Organic Management of Cucumber Beetles in Cucurbits
Striped (Acalymma vittatum) and spotted (Diabrotica undecimpuncta) cucumber beetles are a major problem in the organic production of cucurbit crops including squash, cucumber, pumpkin, and melons. Larvae in the soil feed on roots, whereas adults feed on leaves, flowers, and fruit. Adult beetles also act as vectors for the transmission of Erwinia tracheiphila, which causes bacterial wilt disease in cucurbits. Bacterial wilt is the most serious disease threat to muskmelon and cucumbers in Kentucky. In 2003, organic methods for managing cucumber beetles in muskmelon (Cucumis melo) grown on plastic mulch were examined using a factorial, split-plot, randomized block experimental design. Four main plot treatments consisted of an untreated control and the use of pyrethrin insecticide, aluminum-coated plastic mulch (Al-plastic), and rows of companion plants between alternate muskmelon rows. Subplot treatments were plus or minus use of row covers. Companion plants included a combination of radish (Raphanus sativus), which is believed to repel cucumber beetles, and buckwheat (Fagopyrum esculentum), which is believed to attract beneficial insects. Muskmelon yields were significantly (P < 0.05) greater in the Al-plastic and companion plant treatments than in the control treatment, and differences were attributed to cucumber beetle damage. The highest yields were obtained using Al-mulch, and use of Al-mulch significantly (P < 0.05) increased vegetative cover compared to the control treatment. Use of lightweight row covers until flowering significantly (P < 0.05) increased melon yields. Populations of adult beetles were always lowest in the companion plant treatment. Beetle populations in the companion plant and Al-mulch treatments were consistently lower than in the control treatment, and differences were significant (P < 0.05) on four of nine sampling dates. It was concluded that use of Al-mulch, companion plants, and row covers were useful organic methods of managing cucumber beetles in muskmelon. Pawpaw trees are known to contain acetogenin compounds having insecticidal properties. In laboratory experiments,extracts of pawpaw twigs were highly toxic to brine shrimp, and there was little variation in toxicity among pawpaw selections. However, preliminary experiments indicated that pawpaw extracts were not highly toxic to striped cucumber beetles and that cucurbit leaves treated with such extracts did not greatly deter beetle feeding.
1. Compare organic methods for managing cucumber beetles in watermelon, including use of reflective mulches, beneficial insects, trap crops, cover crops, and companion plants.
2. Develop an organic system for managing cucumber beetles with muskmelon including combinations of management methods in a systems-oriented approach.
3. Determine direct and systemic toxic effects of pawpaw extracts on striped cucumber beetles.
4. Determine insecticidal effects of pawpaw extract on cucumber beetles in muskmelon.
To accomplish objectives 1, 2, and 4, field experiments are being conducted during the growing season, whereas laboratory experiments are done during the off-season to address objective 3.
Objectives 1 and 2
To accomplish Objective 2, a split- plot, factorial, randomized block experiment with muskmelon was replicated three times at the Kentucky State University Research Farm in 2003.
Main plot treatments included: (1) an untreated control, (2) use of aluminum-coated plastic mulch (Al-plastic), (3) use of buckwheat and radish companion plants, and (4) weekly spraying with pyrethrin organic insecticide. Based on results from a previous watermelon experiment (Obj. 1), radish was used to repel cucumber beetles and buckwheat was selected to attract beneficial insects. Subplot treatments were plus or minus use of row covers.
Total weight and numbers of muskmelon were highest in the Al-plastic treatment, and these yields were significantly greater (75% and 66%, respectively) than those in the control treatment. Muskmelon numbers from the companion plant treatment were significantly greater (39%) than in the control. No significant differences were detected between yields from the Al-plastic and companion plant treatments or between yields from the pyrethrin and control treatments. Use of row covers significantly increased total melon weight (47%) and melon numbers (49%).
Responses of vine cover to main plot treatments on both sample dates were generally similar to responses of muskmelon yields. Vine cover was highest using Al-plastic and significantly greater than cover in the control or pyrethrin treatments. Vine cover in the companion plant treatment was intermediate between cover in the Al-plastic and control treatments. Vine cover was significantly greater with row covers than without row covers. Treatment effects on vine cover were due to cucumber beetles as confirmed by the University of Kentucky Plant Diagnostic Laboratory.
Populations of total cucumber beetles (striped + spotted) were consistently greater in the control than in Al-plastic and companion plant treatments, and differences were significant on four of nine sample dates for both populations. This trend was less evident for spotted beetles, but differences were significant on two dates. Beetle populations obtained using Al-plastic and companion plants were not significantly different.
It was concluded that use of Al-mulch, companion plants, and row covers were effective organic methods of managing cucumber beetles in muskmelon.
These data were supported by experiments conducted on farms of Linda McMaine, Peter Cashel, and Megan Alexander. Demonstrations were observed by other farmers at the Kentucky State University Farm Field Day in September and plots were viewed by others at the farm of Linda McMaine in August.
In laboratory experiments, extracts containing acetogenin compounds were obtained from twigs of different pawpaw selections using two extraction methods. In initial experiments, brine shrimp were used to examine two extraction methods and investigate differences in extract toxicity among different pawpaw selections. Extracts obtained using the more rigorous method were toxic to brine shrimp and were more toxic than extracts obtained using the other method.
Extracts obtained using the more rigorous method at concentrations of 1000 mg/l (w/v) were generally completely lethal to shrimp, whereas 20% and 40% of shrimp survived at extract concentrations of 100 and 10 mg/l, respectively. There was little variation in toxicity to shrimp among extracts obtained from different pawpaw selections.
In initial experiments, pawpaw twig extracts at concentrations of 5000 g/l were not toxic to striped cucumber beetles when beetles were directly treated with extract. Also, treatment of leaves with such extracts did not greatly deter beetles from feeding on leaves when leaves were treated with extract.
Impacts and Contributions/Outcomes
Striped and spotted cucumber beetles are important insect pests in the production of cucurbits because they feed on these plants and act as vectors of the pathogen which causes bacterial wilt disease. Current organic insecticides for cucumber beetles (e.g., rotenone, pyrethrins) are highly toxic to humans and/or easily degraded by sunlight. Cucumber beetles were the most important organic vegetable insect pest identified in a national survey and in a survey conducted in Kentucky by the authors in a SARE planning project. Thus, cucumber beetles are an important national and local problem. Organic vegetable production is especially appealing to small farmers. Improvement of organic management methods for cucumber beetles would make organic production of cucurbits more profitable for small farmers and help to preserve small farms. Also, such improvements should reduce use of inorganic insecticides, which are potential environmental pollutants and health hazards. Results from 2003 indicated that use of row covers, companion plants, and Al-coated plastic significantly increased organic muskmelon yields through management of cucumber beetles. Thus, adaptation of these methods by organic growers has national and local impact.
Three farmers participated in on-farm research during 2003, which tested organic methods for managing cucumber beetles. Experimental plots in the large field experiment at the Kentucky State University Research Farm viewed by participants at monthly “Third Thursday” Sustainable Agriculture Workshops and at the KSU Farm Field Day. On-farm research plots were viewed by other farmers. Results from the project were disseminated to growers and scientists by the following presentations:
Cline, G.R. S.K. Parker, J.S. Sedlacek, and A.F. Silvernail. 2003. Research in organic control of cucumber beetles. Annual Meeting of Kentucky Vegetable Growers Association. Lexington, KY. January 6-7, 2003.
Pettaway, V. 2003. Organic cucumber beetle control: toxicity of pawpaw extracts. Senior Student Biology Seminar. Kentucky State University. Frankfort, KY. February 28, 2003.
Pettaway, V., S.K. Parker, G.R. Cline, and K.W. Pomper. 2003. Organic cucumber beetle control: preliminary experiments examining toxicity of pawpaw extracts to brine shrimp. Association of Research Directors Annual Symposium. Atlanta GA. March 29-April 2, 2003.
Cline, G.R., K. Kaul, and A.F. Silvernail. 2003. Organic management of cucumber beetles in muskmelon (Cucumus melo). Kentucky Academy of Science Annual Meeting. Highland Heights, KY. Nov 6-8, 2003.