Management of Mexican Bean Beetle, Epilachna varivestis Mulsant, in Snap Beans Using Cultural Control Strategies

Final Report for GS13-120

Project Type: Graduate Student
Funds awarded in 2013: $10,622.00
Projected End Date: 12/31/2015
Grant Recipient: Virginia Tech
Region: Southern
State: Virginia
Graduate Student:
Major Professor:
Dr. Thomas Kuhar
Virginia Tech
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Project Information

Summary:

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.

Introduction

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.

 

References:

 

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.

Project Objectives:

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.

 


Cooperators

Click linked name(s) to expand
  • Louis Nottingham

Research

Materials and methods:

Objective 1:

(2013, 2014 and 2015) Evaluate differences in Mexican bean beetle survival, abundance and feeding injury among six bean varieties.

 

2013 Methods:

  • Planting Date: May 3
  • Location: Kentland Farm, Blacksburg, VA
  • Weed Mgmt:

    • Pre-emergent applied after planting: Sandea 75DF 1oz./ac. + Dual Magnum 1.5 pts./ac.
    • Mechanical weed cultivation as needed.

  • Treatments:

  1. ‘Caprice’: Green, bush snap bean. Phaseolus vulgaris
  2. ‘Rocdor’: Yellow wax, bush snap bean. Phaseolus vulgaris
  3. ‘Dragon’s Tongue’: Purple Dutch wax, bush snap bean. Phaseolus vulgaris
  4. ‘Fordhook 242’: Bush lima bean. Phaseolus lunatus.

  • Experimental Design:
  • Generalized, randomized complete block design
  • Four “plots” (blocks); >80m separation between plots.
  • Two replicates of each treatment per plot (8 replicates of each treatment; 32 replicates total).
  • Replicate size was 6.1m x 6.1m and consisted of four rows.
  • 5m spacing between replicates
  • 5m spacing between rows.
  • Data Collection

  1. MBB Sampling:

  • Sampling occurred every Monday and Friday from 6/10/13 (date after first MBB sighting) to 7/19/2013. Every replicate was sampled on sampling days.
  • 10 plants per replicate were searched, documenting numbers of MBB life stages: adults, eggs, egg masses, early instars (< 3mm long), late instars (> 3mm long), and pupae.
  • All data were normalized using a square-root transformation.
  • Data were analyzed using JMP Pro 11. ANOVA was used to detect treatment differences. Student’s t-test was used to separate means. If data could not be normalized, Wilcoxon Each pair test was used to seperate means.

  1. Stand and Pod damage:

  • Stand counts were conducted on 5/31, when plants reached first trifoliate stage. All plants in all replicates were counted
  • When snap beans were at maturity, 100 pods from each replicate were arbitrarily selected and rate as either damaged (>1 cm long damage area) or undamaged (
  • Data were analyzed using JMP Pro 11. ANOVA was used to detect treatment differences. Student’s t-test was used to separate means.

 

2014 methods:

  • Planting Date: May 11
  • Location: Kentland Farm, Blacksburg, VA
  • Weed Mgmt:

    • Pre-emergent applied after planting: Sandea 75DF 1oz./ac. + Dual Magnum 1.5 pts./ac.
    • Mechanical weed cultivation as needed.

  • Treatments:

  1. ‘Caprice’: Green, bush snap bean. Phaseolus vulgaris.
  2. ‘Rocdor’: Yellow wax, bush snap bean. Phaseolus vulgaris.
  3. ‘Dragon’s Tongue’: Purple Dutch wax, bush snap bean. Phaseolus vulgaris.
  4. ‘Fordhook 242’: Bush lima bean. Phaseolus lunatus.
  5. ‘Kind of the Garden: Pole lima bean. Phaseolus lunatus.
  6. ‘Henderson’: Dwarf, bush lima bean. Phaseolus lunatus.

  • Initial planting of Henderson beans failed to germinate. These replicates were replants two weeks later.  Though the second planting was successful, Henderson plants remained smaller than other treatments.  
  • Experimental Design:
  • Randomized complete block design
  • Four “plots” (blocks); >80m separation between plots.
  • One replicate of each treatment per plot (4 replicates of each treatment; 24 replicates total).
  • Replicate size was 6.1m x 10 m and consisted of four rows.
  • 5m spacing between replicates
  • 5m spacing between rows.

 

  • Data Collection:

  1. MBB Sampling:

  • Sampling occurred once a week from 6/9/14 (date after first MBB siting) to 7/7/2013. Every replicate was sampled on sampling days.
  • 20 plants per replicate were searched, documenting numbers of MBB life stages: adults, eggs, egg masses, early instars (< 3mm), late instars (> 3mm), and pupae.
  • A separated sample of 15 plants per replicate was conducted every week to document predator arthropods.
  • All data were normalized using a square-root transformation.
  • Data were analyzed using JMP Pro 11. ANOVA was used to detect treatment differences. Student’s t-test was used to separate means. If data could not be normalized, Wilcoxon Each pair test was used to seperate means.

  1. Pod damage:

  • When snap beans were at maturity, 100 pods from each replicate were arbitrarily selected and rated as either damaged (>1 cm long damage area) or undamaged (
  • Data were analyzed using JMP Pro 11. ANOVA was used to detect treatment differences. Student’s t-test was used to separate means.

2015 methods:

  • Planting Date: May 11
  • Location: Kentland Farm, Blacksburg, VA
  • Weed Mgmt:

    • Pre-emergent applied after planting: Sandea 75DF 1oz./ac. + Dual Magnum 1.5 pts./ac.
    • Mechanical weed cultivation as needed.

  • Treatments:

  1. ‘Caprice’: Green, bush snap bean. Phaseolus vulgaris.
  2. ‘Rocdor’: Yellow wax, bush snap bean. Phaseolus vulgaris.
  3. ‘Dragon’s Tongue’: Purple Dutch wax, bush snap bean. Phaseolus vulgaris.
  4. ‘Fordhook 242’: Bush lima bean. Phaseolus lunatus.
  5. ‘Kind of the Garden: Pole lima bean. Phaseolus lunatus.
  6. ‘Henderson’: Dwarf, bush lima bean. Phaseolus lunatus.
  7. ‘Milta’: Tepary bean. Phaseolus acutifolius
  8. ‘Hutchison’: Soybean. Glycine Max

  • Experimental Design:
  • Generalized, Randomized complete block design
  • Two “plots” (blocks); >50m separation between plots.
  • 4 replicates of each treatment per plot (8 replicates of each treatment; 64 replicates total).
  • Replicate size was 6.1m x 4 m and consisted of two rows.
  • 5m spacing between replicates
  • 5m spacing between rows.

 

  • Data Collection:

  1. MBB Sampling:

  • Sampling occurred on three dates from 6/25/15, 7/6/2015, and 7/14/2015.
  • 10 plants per replicate were searched, documenting numbers of MBB life stages: adults, eggs, egg masses, early instars (< 3mm), late instars (> 3mm), and pupae.
  • All data were normalized using a square-root transformation.
  • Data were analyzed using JMP Pro 11. ANOVA was used to detect treatment differences. Student’s t-test was used to separate means. If data could not be normalized, Wilcoxon Each pair test was used to seperate means.

  1. Plant injury:

  • Plants were assessed for foliar feeding injury by MBB on 6/23/15 (pre-flowering) and 7/2/15 (flowering)
  • Plants were rated on a 0-5 scale based on the level of injury sustained to leaves (0 being the least injury, 5 being the most).
  • Average rating per replicate were calculated and analyzed in JMP 11. Differences in injury among treatments were detected using ANOVA.  Means separation was performed using Student’s t test.

  1. Pod damage:

  • When snap beans were at maturity, 50 pods from each replicate were arbitrarily selected and rated as either damaged (>1 cm long damage area) or undamaged (
  • Data were analyzed using JMP Pro 11. ANOVA was used to detect treatment differences. Student’s t-test was used to separate means.

 

Objective 2:

(2013 and 2014) Determine if MBB will exhibit host preference among various bean crops, using mark-release-recapture.

 

2013 methods:

  • Planting Date: 8/16/13
  • Location: Kentland Farm, Blacksburg, VA
  • Weed Mgmt:

    • Mechanical weed cultivation as needed.

  • Treatments:

  1. ‘Caprice’: Green, bush snap bean. Phaseolus vulgaris
  2. ‘Rocdor’: Yellow wax, bush snap bean. Phaseolus vulgaris
  3. ‘Dragon’s Tongue’: Purple Dutch wax, bush snap bean. Phaseolus vulgaris
  4. ‘Fordhook 242’: bush lima bean. Phaseolus lunatus.
  5. ‘Hutchison’: Soybean. Glycine max

  • Mark-recapture plot design (Figure 1):
  • Two experimental plots with 5 bean varieties were planted on 8/16/13.
  • One plot was covered by a 2.5 x 3.7 x3.7m mesh cage with a steel frame; the other plot was exposed. Plots were separated by >50m.
  • Five replicates of each variety were planted in a 5×5 Latin square.
  • Each replicate contained nine plants and occupied a 60x60cm area.
  • MBB marking and release:
  • MBB adults were collected from an unused variety of snap beans, ‘Provider’ at Kentland farm on August 25th, 2013. Females were identified in the lab, for use in this experiment.
  • Using a Sharpie, oil-based paint pen, each female was marked by painting the right elytron (head facing up) with one of five colors: white, blue, green, yellow, or purple.
  • After being marked, beetles were randomly allocated to cages, where they were allowed to forage in a mixture of snap, lima and soybeans.
  • On 9/11/13, 30 healthy, feeding beetles of each color of were removed from cages and placed in a plastic containers with screen lids.

    • 6 beetles of the same color per container.

  • Beetles remained in these containers for 24 hours without food, but with a piece of water soaked floral foam.
  • On 9/12/13, 5 beetles of each color were randomly assigned to individual Petri dishes (extras were placed in a separate container).
  • Beetles were taken to field plots and released at approximately 10am, with one Petri dish released into each replicate.
  • The variety in which beetles were released was based on their mark color (white: soy; blue: ‘Fordhook’; green: ‘Caprice’; yellow: ‘Rocdor’; purple: ‘Dragon’s Tongue’).
  • Beetles were released into the canopy of a single plant in the center of the replicate. Beetles were watched until they began feeding (about 30-45 seconds). 

    • Occasionally, beetles immediately flew off the plants. These beetle were retrieved and replaced on the plant, or, if they could not be retrieved because they left the plot, they were replaced with individuals from the container of extra beetles.    

  • Sampling and analysis:
  • Plots were sampled at 24h (9/13), 72h (9/15), 120h (9/17) and 168h (9/19) after release.
  • All plants in each replicate were visually searched for MBB, documenting the color of each beetle found. Each replicate was sampled for 2 minutes.
  • Beetles were not removed from plots. Beetles recaptured at 24h, were given a second mark on the left elytron to indicate which plot they were found on that day.
  • Only marked beetles were documented.
  • Samples were analyzed four ways.

    • “Emigrated”: Number of beetles recaptured with a variety that were not originally released in that variety.
    • “Non-immigrating”: Number of beetles recaptured within a variety that were originally released in that variety.
    • “Total”: All marked beetles recaptured within a variety
    • “Immigrated vs. remained”: Percent that were recaptured in their variety of original release vs. the percent that left their variety of original release.  Percent is out of the total number of beetles recaptured from each variety of release.

  • Anova was used to detect model significance. Means separation using Tukey’s HSC.

 

2014 methods:

  • Logistics
  • Planting Date: 7/27/14
  • Location: Kentland Farm, Blacksburg, VA
  • Weed Mgmt:

    • Mechanical weed cultivation as needed.

  • Treatments:

  1. ‘Caprice’: Green, bush snap bean. Phaseolus vulgaris
  2. ‘Rocdor’: Yellow wax, bush snap bean. Phaseolus vulgaris
  3. ‘Dragon’s Tongue’: Purple Dutch wax, bush snap bean. Phaseolus vulgaris
  4. ‘Fordhook 242’: bush lima bean. Phaseolus lunatus.
  5. Bush Soybean. Glycine max

  • Plot design (Figure 1):
  • (SAME DESIGN AS 2013)
  • MBB marking and release:
  • ALL METHODS REMAINED THE SAME AS 2013, except the following changes and dates:
  • Due to the rapidly cooling season, MBB pupae and adults were collected (instead of larvae and pupae).
  • Beetles were released on 8/27/14.
  • Sampling and analysis:
  • Plots were sampled at 24h (8/28), 72h (8/30), 120h (9/1) and 168h (9/3) after release.

 

 

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.

 

2013 methods:

  • Planting Dates: Early experiment: May 3. Late experiment: July 14
  • Variety: ‘Caprice’. Bush snap bean. Phaseolus vulgaris.
  • Location: Kentland Farm, Blacksburg, VA
  • Weed Mgmt:

    • Pre-emergent applied after planting: Sandea 75DF 1oz./ac. + Dual Magnum 1.5 pts./ac.
    • Mechanical weed cultivation as needed.

  • Treatments:

  1. Treated seeds

  • Captan 400 [Captan: N-trichloromethylthio-4-cyclohexene-1,2-dicarboximide] (Fungi)
  • AG- Streptomycin [Streptomycin Sulfate: 5-(2,4-diguanidino-3,5,6-trihydroxy-cyclohexoxy)- 4-[4,5-dihydroxy-6-(hydroxymethyl)-3-methylamino-tetrahydropyran-2yl]oxy-3-hydroxy-2-methyl-tetrahydrofuran-3-carbaldehyde] (Fungi, bacteria, algae)
  • Alligiance FL [Metalaxyl: N-(2,6-dimethylphenyl)-N-(methoxyacetyl)alanine methyl este] (fungi, oomycetes)
  • Thiram [Tetramethylthiuram disulfide: dimethylcarbamothioylsulfanyl N,N-dimethylcarbamodithioate] (fungi, mammals)
  • Cruiser 5SF [thiamethoxam, 3-[(2-Chloro-1,3-thiazol-5-yl)methyl]-5-methyl-N-nitro-1,3,5-oxadiazinan-4-imine]. (Broad spectrum systemic insecticide)

  1. Untreated seeds

  • No chemical treatment
  • Experimental Design (Figure 1):
  • Generalized, randomized complete block design
  • Four identical “plots” (blocks); >80m separation between plots.
  • Four replicates of each treatment per plot (16 replicates of each treatment; 32 replicates total).
  • 5m of fallow ground separating replicates
  • Replicate size was 6.1m x 6.1m and consisted of four rows.
  • .5m of fallow ground separating rows

 

  • Data Collection

  1. Insect Sampling:

  • Insect sampling was conducted from June 10 to July 12 for the early experiment, and August 2 through September 6 for the late experiment.
  • Plots were sampled on Mondays and Thursdays each week.
  • 10 plants in each replicate were arbitrarily selected, and visually searched for all insects.

    • One leaf was selected from the base, middle and top of each plant and searched for Potato leafhopper (PLH) nymphs. Only nymphs were counted
    • Mexican bean beetles (MBB) were identified to life stage: eggs, early instars (3mm long), pupae and adults.
    • Specific life-stages of all other insects were not documented.

  • All data was transformed using a square-root transformation.
  • Data were analyzed using JMP Pro 11. ANOVA was used to detect treatment differences. Student’s t-test was used to seperate means. If data could not be normalized, Wilcoxon Each pair test was used to seperate means.

  1. Crop Quality

  • Stand counts:
  • First trifoliate count: All plants per replicate were counted once plants reached first-trifoliate stage: early experiment: 5/31; late experiment: 8/5.
  • Harvest count: Two, 1m sections of row were sampled from each replicate at pod maturity: early experiment: 7/12; late experiment: 9/16.
  • Data were analyzed using JMP Pro 11. ANOVA was used to detect treatment differences.
  • Yield:
  • All bean pods were harvested from plants sampled in the harvest stand counts.
  • All pods were weighed in grams.
  • Average pod weights per treatment and per plant were calculated.
  • Data were analyzed using JMP Pro 11. ANOVA was used to detect treatment differences.
  • Pod Damage:
  • 100 pods were arbitrarily selected from each replicate and rated as either damaged (>1 cm long damage area) or undamaged (
  • Proportion of damaged to undamaged pods was calculated and transformed using an arcsine square-root transformation.
  • Data were analyzed using JMP Pro 11. ANOVA was used to detect treatment differences.

 

2014 methods:

  • Planting Date: May 16
  • Variety: ‘Caprice’. Bush snap been
  • Location: Kentland Farm, Blacksburg, VA
  • Treatments: Original two treatments remained the same (see 2013 Methods), but an extra treatment was added. The added treatment had the same chemical mixture as the treated seed from 2013, but without Cruiser 5SF. Treatments will be referred to as UT (Untreated control), FG (Fungicide treated without Cruiser 5SF), and CFT (Cruiser 5SF + fungicide treated).
  • Experimental Design (Figure 17):
  • Generalized, randomized complete block design by layout; however, most sampling only used one replicate per plot. In such cases, data was analyzed as a randomized complete block design.
  • Four identical “plots” (blocks); >80m separation between plots.
  • Two replicates of each treatment per plot (8 replicates of each treatment; 24 replicates total).
  • 5m of fallow ground separating replicates
  • Replicate size was 6.1m x 12.2m and consisted of eight rows.
  • 5m of fallow ground separating rows
  • One replicate of each treatment per plot was reserved for vacuum sampling, and one was used for visual counts and leaf collection for thrips.

    • One pitfall trap were set in each replicate.

 

  • Data Collection

  1. Visual Count Insect Sampling:

  • Visual insect sampling was conducted from June 10 to July 8.
  • Plots were sampled on Tuesdays of each week.
  • 20 plants per replicate were arbitrarily selected, and visually searched for all insects.

    • One leaf was selected from the base, middle and top of each plant and searched for PLH nymphs. Only nymphs were counted.
    • Mexican bean beetles were identified to life stage: eggs, early instars (3mm long), pupae and adults.
    • Specific life-stages of all other insects were not documented.

  • All data was transformed using a square-root transformation.
  • Data were analyzed using JMP Pro 11. ANOVA was used to detect treatment differences. Student’s t-test was used to seperate means. If data could not be normalized, Wilcoxon Each pair test was used to seperate means.

  1. Vacuum Suction Insect Sampling

  • Vacuum samples were conducted from June 19 to July 9 to gain addition data on foliar insects, especially small predators like Minute pirate bugs.
  • A handheld, Stihl reverse leaf blower was used to suck insects within the bean canopy into 50 x 30cm mesh bags.
  • Plots were sampled on Friday each week.
  • Two rows were arbitrarily selected each week for sampling. Half of each row (3m) was vacuumed. About 2 seconds was spent vacuuming each plant.
  • Bags were taken back to the lab and put in the freezer.
  • All insects except MBB were counted. Life stages were not documented.
  • Data were analyzed using JMP Pro 11. ANOVA was used to detect treatment differences. Student’s t-test was used to seperate means. If data could not be normalized, Wilcoxon Each pair test was used to seperate means.

  1. Pitfall Trap Insect Sampling

  • In each replicate, one pitfall trap was buried in between two rows to better sample spiders, centipedes and ground beetles (Carabidae).
  • To determine placement of each trap, each between-row was given a number. A piece of paper with each between-row number was put into a hat. For each replicate, a number was drawn. 

    • Traps were always placed in the center of the between-row.

  • 5cm cups were buried in soil, with the rim about 3 cm above the soil line. Soil was filled around the cup and flush with the rim. This created a mound, which prevented water from rushing into the traps during heavy rains. 
  • About 4oz of soap water was put in the bottom of each cup to prevent arthropod from escaping.
  • Two pieces of 30cm long metal flashing were buried on opposing sides of cups to direct ground arthropods in.
  • Pitfalls traps were set on Monday and collected on the following Thursday each week.
  • Arthropods were retrieved from traps in the field, and brought back to the lab for identification.
  • All insects except MBB were counted. Life stage was not documented.
  • Data were analyzed using JMP Pro 11. ANOVA was used to detect treatment differences. Student’s t-test was used to seperate means. If data could not be normalized, Wilcoxon Each pair test was used to seperate means.

  1. Crop Quality

  • Stand counts:
  • Early: All plants per replicate were counted at first trifoliate stage: 6/11.
  • Harvest: Two, 3m sections of row were selected from each replicate at maturity: 7/14. All plants were counted.
  • Data were analyzed using JMP Pro 11. ANOVA was used to detect treatment differences. Student’s t-test was used to seperate means. 
  • Yield:
  • All pods from plants selected for the harvest stand count were removed and weighed. Average pod weights per treatment and per plant were calculated.
  • Data were analyzed using JMP Pro 11. ANOVA was used to detect treatment differences. Student’s t-test was used to seperate means. 
  • Pod Damage:
  • 100 pods were arbitrarily selected from each replicate and rated as either damaged (>1 cm long damage area) or undamaged (
  • Proportion of damaged to undamaged pods was calculated and transformed using an arcsine square-root transformation.
  • Data were analyzed using JMP Pro 11. ANOVA was used to detect treatment differences. Student’s t-test was used to seperate means. 

2015 methods:

  • Planting Dates: 5/18/2015
  • Variety: ‘Caprice’. Bush snap bean. Phaseolus vulgaris.
  • Location: Kentland Farm, Blacksburg, VA
  • Weed Mgmt:

    • Pre-emergent applied after planting: Sandea 75DF 1oz./ac. + Dual Magnum 1.5 pts./ac.
    • Mechanical weed cultivation as needed.

  • Treatments:
  • Same as 2014
  • Experimental Design (Figure 1):
  • Generalized, randomized complete block design
  • 2 blocks
  • Four replicates of each treatment per block (8 replicates of each treatment; 24 replicates total).
  • 5m of fallow ground separating replicates
  • Replicate size was 6.1m x 12m and consisted of 8 rows.
  • .5m of fallow ground separating treatment plots

 

  • Data Collection

  1. Insect Sampling:

  • Visual insect sampling was conducted weekly from 6/4 to 7/10.
  • Vacuum sampling (same method as 2014) was performed on 6/16, 7/2/ and 7/10 for to gain addition data on foliar insects, especially small predators like Minute pirate bugs (Anthocoridae).
  • Pitfall traps were set and checked weekly from 5/26/15 through 7/13/15 to better sample spiders, centepedes and ground beetles (Carabidae).
  • 10 plants in each replicate were arbitrarily selected, and visually searched for all insects.

    • One leaf was selected from the base, middle and top of each plant and searched for Potato leafhopper (PLH) nymphs and thrips.
    • Mexican bean beetles (MBB) were identified to life stage: eggs, early instars (3mm long), pupae and adults.
    • Specific life-stages of all other insects were not documented.

  • All data was transformed using a square-root transformation.
  • Data were analyzed using JMP Pro 11. For normal data, ANOVA was used to detect treatment differences and Student’s t-test was used for mean separation.  Non parametric, Wilcoxon tests were used if data could not be normalized.

  1. Crop Quality

  • Flowering stage stand count: All plants per plot were counted on 6/16/2015.
  • Data were analyzed using JMP Pro 11. ANOVA was used to detect treatment differences.
  • Yield:
  • Two, 1m sections of row were sampled from each replicate at pod maturity
  • All bean pods were harvested from plants sampled in the harvest stand counts.
  • All pods were weighed in grams.
  • Average pod weights per treatment and per plant were calculated.
  • Data were analyzed using JMP Pro 11. ANOVA was used to detect treatment differences. Student’s t-test was used for mean separation.
  • Pod Damage:
  • 100 pods were arbitrarily selected from each replicate and rated as either damaged (>1 cm long damage area) or undamaged (
  • Proportion of damaged to undamaged pods was calculated and transformed using an arcsine square-root transformation.
  • Data were analyzed using JMP Pro 11. ANOVA was used to detect treatment differences. Student’s t-test was used for mean separation.
  • Plant health:
  • Plant health was measured using a Greenseeker® handheld crop sensor to measure plant biomass via NDVI (Normalized Difference Vegetation Index) values.
  • Readings were taken from each row in all plots.
  • Average readings were analyzed using JMP Pro 11. ANOVA was used to detect treatment differences. Student’s t-test was used for mean separation.

 

 

Objective 4:

(2013) Determine if delayed planting may reduce Mexican bean beetle damage in snap beans.

               (see methods for 2013 Seed Treatment experiment, Objective 3)

 

 

Objective 5:

(2014 and 2015) Evaluate the utility of metalized plastic mulch to manage Mexican bean beetle populations and Increase Snap bean yields.

 

2014 methods:

  • Planting Date: 6/17/14
  • Location: Kentland Farm, Blacksburg, VA
  • Variety: ‘Dragon’s Tongue’. Bush, wax snap bean. Phaseolus vulgaris.
  • Weed Mgmt:

    • Pre-emergent applied after planting: Sandea 75DF 1oz./ac. + Dual Magnum 1.5 pts./ac.
    • Mechanical weed cultivation as needed.

  • Treatments:

  1. Bare soil
  2. Black plastic mulch
  3. White plastic mulch (white with black backing)
  4. Metalized plastic mulch (reflective with black backing)

  • Experimental Design (Figure 1):
  • Randomized complete block design
  • Four “plots” (blocks); >80m separation between plots.
  • One replicate of each treatment per plot (4 replicates of each treatment; 16 replicates total).
  • Individual replicates were one row of 20 bean clusters planted on plastic mulch or bare soil.

    • Clusters were 5 bean plants spaced 30cm apart.
    • Planted from seed in the field.

  • Each mulch replicate used one, 1.2 x 8.6m sheet of plastic (.9 x 8m visible).

    • Mulch furrows were cut mechanically
    • Mulch was then buried by hand.

  • Plants were watered by hand once a week
  • Data collection:

  1. MBB sampling and analysis:

  • 10 plant clusters were visually searched once a week from 7/9/14 to 8/7/14.
  • All life stages of Mexican bean beetle were documented.
  • Data were square-root transformed.
  • Differences in MBB abundance among treatments were detected using ANOVA. Student’s t-test was used to seperate means. If data could not be normalized, Wilcoxon Each pair test was used to seperate means.

  1. Predator sampling and analysis:

  • All predators observed while performing MBB counts were document.
  • Data were square-root transformed.
  • Differences in predator groups among treatments were detected using ANOVA. Student’s t-test was used to seperate means. If data could not be normalized, Wilcoxon Each pair test was used to seperate means.

  1. Yield:

  • All pods were harvested from each replicate and weighed on 8/15/14.
  • Differences in pod weight among treatments were detected using ANOVA. Means separation was performed using Student’s t test.

 

2015 methods:

  • Planting Date: 5/18/14
  • Location: Kentland Farm, Blacksburg, VA
  • Weed Mgmt:

    • Pre-emergent applied after planting: Sandea 75DF 1oz./ac. + Dual Magnum 1.5 pts./ac.
    • Mechanical weed cultivation as needed.

  • Variety: ‘Dragon’s Tongue’. Bush, wax snap bean. Phaseolus vulgaris.
  • Treatments:

  1. Bare soil
  2. Black plastic mulch
  3. White plastic mulch (white with black backing)
  4. Metalized plastic mulch (silver with black backing)

  • Experimental Design (Figure 1):
  • Generalized, randomized complete block design
  • One bed, three blocks, and 9 replicated plots of each treatment (3 per block)
  • Each treatment plot was two parallel rows of beans (3 m long, 2 meter apart) planted on one of the 4 treatments.
  • Each mulch replicate used one, 1.2 x 3.5m sheet of plastic (.9 x 3m visible).

    • Mulch furrows were cut mechanically
    • Mulch was then buried by hand.

  • Beans seeds sown in field in clusters of two. One cluster planted every .5m within plot rows. 
  • Plants were watered via a drip irrigation line. Plants were watered two days each week, for 3 hours each day.

 

  • Data collection:

  1. Light sensors:

    • Four pyranometers were used to monitor light intensity, in PAR µmol/m²s, on each treatment.
    • Each pyranometer was mounted to a metal stake, 7 inches above the surface (plastic or bare ground), facing the ground.
    • Pyranometers took one reading every 10 minutes for the duration of the experiment.
    • Pryanometers were relocated every week to reduce bias from mounting inconsistency.

  2. MBB sampling and analysis:

  • Plants were visually searched once a week from 6/11/15 to 7/8/15.

    • Five clusters arbitrarily selected and searched each week

  • All life stages of Mexican bean beetle were documented.
  • Data did not respond to transformation, nonparametric methods were used for analysis.
  • Differences in MBB abundance among treatments were detected using Wilcoxon test. Means separation was performed using Wilconxon each pair test.

  1. Predator sampling and analysis:

  • All predators observed while performing MBB counts were document.
  • Data were square-root transformed.
  • Differences in predator groups among treatments were detected using ANOVA. Student’s t-test was used to seperate means. If data could not be normalized, Wilcoxon Each pair test was used to seperate means.

  1. MBB injury

  • All plant clusters in the experiment were assessed for foliar injury on a 0-5 scale (same as 2015 variety experiment, objective 1).
  • Average rating per replicate were calculated and analyzed in JMP 11. Differences in injury among treatments were detected using ANOVA.  Means separation was performed using Student’s t test.

  1. Pod damage

  • When snap beans were at maturity, 50 pods from each replicate were arbitrarily selected and rated as either damaged (>1 cm long damage area) or undamaged (
  • Data were analyzed using JMP Pro 11. ANOVA was used to detect treatment differences. Student’s t-test was used to separate means.

  1. Yield:

  • All pods were harvested from each replicate and weighed on 7/21/15.
  • Differences in pod weight among treatments were detected using ANOVA. Means separation was performed using Student’s t test.

 

  • Lettuce Double Crop:
  • On August 1, after snap beans plants were removed, a second crop of green leaf lettuce was planted on plot of this experiment.
  • In each plot replicate, 10 lettuce transplants were planted per row.
  • Plants were harvested and weighed on 9/16/15.
  • Differences in plant weight among treatments were detected using ANOVA. Means separation was performed using Student’s t test.

Research results and discussion:

Objective 1:

(2013, 2014 and 2015) Evaluate differences in Mexican bean beetle survival, abundance and feeding injury among six bean varieties.

 

2013 Results:

               Insect Counts: In 2013, differences in MBB development were observed among varieties.  Numbers of eggs deposited on all snap bean varieties and the lima bean variety remained the same until the final two samples (Figure 1).  However, numbers of late instars found in these varieties was different among certain varieties starting 7/5/15 until the final sample.   The lima variety, ‘Fordhook’, exhibited significantly lowest number of late instars in these samples.  The purple wax variety, ‘Dragon’s Tongue’, followed by, the yellow wax variety ‘Rocdor’ and the green variety ‘Caprice’, respectively, had the most late instars.  These results show that MBB larval survival was highest on Dragon’s Tongue, followed by Rocdor, Caprice and Fordhook, respectively.  These data suggests that Dragon’s Tongue is particularly susceptible to MBB, while Caprice is more resistant in comparison (Rocdor lands in between the two).  Our lima bean control was exhibited the highest level of resistance to MBB development.

*Adult numbers were not different, and considered less accurate due to adults high mobility.  We believe eggs counts are actually a better representation of adult presence.

               Pod Damage:  No differences were observed in the number of damaged pods snap bean varieties.

 

2014 Results:

               Insect Counts:  A similar trend was observed in 2014 to 2013.  Reduced survival from egg to late larvae was observed in all lima bean varieties compared to snap beans (Figures 3 and 4).  One interesting difference was the significantly lower number of eggs found in Caprice beans than other snap beans varieties.  However, the number of late larvae found in caprice was lower different than the numbers found in other varieties, suggesting that survival on Caprice was as good or better than other varieties.   *Henderson snap beans suffered from low germination and very weak stands; so these numbers were deemed unreliable.

               Pod Damage:  No differences were observed in the number of damaged pods snap bean varieties.

 

2015 Results:

               Insect Counts:  Insect counts from this season were less cogent than past seasons.  Lima bean varieties still showed equal attractively for oviposition, with lower overall survival compared to snap beans.  However, larval survival in King of the Garden was suspiciously high, and may indicate that it is a more susceptible variety of lima bean.    In terms of snap beans what may be most important this that this was the third season that ‘Dragon’s Tongue’ exhibited the highest numbers of late larvae among all sample dates and varieties; again, suggesting that this is the most susceptible variety. Tepary bean, ‘Milta’, had low overall survival from egg to larvae.  Soybeans were rarely colonized by MBB at all.  (Figure 5 and 6)

Pod Damage:  Dragon’s Tongue experienced significantly more damage to pods from MBB than Rocdor and Carpice.  Rocdor also experienced significantly more damage to pods than Caprice. (Figure 7)

               Plant Injury: Plant injury data cooperates our suspicion that ‘Dragon’s Tongue’ is the most susceptible snap bean variety.  We also saw that ‘King of the Garden’ lima bean sustained a high level of injury, further suggesting that it is more susceptible than the other lima bean varieties. (Figure 8)

 

Objective 1 Discussion:

               Our original goal in this experiment was to determine different type(s) of bush snap bean (puple wax, yellow wax, and common green) were more susceptible or resistant to Mexican bean beetle than others.  Although MBB population counts were not always significant, there was a clear trend, three years in a row of consistently high late larvae populations in purple wax beans, Dragon’s Tongue, followed by yellow wax, Rocdor, and common green, Caprice.  In the third year, were also performed two foliar damage ratings which ranked Dragon’s Tongue as the most susceptible to injury both times, with statistically significant values.  Lastly, on the third year, Dragon’s Tongue also exhibited significantly more pod damage than the other to snap bean varieties.  We believe this is enough evidence to state that this variety is more susceptible to MBB than the other two varieties test. 

Egg numbers were also consistently high in the early samples for all three experiments, suggesting that adult MBB also exhibit preference to this variety.  Although many factors could responsible for making a variety more susceptible and/or preferred, there were a couple noticeable traits exhibited by the Dragon’s Tongue variety that may have made it a better, and more preferred host for MBB.  First, this variety was consistently vigorous, producing large, healthy plants, which were probably very attractive to adult beetles.  Second, its leaves were larger and smoother than the other two varieties.  Not only would these leaves provide greater shade from direct light, but they are probably easier to feed on, given the unique way that MBB gently scrapes the leaf tissue to extract juices.

After the first season, we witness an interesting phenomenon in the Fordhook lima bean variety.  Though adults deposited as many eggs on these plants as the snap bean varieties, fewer late instar larvae were found later in the season.  We suspected that this meant that though the variety was attractive to adults, larvae were less likely to survive.  We wanted to know if this was the case for all lima bean varieties, so we added two more lima beans to our experiments in 2014 and 2015, King of the Garden and Henderson.   Fordhook exhibited similar type of resistance in following years.  King of the garden also harbored high number of eggs followed by lower numbers of instars in 2014; but in 2015 this variety did experience significantly higher numbers of instars than the other lima bean varieties, and greater injury ratings.  Henderson seemed to be the least preferred over, though maybe not any more resistant than Fordhook, as it harbored consistently low numbers of eggs, but did not exhibit a similarly high mortality from egg to larvae.  It may be important to consider that though lima beans may be more resistant to MBB than snap bean varieties, they also require more time to maturity; giving them more time to reach economic injury levels before harvest.

              

              

Objective 2:

(2013 and 2014) Determine if MBB will exhibit host preference among various bean crops, using mark-release-recapture.

 

2013 Cage plot Results:

  • Combined recapture numbers were around 50% on all four sample dates.
  • Immigrated to (Figure 9): The variety Dragon’s Tongue yielded the highest average number of beetles immigrated from other varieties for all four dates. Dragon’s Tongue exhibited significantly higher immigration values than all other varieties on two of four dates: 9/13, 9/17.
  • Remained in original: (Figure 10): ‘Dragon’s Tongue’ had the highest number of beetles that did not leave their original variety, overall. On 9/17, ‘Dragon’s Tongue’ harbored significantly more beetles originally released in that variety, than did any other variety.
  • Immigrated vs. remained: Of the beetles released into Dragon’s Tongue and recaptured, 72% were recaptured in Dragon’s Tongue.  No other group of beetles were recaught in their variety of original release more than 50% of the time.  This was followed by Caprice (46%), Fordhook (37%), Rocdor (29%) and soy (10%).  The total number of recaptures of beetles from each original release variety was not largely different (soy-43, Caprice-51; Rocdor-41, Dragon’s Tongue-52, Fordhook-55).

2013 No-cage plot Results:

  • Total recapture numbers were about 50% lower in the no-cage experiment than cage experiment, and were 29, 32, 20 and 10% from the first to fourth sample date.
  • Overall movement trends were less pronounced than in the cage plot.
  • Immigrated to: Fordhook saw greater immigration numbers overall, but was only significantly different from Caprice and soy on at 24 and 72 hours. Dragon’s Tongue had significantly higher immigration numbers than Caprice and soy at 168h.
  • Remained in original: Rocdor retained significantly more beetles than Fordhook and soy at 48h, and more than soy at 120h.
  • Immigrated vs. remained: 50% of beetles released into Rocdor and recaptured, were recaptured in Rocdor. 49% of beetles released into Dragon’s Tongue and recaptured, were recaptured in Dragon’s Tongue. This was followed by Caprice (35%), Fordhook (21%), and soy (3%).

 

2014 Cage plot Results:

  • Daily percent recapture (of total released) for all varieties combined was 53, 47, 47 and 41% for the four sample dates.
  • Immigrated to. (Figure 11): The variety ‘Dragon’s Tongue’ exhibited the highest average number of beetles emigrated from other varieties for all four dates. ‘Dragon’s Tongue’ exhibited significantly higher emigration values than all other varieties at 120h (9/1) and 168h (9/3).  At 72h (8/30), Dragon’s Tongue had significantly higher immigration values than Fordhook, Rocdor and soy
  • Remained in original (Figure 12): ‘Dragon’s Tongue’ retained more beetles than all other varieties overall. At 24h (8/28) and 120h (9/1), ‘Dragon’s Tongue’ harbored significantly more beetles originally released in that variety, than did any other variety.  
  • Immigrated vs. remained: Of the total number of beetles released into a variety and recaught, 58% of those released into Dragon’s tongue were recaught in Dragon’s Tongue.  No other group of beetles were recaught in their variety of original release more than 50% of the time.  Dragon’s Tongue was followed by Caprice (33%), Rocdor (31%), Fordhook (28%) and soy (0%).  The total number of beetles recaptured among release varieties was nearly uniform except for those released into soy (soy-35, caprice-49; rocdor-49, dragon’s tongue-52, fordhook-49).

2014 No-cage plot Results:

  • Only three beetles were recaptured in the no-cage plot after release. This may have been due to cooler temperatures than in 2013.

 

Objective 2 Discussion:

               The purpose of this study was to gain a better understanding of Mexican bean beetle adult host choice.  Specifically, if various adequate bean hosts are available in similar quantities, will MBB select one variety(ies) over others?  The two experiments conducted in field cages clearly show that adults made a clear choice to not only stay in Dragon’s tongue if they were already in it, but also to leave other varieties to go into Dragon’s Tongue.   Unfortunately, we could not show this in our open plot experiments, probably due to the beetles being affected by too many other stimuli.  However, these data further validate our conclusions from Objective 1, that MBB adults exhibit at least a minor degree of preference to this variety, which also appears to be the most suitable host.   

 

 

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.

 

2013 Results:

  1. Insects Community

  • Mexican bean beetle: Differences we observed at all life stages, and on multiple dates; however, no clear or consistent pattern is apparent.  Larval instars appear to occur in higher numbers in treated replicates, toward the end of both experiments (Fig 13 a&b). 
  • Potato leafhopper: Two dates, 6/14 and 8/16, showed significantly lower PLH numbers in treated replicates by small margins (p = .0237 and p = .0384, respectively).
  • Remaining herbaceous insects: Due to low numbers, all other herbaceous insects were combined for analysis. On 6/17, treated replicates yielded more (p = .0107) of the remaining herbivores; while on 6/28 untreated replicates yielded more of the remaining herbivores (p = .0099).
  • Predatory insects: Predatory insects were largely unaffected by treatment. Combined predaceous ladybird beetles exhibited a difference on 7/8/13; where untreated replicates showed significantly higher numbers (p = .029) than treated replicates. Combined predatory insects showed the same effect, but with a slightly stronger p-value (.0169).

 

  1. Crop Quality

  • First-trifoliate stand count: Significantly more bean plants survived to first-trifoliate stage in treated replicates than untreated replicates for both experiments; however, the difference was much greater in the early experiment (p < .0001) than in the late (p = .004).
  • Harvest stand count (Figure 14 a&b): Significantly more bean plants survived to maturity in treated replicates than untreated replicates in the early experiment (p = .0005), but not in the late.
  • Yield per plot (Figure 15 a&b): Seed treatment plots produced significantly greater yields per replicate than untreated replicates in the early experiment (p < .0001), but not in the late.
  • Yield per plant: Seed treatment replicates produced significantly greater yields per plant than untreated replicates in the first planting (p = .0194), but not in the second.
  • Damaged pods per plot: Proportion of pod damage per plot was unaffected by treatment in both experiments.

 

2014 results:

  1. Insects Community

  • Mexican bean beetle: Only MBB eggs showed any treatment effect.  On 6/17, more eggs were observed in Fungicide only (FG) and Untreated (UT) treatments than Cruiser + Fungicide (CFT) treatments.  Egg masses followed a similar trend; however, UT was not significantly different from either treatment.
  • Potato leafhopper and other herbivores: No treatment effect was observed for PLH or any other herbivorous arthropod in visual counts, pitfall traps or vacuum samples.
  • Predaceous insects: Predaceous insects were mostly unaffected by treatment, with a few exceptions, and no obvious trends exist. Significantly more spiders were observed in CFT treatment than UT and FG treatments on 7/8.  Predaceous ladybird beetles were significantly higher in UT and FG treatments than CFT on 7/2.  

 

  1. Crop Quality

  • First-trifoliate stand count: Significantly more bean plants survived to first-trifoliate stage in CFT than UT treatments; FG was not different from either.
  • Harvest stand count: Number of plants surviving to maturity did not differ among treatments.
  • Total pod yield (Figure 16): CFT treatment had significantly higher yields than FG; UT yield was not different from either.
  • Yield per plant: CFT treatment yielded significantly more fruit per plant than FG; UT was not different from either.
  • Damaged pods per plot: Proportion of pod damage per plot was unaffected by treatment.

 

2015 Results:

  1. Insects Community

  • Mexican bean beetle: No differences were detected among treatments for any life-stage of MBB.
  • Thrips (Figure 17): On 6/4/15, significantly more thrips were found in FG plots than UT and CFT, and significantly more thrips were found in UT than CFT. On 6/11/15, significantly more thrips were found in UT and FG plots than CFT plots. 
  • Herbivores: No other herbivorous insects, including potato leaf hopper, were significantly different among treatments.
  • Predaceous arthropods: No predatory arthropods (spiders, minute pirate bugs, damsel bugs, assassin bugs, predatory stink bugs, lady beetles, ground beetles, and staphylinids) were different on any dates, from any sampling method.

 

  1. Crop Quality

  • Flowering stand count: Significantly more bean plants survived to first-trifoliate stage in CFT and FG than UT treatments. CFT and FG were not different. (Figure 18)
  • Total pod yield: No differences were observed among treatments.
  • Yield per plant: No differences were observed among treatments.
  • Damaged pods per plot: No differences were observed among treatments.
  • Plant health (NDVI): CFT and FG plots had significantly higher NDVI values that UT plots, suggesting UT plots had less biomass than both seed treatment plots. 

 

Objective 3 Discussion:

               Overall the effects of seed treatments are variable, and probably depend of the growing location/region, pest pressure, and climate.  In the first two seasons of the first year, 2013, we saw no fluid or determinant effects to insect populations.  Although differences were observed, highs and lows of pest and predators occurred in both treatments, with no clear trend.  In the first planting, large differences in stand and eventual yield occurred; however, because a fungicide only treatment was not includes, we cannot determine if differences were the effect of the insecticide, the fungicides, or a combination.  This first season also had the greatest difference in insect communities, which could have been result of the insecticide treatment, or the difference in stand density and health. 

               In order to better measure the effects of including an insecticide in the seed treatment, we added a fungicide only treatment to the 2014 and 2015 experiments.  Again, results were variable especially in terms of insect communities.  The only major pest of snap beans we encountered in the past three years was Mexican bean beetle, which was mostly unaffected by the treatments.  In the 2015, we saw a reduction in thrips number in early counts, however, population never reached economic levels in any treatment at any point.  Predators also seem largely unaffected by seed treatments, which we can claim confidently due to numerous sampling methods. 

               In the final two years, yield differences and mature plant stand counts were the same, suggesting that the overall effect of the added insecticide was minimal to crop health.  We do not aim to completely discount the use of these treatments, however.  Again, in our first season, we saw in impressive increase in stand and yield, which could have been the result of pests, pathogens, plant vigor or all three.  Seed treatments may be beneficial only on certain years, at certain planting times, or in certain regions; but those benefits may be significant.  We also reported increase plant health rating (NDVI) in treated plots, but no difference was observed between fungicide only treatment and the Cruiser® + fungicide treatment. 

               Overall, we cannot claim from our results that the addition of Cruiser® insecticide to the seed treatment mixture is particularly necessary, beneficial, or harmful. 

 

 

Objective 4:

(2013) Determine if delayed planting may reduce Mexican bean beetle damage in snap beans.

               (There were no usable results for this experiment)

 

 

Objective 5:

(2014 and 2015) Evaluate the utility of metalized plastic mulch to manage Mexican bean beetle populations and increase snap bean yields.

 

2014 Results:

*Plants on ground plots were much smaller, and less healthy looking than those grown on plastic mulch.  This is likely due to the lack of irrigation used this season.  Though insect numbers were low in these plots, it should be noted that plants were probably less attractive to the beetles, and less total plant area was being searched.

 

Insect counts:   

MBB Eggs (Figure 17): Significantly fewer MBB eggs were found in metalized and white mulch treatments on the second sample date, 7/16/15, than any other black and bare soil plots.  Metalized was had significantly fewer eggs than white plastic plots on this date.  No other dates where significant. 

               MBB Larvae and pupae: Although no significant differences were observed, metalized plots had noticeably lower numbers of early instars, late instars (Figure 18), and pupae (Figure 19) than other treatments in the last three sample dates. 

               MBB adults: Although we believe MBB eggs to be the more accurate measurement of adult activity (since adults are highly mobile and may come and go depending on rapidly changing environmental factors), it should be noted that on the first sample date, 7/9/15 significantly less adults were found in metalized and white plots on the first sample date than ground, followed by black plots.  Metalized also had significantly fewer adults than black and white plots on the second sample date, 7/16/15.

               Predator arthropods (Figure 20): The main purpose of counting predators was to document if reflective plastic mulches may limit predator presence.   We did not find any evidence to suggest that any mulch treatment limited predators, and in fact, three dates showed significantly increased numbers of predators in white and/or metalized plots. 

               Yield (Figure 21): Metalized plots produced significantly greater yield than all other treatments, and over double the amount of bare soil.  Black plastic and white plastic yields were not different from each other, but were significantly greater than bare soil.

 

2015 Results:

*Using drip irrigation alleviated the issue of uneven plant sizes which took place in 2014.

 

Light meter readings (Figure 22)Metalized plots reflected the most light, followed by white. Light intensity on black and ground plots were nearly the same on most dates.  Relative differences among treatments remained consistent throughout the course of the season, even on cloudy and rainy weather.  One data-logger stopped working on 6/26/15, and required service; hence why data ended on this date.

MBB Eggs (Figure 23): Egg numbers were significant on 4 of five sampling dates.  Metalized and white plots were consistently low on these four dates, compared to bare soil.  Metalized plots had significantly less eggs than bare soil plots on four sample dates.  White plots had significantly less eggs than bare soil plots on three sample dates.  Black plots had significantly less eggs than bare soil plots on just the first sample date.

MBB Larvae and pupae (Figures 24, 25, 26):  Metalized and white sustained consistently low numbers of early instars, late instars and pupae throughout the experiment, with many sample dates being significant.  Black plastic actually had relatively high numbers of early and late instars compared to all other treatments, although few pupae were found.

Predatory arthropods:  No differences in any predatory arthropod group were found.

Foliar Injury from MBB (Figure 27):  Both dates showed identical results in terms of treatment effect.  All treatments were significantly different from each other.  The order was as follows from least injury to most injury: Metalized, White, Black, Bare Soil. 

Pod Damage (Figure 28):  Bare soil plots sustained significantly more damaged pods than all other treatments (as well as often being much dirtier from resting on bare ground).  Black plots had significantly more damaged pods than metallized plots, but was not different from white.  White was not different from metalized. 

Bean Yield (Figure 29): Metalized plots produced significantly greater yields than all other treatments, and again, over double that of bare soil plots.  No other treatments were significantly different.

Double Crop Lettuce Yield (Figure 30):   Lettuce double cropped onto used plastic mulch plots did much better than lettuce grown on bare soil.  All plastic mulch treatments produced significantly higher total lettuce yield than bare soil plots, as well as producing cleaner lettuce.  Reflective mulches, white and metalized, were not different from each other, and both produced higher yields than black plastic.  Metalized had the greatest average weight numerically. 

 

Objective 5 Discussion:

               Our goal in this experiment was to determine if reflective plastic mulches (metalized and white) may reduce injury from MBB to snap beans compared to bare soil and non-reflective plastic mulch (black).  Both years of this experiment exhibited promising results.  The metalized treatment performed particularly well in, followed by white plastic.  Overall, metalized plots harbored very few MBB adults, eggs and late larvae compared to all other treatments.  White plastic show similar trends, but less profound.  Black plastic and bare ground both harbored relatively high numbers of all life stage. 

               Foliar damage, pod damage and yield were especially profound metalized treatments. Damage was consistently lower in metalized plots, followed by white, black and bare ground, respectively.   Metalized plots produced impressive increases in yield, especially compared to bare soil.  It is also important to note that more of these pods were marketable, as they had less damage from MBB and were cleaner from being on plastic instead of bare soil.  Light sensor readings suggest that there is a correlation between increased light intensity and reduced MBB presence and injury.   These finding suggest that planting beans on metalized plastic can provide benefits in terms of MBB management, and plant productivity. 

               Because metalized plastic mulch is more expensive than black plastic (and obviously bare soil), we wanted to see if growers would be able to get more economy out of their investment by planting a second crop on the used plastic.  We chose lettuce, as it is a common late summer crop that requires very little fertilizer and pesticide inputs.  We were delighted to see that this crop also performed impressively well on reflective mulches.  Both metalized and white plastic mulch treatments produced significantly greater yields than black plastic and bare soil, and black plastic also had significantly higher yields than bare soil.  

                        

Participation Summary

Educational & Outreach Activities

Participation Summary

Education/outreach description:

Peer reviewed publications:  

 

  1. B. Nottingham, G. P. Dively, P. B. Schultz, D. A. Herbert and T. P. Kuhar. In review. Natural History, Ecology and Management of the Mexican bean beetle (Coleoptera: Coccinellidae) in the U.S. Journal of Integrated Pest Management.

 

Abstracts:

 

  1. B. Nottingham and T. P. Kuhar. 2014. Investigating the Movement and Host Selection of Mexican bean beetle, Epilachna varivestis, among Five Host Plants using Mark-Release-Recapture. Virginia Journal of Science. Vol. 65 1&2.

 

 

Fact Sheets:

 

  1. B. Nottingham and T. P. Kuhar. 2013. Mexican bean beetle. Virginia Cooperative Extension Pub: ENTO-51NP.

 

  1. B. Nottingham and T. P. Kuhar. 2014. History, Distribution, and Pest Status of the Mexican bean beetle. Virginia Cooperative Extension Pub: ENTO-62NP.

 

  1. B. Nottingham and T. P. Kuhar. 2015. Pediobius foveolatus– A Parasitoid of the Mexican bean beetle. Virginia Cooperative Extension Pub: ENTO-170NP.

 

Outreach:

 

Virginia Tech’s Kentland Research farm holds several field days every year, in which we have had the opportunity to display our plots and discuss these experiments with farmer and gardeners.  We also travel to various venues, such as community gardens and expos, throughout the course of the year where were interact and share our experimental findings. Dr. Kuhar has also presented results of these studies at several commercial vegetable grower meetings in Virginia and one in North Carolina. 

Project Outcomes

Project outcomes:

The results of these studies could have a major impact on insect pest management in snap beans in the mid-Atlantic U.S. Our newfound knowledge that Mexican bean beetles prefer certain bean varieties over others could help in the development of a trap crop management approach, where beetles are drawn to an attractive trap crop where they can be concentrated and killed.  Use of ‘Dragon’s Tongue’ wax beans for instance would be an excellent choice for this strategy.  Our results showing the pest management benefits of growing snap beans on ‘metalized’ plastic mulch should open the door to that area of pest management and production for snap beans, as that technique has not been well studied on that crop.  Because we witness reduced insect damage and yield increases of over 100%, two year in a row, in bean plants on ‘metalized’ plastic mulch compared to bare ground, we hope to see this method adopted by growers in the near future.  In addition, studies on the impacts of thiamethoxam insecticidal seed treatments in snap bean systems will be useful for decision making by growers on whether they might want to consider that preventative control tactic.  As we continue to present the results of these studies at grower meetings, we believe that we will increase the grower’s education of this pest and offer alternative strategies to managing it, which should help improve the sustainability of snap bean production.             

Economic Analysis

‘Metalized’ plastic mulch is roughly $45 for 200′, compared to black plastic, which can be purchased for about $30 at that length.  However, if a grower purchases in bulck, such as 4000′, the prices are the same: about $245 for 4000′.  We have shown that growers can over double their yield by planting beans on metalized plastic instead of bare soil, which that alone will quickly offset the cost of the mulch.  Also, mulch should reduce costs associated with insecticides, herbicides (since the plastic creates a weed-free zone around the plant), and reduced unmarketable pods cause by pathogens obtained from soil contact.  Also, growers can choose to plant a second crop, such as lettuce, on the same plastic and receive similar benefits in yield, weed control, and cleanliness.

Farmer Adoption

Most of the preliminary findings in these experiments are available in the published fact sheets mentioned in the Publication/Outreach section.  These factsheets are readily available on the Virginia Cooperative Extension website.  We also distribute hard copies at field days, expositions, and grow conferences.  The total number of growers reached through this means is obviously difficult to estimate; but we do know that the information is readily available to anyone who is interested in these topics.  I have given ten total grower talks.  Each talk has between 15-40 people in the audience.  So the information from my research has reached at least 150-400 people directly.

Currenty, I do not make direct recommendations, as our results have yet to be peer-reviewed, or replicated by other researchers.  However, I do encourage people to implement certain strategies at their own risk; especially hobby growers who do not have large financial stake in outcomes.  Because our plastic mulch study is very applied and produced clear results, I encourage growers to try planting beans on metalized mulch, especially if they encounter large populations of Mexican bean beetle.  I also let them know that they can follow up their bean crop with anything that grows well in the late summer to fall.   I also inform growers that Dragon’s Tongue variety is very susceptible to MBB; so if they have regular MBB populations, they should plan a management strategy ahead of time.  I will mention strategies that I have worked on, and those that I have only reviewed literature; which include: using reflective mulch, planting early or late, using Pediobius foveolatus, or using a well-timed insecticide spray, at first presence of early instars. 

Early planted seeds are more susceptible to pathogens and soil pests, because they generally take longer to germinate.  If growers plant seeds early, using treated seed (with or without a systemic neonicotinoid) is a smart choice, as it seems to improve plant health and stand quality.  Also, because treated seeds (with or without a systemic neonicotinoid) are nearly the same price as untreated seed (around 10 cents more per pound), the economic risk is extremely low.  For growers that are concerned about adding additional chemicals into the system, I recommend planting beans two or three weeks past the last frost date.  The ground is warm enough, and usually spring rains are less extreme at this point, so beans come up fast and healthy whether or not treated seeds are used.    

Recommendations:

Areas needing additional study

               Understanding the specific mechanism(s) causing dramatic yield increases on metalized plots is an area that should be further addressed.  Although some benefits may be due to reduced damage from MBB, we suspect that there are other horticultural factors that are enhancing this effect, such as soil temperature, soil moisture retention, plant photosynthetic efficiency, etc.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.