Organic Management of Cucumber Beetles in Cucurbits
Populations of striped cucumber beetles in watermelon were reduced by 61% in a treatment containing companion plants (radish, tansy, and nasturtium) thought to repel cucumber beetles and in a treatment including plants (buckwheat, cowpea, and sweetclover) believed to attract beneficial insects. These treatments did not affect populations of spotted cucumber beetles. Aluminum-coated plastic mulch did not affect cucumber beetle populations; however, the mulch was largely covered with vines when the cucumber beetles arrived in early July. Pawpaw extracts from 12 cultivars were toxic to brine shrimp at concentrations as low as 10 ppm, suggesting they may be effective insecticides
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
Activities for this project began in 2002. A field experiment at the KSU research farm examined individual methods of managing cucumber beetles organically in watermelon. Watermelon was used for the first year because it is not highly susceptible to bacterial wilt, which is transmitted by cucumber beetles. This assured that beetle populations could be monitored on the test crop all season. Four treatments were replicated three times in a randomized block design and included (1) an untreated control, (2) Al-coated reflective plastic mulch, (3) use of companion plants thought to repel cucumber beetles (radish, tansy, and nasturtium), and (4) use of companion plants believed to attract beneficial insects (buckwheat, cowpea, and annual sweetclover). Numbers of cucumber beetles captured on sticky traps were low until early July. Planting rows of repellent or attractant plants between watermelon rows reduced populations of striped cucumber beetles compared to the control or aluminum-coated plastic treatments on all nine weekly sampling dates in July and August. Differences were significant (P = 0.05) on two dates in August when beetle populations were relatively high. These reductions averaged 61% and ranged from 39 to 86% for the nine sampling dates. Flowering buckwheat contained populations of Pennsylvania leatherwings, (thought to be a predator of cucumber beetles) as high as 17 insects/square meter in early July. Effects of repellent and attractant plants on cucumber beetle populations were similar, suggesting that such effects may not necessarily have been caused by direct repelling or attracting of insects. It is possible that interplanting these non-cucurbit plant species between melon rows may have confused cucumber beetles and lowered their populations. Repellent and attractant plants had little effect on populations of spotted cucumber beetles, but use of repellent or attractant plants kept total populations of cucumber beetles below a suggested maximum tolerable threshold level based on sticky trap counts, whereas beetle populations in the control and Al-plastic treatments exceeded this threshold level. Aluminum-coated plastic mulch did not affect cucumber beetle populations; however, the mulch was largely covered with vines when the cucumber beetles arrived abnormally late in early July. Muskmelon will be used in years 2 and 3 to determine the most successful methods in used year 1, plus additional methods, can provide acceptable control of beetle and bacterial wilt damage in cucurbit crops highly susceptible to bacterial wilt.
Objectives 3 and 4
Twigs of 12 pawpaw selections were collected in June, and general toxicity of twig extracts containing acetogenin compounds was determined using a brine shrimp bioassay. Twig extracts from all 12 pawpaw selections were highly toxic to brine shrimp at concentrations of 10, 100, and 1000 ppm (w/v), suggesting that pawpaw extract has potential as an organic insecticide.
A comparison of two extraction methods indicated that extracts obtained using a multiple-solvent method were more toxic to brine shrimp than extracts obtained using a single-solvent method. In years two and three, the ability of pawpaw extract to kill cucumber beetles and/or act as an anti-feedant will be examined in laboratory experiments. We have been culturing cucumber beetles in the laboratory for use in such experiments. If results are successful, a field test is planned in year 3.
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. Row covers can be used to control cucumber beetles only before flowering, and 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, this project has significant national and local impact.
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.
As planned, five farmers have volunteered to do on-farm research during the 2nd year of the project to test organic methods for managing cucumber beetles. Research successes will be observed by other farmers at field days. Experimental plots at the Kentucky State University Research Farm have will be viewed by participants at monthly “Third Thursday” Sustainable Agriculture Workshops. Results from the first year of the project were disseminated to growers and scientists by the following oral presentations:
Cline, G.R. S.K. Parker, J.S. Sedlacek, and A.F. Silvernail. 2003. Research in organic control of cucumber beetles: year 1 results. Annual Meeting of Kentucky Vegetable Growers Association. Lexington, KY. January 6-7.
Cline, G.R. S. K. Parker, A. F. Silvernail, K. Kaul, R.J. Barney, A.M. Hanley, and J.D. Sedlacek. 2002. Organic management of cucumber beetles in watermelon (Citrillus lanatus). Kentucky Academy of Science Annual Meeting. Highland Heights, KY. Nov 7-9..
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.
Pettaway, V. 2003. Organic cucumber beetle control: toxicity of pawpaw extracts. Senior Student Biology Seminar. Kentucky State University. Frankfort, KY. February 28.