- Vegetables: beans
- Pest Management: biological control, cultural control, integrated pest management
- Production Systems: organic agriculture
Our three main goals were: 1. to determine if certain beans are more susceptible to damage from Mexican bean beetle; 2. to test if beans grown on reflective, polyethylene mulches are less likely to incur damage from Mexican bean beetle; 3. to measure horticultural and ecological effects of insecticidal seed treatments in snap beans. Certain varieties were more susceptible to Mexican bean beetle than others; reflective mulches, ‘metallized’ and white, significantly reduced beetle populations and significantly increased marketable yield; and thiamethoxam seed treatments had occasional, but limited effects on insect communities and stand health in snap beans.
Snap beans are an important fresh-market crop in Virginia with more than 5,500 acres grown and one of the largest packing facilities in the U.S. located in the state. Mexican bean beetle (MBB), Epilachna varivestis Mulsant, (Coleoptera: Coccinellidae) is one of most serious pests of that crop, particularly in higher elevations in the state (Nottingham and Kuhar 2014). Mexican bean beetle causes injury by feeding on the leaves and pods of bean plants. Heavy leaf feeding reduces photosynthetic activity, and can reduce marketable pod productions (Howard 1924). Pod feeding creates unsightly damage and opening for pathogen entrance; either of which may render pods unmarketable. Although this insect can be managed with foliar sprays of insecticides, more sustainable approaches are needed to alleviate the reliance on chemical control.
Currently, the only alternative, non-chemical method for managing MBB is via inundative releases of the parasitoid wasp, Pediobius foveolatus (Crawford) (Fess 2008). Although releasing these wasps can be effective, it has some major challenges. Achieving adequate control is expensive; about $144 per acre per release, and numerous releases per season are often necessary (Stoner 2002). New releases yearly are mandatory, as this wasp species is not native to North America, and cannot survive winters in this continent (Stevens et al. 1975). Wasps are often compromised by inclement weather, such as too much rain and high or low temperatures (Stoner 2002). Also, if a grower experiences an outbreak of any other common pest, such as potato leaf hoppers or thrips, he or she can no longer use any insecticide without potentially killing these wasps. We believe that our research will provide additional options to bean growers who are interested in integrated pest management.
Our first goal was to assess resistance and susceptibly to MBB in morphologically different snap bean and lima bean varieties (objectives 1 and 2). Previous research has shown that there is very little difference in MBB susceptibility among morphologically similar green bean varieties (Fess 2008). We decided to screen morphologically different varieties: common green snap bean (‘Caprice’), yellow wax snap bean (‘Rocdor’), purple wax snap bean (‘Dragon’s Tongue’), bush lima (‘Fordhook’), pole lima (‘King of the Garden’), and dwarf bush lima (‘Henderson’). This information will help growers who experience damaging levels of MBB choose more resistant varieties, or use perferred varieties as trap crops.
We also tested a more direct method for managing MBB in snap beans. Our goals was to determine if planting beans on reflective plastic (polyethylene) mulches would reduvce damage from MBB (objective 5). Past research shows that MBB adults and larvae abscond from direct light (Howard and English 1924, Miller 1930). Also, survival at all life stages decreases as light intensity and temperature increases (Marcovitch and Stanley 1930, Miller 1930, Kitayama et al. 1970, Wilson et al. 1982, Mellors and Bassow 1983, Mellors et al. 1984). White and reflective silver (‘metalized’) plastic mulches increase light intensity and temperature near the ground, compared to bare soil (Ham et al 1993). We hypothesized that reflective plastic mulches would create less habitable environments for MBB, and therefor reduce their ability to injur the crop.
Seeds with fungicide and bactericide coatings have been common in vegetable agriculture for decades. More recently, and less frequently (especially in snap beans), insecticides are added to the seed-treatment mixture. Cruiser 5SF® (thiamethoxam), a systemic neonicotinoid, has been shown to control snap beans pests, such as bean leaf beetle, potato leaf hopper, and thrips, up to 38 days (Nault et al. 2004, Koch et al. 2005). However, insecticides can have trickle-down effects on arthropod communities as well. For instance, if an early season pest, like thrips, are killed off, predator arthropods, like minute pirate bugs and damsel bugs, may also be reduced due to lack of prey. If that is the case, secondary pest outbreaks could be more likely.
Our objective was to measure the differences in arthropod communities in plots with seed treatments and those without (objective 3). We also measured stand density, insect damage, plant health, and total pod yield in these treatments to determine all potential benefits, or lack-there-of, gained from using insecticide seed treatments in snap beans. The results of this experiment will elucidate the broader effects that treated bean seeds have on arthropod communities, as well as how beneficial seed treatments are to stand productivity in snap beans.
Ham, J., G. Kluitenberg and W. Lamont. 1993. Optical properties of plastic mulches affect the field temperature regime. Journal of American Horticultural Society 118(2): 188-193
Howard, N. F. 1924 The Mexican bean beetle in the East. USDA Agricultural Bulletin No. 1407.
Howard, N. F. and L. L. English. 1924. Studies of the Mexican bean beetle in the Southeast. USDA Agricultural Bulletin No. 1243.
Fess, T. L. 2008. Organic management of Mexican bean beetle (Epilachna varivestis) in snap bean (Phaseolus vulgaris L.). M.S. Thesis. West Virginia University, Morgantown.
Kitayama, K., R. E. Stinner, and R. L. Rabb. 1979. Effects of temperature, humidity and soybean maturity on longevity and fecundity of the adult Mexican bean beetle, Epilachna varivestis. Environmental Entomology 8(3): 458-464.
Koch, R. L., E. C. Burkness, W. D. Hutchison, T. L. Tabaey. 2005. Efficacy of systemic insecticide seed treatments for protection of early-growth-stage snap beans from bean leaf beetle (Coleoptera: Chrysomelidae) foliar feeding. Crop Protection 24: 734-742.
Marcovitch, S. and W. W. Stanley. 1930. The climatic limitations of the Mexican bean beetle. Annals of the Entomological Society of America 23(4): 666-686
Mellors, W. K. and F. E. Bassow. 1983. Temperature-dependent development of Mexican bean beetle (Coleoptera: Coccinellidae) immatures on snap bean and soybean foliage. Annals of the Entomological Society of America 76(4): 692-698.
Mellors, W. K., A. Allegro, and A. M. Wilson. 1984. Temperature dependent simulation of the effects of detrimental high temperatures on the survival of Mexican bean beetle eggs (Coleoptera: Coccinellidae). Environmental Entomology 13(1): 86-94.
Miller, D. F. 1930. The effect of temperature, relative humidity and exposure to sunlight upon the Mexican bean beetle. Journal of Economic Entomology 23: 945-955.
Nault, B. A., A. G. Taylor, M. Urwiler, T. Rabaey, W. D. Hutchison. 2004. Neonicotinoid seed treatments for managing potato leafhopper infestations in snap bean. Crop Protection 23: 147-154.
Nottingham, L. and T. Kuhar. 2014 a. History, distribution and pest status of the Mexican bean beetle. Virginia Cooperative Extension Publication ENTO-62NP.
Stevens, L. M., A. L. Steinhauer and J. R. Coulson. 1975. Suppression of Mexican bean beetle on soybeans with inoculative releases of Pediobius foveolatus. Environmental Entomology 4(6): 947-952.
Stoner, K. A. 2002. Using Pediobius foveolatus as biological control for Mexican bean beetle on organic vegetable farms. Connecticut Agricultural Experiment Station No. ENO22.
Wilson, K. G., R. E. Stinner, and R. L. Rabb. 1982. Effects of temperature, relative humidity, and host plant on larval survival of the Mexican bean beetle, Epilachna varivestis Mulsant. Environmental Entomology 11(1): 121-126.
Objective 1:(2013, 2014 and 2015) Evaluate differences in Mexican bean beetle survival, abundance and feeding injury among six bean varieties.
Objective 2:(2013 and 2014) Determine if MBB will exhibit host preference among various bean crops, using mark-release-recapture.
Objective 3:(2013, 2014 and 2015) Evaluate the effects of systemic neonicotinoid insecticides on arthropod communities in snap beans, including key pests, non-pests herbivores and beneficial arthropods.
Objective 4:(2013) Determine if delayed planting may reduce Mexican bean beetle damage in snap beans.
Objective 5:(2014 and 2015) Evaluate the utility of metalized plastic mulch to manage Mexican bean beetle populations and Increase Snap bean yields.