Company, Minneapolis, MN), an organically certified insecticide, was applied to the Blue Hubbard trap crop. Both these changes were aimed at relieving cucumber beetle feeding pressure on the seedling cucumber plants. Spraying was triggered whenever striped cucumber beetle counts exceeded 2 per plant in the trap crop. To supplement the marketable yield data, beetle damage on fruit was measured as percent scarring per fruit for cucumber on the vine on eight randomly selected plants per replicate in all treatments.
Data analysis: A repeated measures analysis of variance (ANOVA) for a randomized complete block design was conducted using PROC MIXED (SAS Institute 2004) to compare striped cucumber beetle densities, percent defoliation and percent fruit scarring among the three plant diversity treatments across all dates of observation. All data were log (x + 1) transformed to stabilize variances and meet the assumptions of ANOVA. Based on the ANOVA, the interaction between plant diversity treatment and date was significant in both years of the study (see Results and Discussion). Therefore a post hoc ANOVA was performed for each individual sample date, and plant diversity treatments were compared using t-tests of least squares means (P < 0.05) (SAS-Institute 2004). The same procedure was also used to test plant diversity treatment differences in total marketable yield for each year, except accumulated yield was analyzed and date was not a factor in the analysis. Means and standard errors of beetle densities, defoliation, and yield data that were taken on the squash trap crop and cucumber under the row covers were also calculated as a reference for the ANOVA results comparing the plant diversity treatments. Trap crop enhancement to protect cucumber: In 2006 at the student organic farm, a 90 m-long trap crop of Blue Hubbard squash was planted along the edge of a 90 m x 17 m field of assorted cucurbits to test the potential of enhancing trap crop effectiveness by adding cucurbitacins. Beyond the Blue Hubbard squash (away from the crop) was a 90 m-long swath of unmowed grass. These paired rows were divided into five 18 m-long replicates. In each replicate, half of the trap crop and half of the grass strip was randomly assigned to be treated with an attractant while the other half was left untreated in a two by two factorial design of five replicated blocks (Fig. 2.2). The attractant was a twice weekly spray of cucurbitacin (2 liters of water mixed with 2.3 grams of powdered buffalo root per liter [Cucurbita foetidissima HBK, Cidetrak®, Trécé Incorporated, Salinas, California]). The relative attractiveness of these treatments to striped cucumber beetles was measured by counting the number of beetles twice weekly 1 day after spraying the cucurbitacin on four randomly selected plants per replicate in the Blue Hubbard squash treatments and, for one sampling date, on an equivalent ground surface area in the unmowed grass. A visual estimate of percent defoliation of the blue hubbard was also taken. Defoliation was not recorded in the unmowed grass. Beetles were also counted on four randomly selected Butternut squash, C. moschata Duchesne, plants within each of two 90 m-long rows of Butternut squash in the field. Plants in these rows were paired with the nearest treatment replicate; one row was 1.5 m from the trap crop at the edge of the field and the other was near the center of the field, 9 m from the trap crop. Data were taken bi weekly. A repeated measures analysis of variance (ANOVA) for a randomized two by two factorial design was conducted using PROC MIXED (SAS Institute 2004) to compare striped cucumber beetle densities and percent defoliation among the Blue Hubbard squash and unmowed grass treatments with and without cucurbitacin sprays, across dates of observations. A separate repeated measures (date) single factor (distance from the trap crop row) ANOVA was used to compare cucumber beetle densities and percent defoliation on the two 90 m-long rows of Butternut squash in the field. Based on the ANOVA results, a date interaction with the main treatments was significant (see Results and Discussion); therefore a post hoc ANOVA was performed as in the plant diversity experiment (SAS-Institute 2004).
Adding plant diversity in the form of a trap crop: This study found evidence that a Blue Hubbardtrap crop, Cucurbita maxima (Duchesne), can provide early season protection to a cucumber crop, Cucumis sativus L., from striped cucumber beetle, Acalymma vittatum Fabricius (Coleoptera: Chrysomelidae). The protection can break down later in the season, resulting in feeding damage to the cucumber fruits which reduces marketable yield. Ways to prolong the life and benefits of the trap crop were explored.
Cucumber in polyculture protected by a trap crop: The addition of a tomato polyculture, Solanum lycopersicum L., to the cucumber crop with a trap crop did not further reduce cucumber beetle densities on the cucumbers compared to cucumber with a trap crop alone. This evidence suggests that while increased plant diversity in the field can aid in pest control as stated in previous studies (Bach 1980), increasing the number of species may not always have an additive effect.
Addition of a cucurbitacin foliar spray: Enhancing the attractiveness of the Blue Hubbard trap crop through the addition of a cucurbitacin foliar spray occurred during some observations, but not consistently. This may simply be because the plants are already very attractive to the beetles, making it difficult to improve attraction.
Other methods of increasing the attractiveness or longevity of the trap crop may be worthy of investigation. For example, a secondary trap might disperse the stress the striped cucumber beetles placed on the trap crop. The use of a secondary trap crop that is significantly less attractive than the primary trap crop, but still more attractive than the protected crop can also serve as a buffer in case the main trap crop deteriorates or beetle numbers overflow the primary trap crop (Shelton and Badenes-Perez 2006). Insecticide can be applied to the trap crop to increase its longevity, but such applications may cause these highly mobile beetles to move elsewhere, a behavior that may have obscured treatment differences in the second year of this study.
If making the trap crop more attractive to striped cucumber beetles proves difficult, it may be better to turn efforts to trying to decrease the attractiveness of the main cucumber crop to the striped cucumber beetles.
Row covers: Floating row covers provided an excellent physical exclusion barrier against striped cucumber beetles. This finding is not new (Adams et al. 1990, Bextine et al. 2001, Mueller et al. 2006) but the comparison of its effectiveness with the other methods used in this study is striking and may provide incentive for growers who are not already using them to seriously consider floating row covers as a control method.
Overall these data provide evidence that adding plant diversity in the form of a Blue Hubbard squash trap crop can provide a cucumber crop with protection from striped cucumber beetle, particularly early in the season. But without another form of added protection to supplement the trap crop benefit in attracting beetles does not translate to improved yield. The traditional form of added protection is the use of an insecticide once beetles are detected in the trap crop (Hokkanen 1991, Javaid and Joshi 1995, Shelton and Badenes-Perez 2006). A polyculture system or spray of cucurbitacins may be more viable for organic production and more suitable for those organic producers wishing to avoid use of insecticides. Unfortunately, neither of these alternatives provided substantial addition to the attractiveness of the squash trap crop, as compared with the high level of protection provided by the row covers. The use of an organic certified insecticide the second year of our experimentation did reduce a high beetle population early in the season, confirming the advise to use insecticides once beetles are detected, but high beetle populations encountered and placement of the trap crop within the field may have prevented seeing the full value of using an insecticide to a trap crop grow on a field edge as seen by others (Hokkanen 1991, Javaid and Joshi 1995, Shelton and Badenes-Perez 2006). Given the good mobility of cucumber beetles, addition of a feeding deterrent to the protected crop along with the attractiveness of the squash trap crop may be another approach to consider (Miller and Cowles 1990) for those organic producers who wish to avoid use of insecticides and cannot use row covers due to cost or other factors.
Educational & Outreach Activities
List of Publications:
Web Page: http://www.ipm.msu.edu/noncrop/noncrop.htm
Masters Thesis: Evaluating organic-compliant management strategies for striped cucumber beetle in cucumbers.
Journal Article: A journal article is in progress, but has not yet been completed or submitted.
List of Events:
Thesis defense August 21st 2008, 9:00 am in Room 244 Natural Sciences
Presentation at the 2006 National ESA meeting
2006 and 2007 Michigan Ag Expo Presentations
Our presentation at the ESA annual meeting and presence at the 2006 and 2007 Michigan Ag Expo has allowed us to speak with growers and share some of our early findings. We have no hard data on yield increases or dollars saved per acre. The major obstacle here is that the control methods tested were found to provide little to no late season protection, allowing beetles to scar the mature fruit and reduce marketable yield even if total yield has been increased. While we have been unable to implement, test, and record a much needed method for late season organic protection of cucumbers from striped cucumber beetle, we have contributed to the body of knowledge surrounding cucumber beetle behavior and management, particularly in the early to mid growing season, and offered up potential solutions to late season protection that will require further research. Our presentations and web page have provided Michigan growers with useful and practical information regarding sustainable agricultural practices. This work is aimed at encouraging organic and sustainable agricultural practices such as cover crops and trap cropping throughout Michigan.
The methods of striped cucumber beetle control we tested on cucumbers failed to provide the strong late season protection required to prevent extensive fruit scaring. This factor has minimized any potentially beneficial economic impact that this research could otherwise have due to unacceptable reductions in marketable yield. This does, however, suggest a critical component for future research to focus on. The potential economic impact of this work in the future will hinge largely upon the ability of future research to find effective means of late season control of striped cucumber beetles.
Based on the results presented here, this study strongly supports the use of floating row covers to growers so long as they are an economically viable option for the scale of their cucumber production operation. The caveat for this control method is that the row covers must be removed once the cucumber plants begin flowering to allow pollination, and their benefits can be minimized by late season feeding damage to and subsequent scarring of the cucumber fruits. This method would be most effective when combined with some other control measure that provides protection later in the growing season after the row covers have been removed.
The use of a trap crop is also recommended based on this study’s results, but does not appear to be sufficient to provide striped cucumber beetle protection on its own. I would recommend using a Blue Hubbard trap crop in addition to row covers over the protected crop. To minimize breakdown of the Blue Hubbard trap crop later in the season, use transplants. The more time they have to grow before the beetles arrive, the better their chances are of surviving to provide protection later in the growing season. The use of a secondary trap crop may also help as a backup in case the primary trap crop fails to contain the striped cucumber beetles throughout the growing season (Shelton and Badenes-Perez 2006) and should be investigated in this system.
The trap crop effect might well be enhanced through the use of the stimulo-deterrent strategy by decreasing the attractiveness of the cucumber crop to the striped cucumber beetles with some form of deterrent (Miller and Cowles 1990). Known deterrents of striped cucumber beetles include: tetrahydropyranyl ethers (Reed and Jacobson 1983), an ethanol extract of Trewia nudiflora (Euphorbiaceae) seed (Freedman et al. 1982), an ether extract of the defatted nuts of tung, Aleurites fordii Hemsl. (Jacobson et al. 1978), the extracts of Piper spp., Piperaceae, (Scott et al. 2004 and 2008), and several botanical derivatives (Reed and Jacobson 1989). Kaolin clay dust and other particle film barriers have also been shown to have repellant effects on striped cucumber beetle feeding (Chittenden 1923).
Pesticide use is limited in an organic system, but it could prove an important tool for reducing striped cucumber beetles late in the season once the row covers have been removed, particularly if the other control measures such as the perimeter trap crop are not diverting enough of the striped cucumber beetles away from the cucumber crop’s developing fruit. Pesticide use should be limited as much as possible to reduce impacts on pollinators and other beneficial insects.
Areas needing additional study
There are a number of lines of inquiry which further research might take. Research focusing on the trap crop element of this study could look at assessing other kinds of trap crop enhancements, since it may be that other methods of adding more cucurbitacins to the Blue Hubbard trap crop or the use of other chemical attractants might prove more effective than the method tested in this study. Other potential attractants include striped cucumber beetle aggregation pheromones and cucurbit flower volatiles (Metcalf 1985, Andersen and Metcalf 1989, Smyth and Hoffman 2003, Andrews et al. 2007). Sex pheromones have been isolated for banded cucumber beetle, Diabrotica balteata LeConte (McLaughlin et al. 1991, Ventura et al. 2001), so similar pheromones may exist for striped cucumber beetles which could also be extracted and used as an attractant. Several other kairomone formulations have been found to be effective in attracting striped cucumber beetles (Jackson et al. 2005) which could likewise be tested as a trap crop enhancement.
The stimulo-deterrent method could also be used to increase the relative attractiveness of the trap crop by testing various methods of decreasing the attractiveness of the main cucumber crop, and a future study could focus on comparing various methods and techniques to that end. In this study it was difficult to determine the effects that the addition of a PyGanic spray had in the second year of the study, so future research could include such insecticide use as a treatment to better gauge its actual effectiveness in lowering striped cucumber beetle densities when applied to the trap crop. This treatment could be compared with other methods for reducing striped cucumber beetle densities on the trap crop such as the use of a bug vacuum.
Since row covers provide early season exclusion of striped cucumber beetles, future experiments could test placing row covers over the trap crop as well as the protected crop. This should deny striped cucumber beetles suitable habitat and oviposition sites in the field early in the season. This tactic could potentially prevent striped cucumber beetles from infesting the trap crop only to multiply and spill over into the protected crop as soon as the row covers are removed. By barring the cucumber beetles access to all potential host plants in the field, many of them would be forced to relocate and lay their eggs elsewhere, potentially reducing the number of beetles in the field later in the season after row cover removal. Meanwhile this tactic might save the trap crop for later use, keeping it fresh for when row covers are removed.
Finally, it would be good to correlate observations in this study and any similar field studies that may follow with an analogous laboratory study to better zero in on specific treatment effects in a more controlled environment.