Biology, Yield loss and Control of Sclerotinia Stem Rot of Soybean

Bean Leaf Beetle (Coleoptera: Chrysomelidae) and Bean PodMottle Virus in Soybean:Biology, ecology, andmanagement

Buyung A. R. Hadi,1,2 Jeffrey D. Bradshaw,3 Marlin E. Rice,4 and John H. Hill5

1Plant Science Department, South Dakota State University, Brookings, SD 57007.2Corresponding author, e-mail: [email protected] of Entomology, Panhandle Research and Extension Center, University of Nebraska, Scottsbluff, NE 69361.4Pioneer Hi-Bred International, Inc., Johnston, IA 50131.5Department of Plant Pathology, Iowa State University, Ames, IA 50011.

J. Integ. Pest Mngmt. 3(1): 2012; DOI: http://dx.doi.org/10.1603/IPM11007

ABSTRACT. Bean leaf beetle, Cerotoma trifurcata (Forster), is a pest of soybean found inmany production areas in theUnited States. Thebean leaf beetle larvae feed on soybean root nodules, whereas the adults feed on the above ground parts of soybean such as cotyledon,leaves, and pods. Bean leaf beetle is also a very efficient vector of Bean podmottle virus, a widespread virus of soybean in the south andsoutheastern United States with recent expansion into the north central region of the country. This article summarizes bean leaf beetlebiology, ecology, and its impact on soybean production in the United States. The management of this insect and Bean pod mottle virusas recommended in the north central states is also presented.

Key Words: bean leaf beetle, Cerotoma trifurcata, bean pod mottle virus, soybean

The bean leaf beetle, Cerotoma trifurcata (Forster), is a pest of soybeans,Glycines max (L.) in most soybean growing regions of the United States.Adults feed on cotyledons, leaves, and pods, whereas larvae feed onsoybean nodules attached to the roots. Furthermore, bean leaf beetles alsotransmit Bean pod mottle virus, a widespread virus of soybean. Bean leafbeetles can be found in major soybean production areas in the UnitedStates (Turnipseed and Kogan 1976, Pedigo 1994). The biology of beanleaf beetle, both as a pest of soybean and a vector of Bean pod mottlevirus will be discussed, followed by a section of management of bean leafbeetle and Bean pod mottle virus with emphasize on recommendationsfor the north central states.Identification. The bean leaf beetle is a member of the family

Chrysomelidae in the order Coleoptera. Adults are variable in color,ranging from red to orange to light yellow (Fig. 1). When adults firstemerge from the soil, their elytra (wing covers) are soft and the bodyis often beige in color (Fig. 2). Four squarish black markings arecommon on the elytra; however, these markings can be as few as twoor none. The elytra are usually rimmed by a black margin. A blacktriangle, termed the scutellum, is always present immediately behindthe pronotum (Pedigo 1994) (Fig. 3) regardless of whether the insecthas four, two, or no black “squares” on the elytra. Female beetles oftenhave black frons (face), whereas the male beetles usually have tanfrons (Kogan et al. 1980). In addition, the base of a male beetle’s firsttarsal segment has a patch of dense setae (hairs) thought to be involvedin the mating process (Hammack and French 2007). Female beetleslack this morphological feature.

Bean leaf beetle eggs are lemon-shaped and orange in color, and theyare found in soil around the base of soybean plants (Pedigo 1994). Thesubterranean larva is elongate, white in color with dark brown plates onboth ends of the body (Fig. 4). The dark brown color comes fromsclerotization of the larva’s head and last abdominal segment. Larvae cangrow to 0.4 inch (10 mm) long, are cylindrical in shape, and similarlooking to corn rootworm (Diabrotica spp.) larvae. The pupae are white,�0.2 inch (5 mm) long, and enclosed within earthen cells.Host Plant. Bean leaf beetles have a large host range, mostly on

leguminous plants including clover (Trifolium spp.) and soybean(Bradshaw et al. 2007); however, they also have been reported to feedon nonleguminous hosts such as cucurbits (Koch et al. 2004), stingingnettle (Urtica dioica L.), and Canadian woodnettle [Laportea ca-nadensis (L.)] (Helm et al. 1983).

Life Cycle and Seasonal History. Bean leaf beetles overwinter asadults and are able to withstand temperatures below the water freezingpoint. In a laboratory study, Lam and Pedigo (2000a) found thatexposing winter-acclimated adult beetles for 12 minutes below 14°F(�10°C) resulted in 50% mortality, yet it took 400 hours at temper-atures between 23° and 14°F (�5 and �10°C) to kill the sameproportion of beetles. Carillo et al. (2005) reported that bean leafbeetles collected in different months in a year had varying degrees ofcold hardiness. Most beetles collected between September to Marchwere able to survive lower temperatures than beetles collected duringthe rest of the year. Bean leaf beetle adults survive winter under leafdebris in woodlots and crop residue in soybean fields. Survival rate ofoverwintering bean leaf beetles is higher in sheltered habitats (e.g.,woodlands) compared with exposed habitats (e.g., soybean fields)(Lam and Pedigo 2000b). A measurement of daily temperature duringwinter in Iowa showed that woodland leaf litter can maintain temper-atures above 23°F (�5°C), which contributes to higher survival rate ofoverwintering bean leaf beetles in this habitat (Lam and Pedigo2000a). In the extreme southern United States, the beetles may noteven hibernate at all (McConnel 1915).

Surviving adults begin to emerge from their overwintering sites at50–55°F (10–12.7°C) (Boiteau et al. 1979a, Jeffords et al. 1983,Loughran and Ragsdale 1986). The beetles mate and disperse to varioushosts such as alfalfa (Medicago sativa L.) and other legumes such as ticktrefoil (Desmodium spp.) and clover (Smelser and Pedigo 1991, Brad-shaw et al. 2007). Bean leaf beetle adults move to soybean, their apparentpreferred host, as the soybean seedlings emerge (Figs. 5 and 6).

Female bean leaf beetles enter soybean fields gravid (i.e., matedand carrying eggs) and lay small clusters of eggs within 1.5 inches (3.8cm) of the soil surface and within a 2-inch (5.1 cm) radius of thesoybean plant (Waldbauer and Kogan 1975). Each female lays 130–200 eggs throughout its lifetime (Pedigo 1994). When given a choice,female beetles preferred to lay their eggs in an organic soil rather thanin sandy clay loam or loamy sand (Marrone and Stinner 1983a). Inaddition, Marrone and Stinner (1983a) also found more eggs in wet ormoist soils than in dry soils. Bean leaf beetle eggs take a week to hatchat 82.4°F (28°C). Both very wet and very dry soils are detrimental tothe eggs. Coincidental with oviposition preference, egg survival wasthe greatest when kept in saturated organic soil as compared withloamy sand and sandy clay loam (Marrone and Stinner 1983b).

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Bean leaf beetle larvae feed in the soil on soybean roots and rootnodules (Pedigo 1994, Lundgren and Riedell 2008). Larvae developthrough three stages before pupating in the soil. The larvae are capableof moving in the soil and under dry soil conditions can move up to11.8 inches (30 cm) per hour in search of moisture (Marrone andStinner 1983c). The type of soil in which the larvae forage for foodaffects the larval survivorship. Cuticle abrasion associated with thesoil’s sand content is detrimental to larvae. Under moist soil condi-tions, larvae survived best in organic soil (0–4% mortality) comparedwith loamy sand (87–100% mortality) and sandy clay loam (0–20%mortality) (Marrone and Stinner 1983c).

Development from egg to adult requires 674–740 DD in °F (374–411 DD in °C), with the lower development threshold at 46°F (7.8°C)(Zeiss et al. 1996). Beetles emerging from the soil form the firstgeneration of adults for a given year. Depending on the timing ofemergence in relation to the stage of soybean development, adultbeetles may mate again and deposit eggs or they may overwinter untilthe subsequent year. Bean leaf beetles produce three generations per

year in the southern United States (Pedigo 1994), two generations inthe central states of Illinois (Waldbauer and Kogan 1976), Iowa(Smelser and Pedigo 1991), and Nebraska (Danielson et al. 2000), andonly one generation in Minnesota (Loughran and Ragsdale 1986).

Adults readily disperse by flight. In a laboratory study character-izing the beetle’s flight capacity, the majority of sampled beetlesshowed short distant flight of �167 feet (�51 m) in a 24-hour period.A little over 11% of the beetles showed medium range flight capacity�987 feet (�301 m) and one beetle flew 3 miles (4.9 km) in a 24-hperiod (Krell et al. 2003b).

In the field, bean leaf beetle populations are often highly aggre-gated along field edges (Kogan et al. 1974, Boiteau et al. 1979b,Smelser and Pedigo 1992a). It is not known whether the aggregatedspatial pattern of bean leaf beetle in the field is maintained under veryhigh population levels as observed in outbreak years.Plant Injury and Damage. Bean leaf beetle larvae feed on soybean

root nodules. Soybean compensates for larval feeding by producingadditional nodules. However, high larval infestation (19 larvae perplant) may cause smaller root nodules and reduce leaf and pod

Fig. 1. Variation in adult bean leaf beetle, Cerotoma trifurcata, body coloration.

Fig. 2. Newly-emerged bean leaf beetle, Cerotoma trifurcata.

Fig. 3. Adult bean leaf beetle, Cerotoma trifurcata, can always berecognized by the black triangular spot behind the pronotum (A).Most adults also have four large squarish markings on the elytra (B),and a black rim on the elytra (C).

Fig. 4. Bean leaf beetle, Cerotoma trifurcata, larvae.

Fig. 5. Overwintered generation of bean leaf beetle, Cerotomatrifurcata, moving to soybean seedlings.

2 JOURNAL OF INTEGRATED PEST MANAGEMENT VOL. 3, NO. 1


nitrogen content (Lundgren and Riedell 2008). The potential eco-nomic damage because of root feeding by larvae is not clearlyunderstood.

Adults feed on the above ground parts of soybean such as cotyle-dons, leaves and pods (Figs. 7-9). Beetle feeding may commence atthe leaflet edge or in the middle of the leaflet producing round holesin the tissues between leaf veins. The round holes produced by adultfeeding are generally distinct from more jagged-edged feeding holesproduced by grasshoppers and caterpillars (Smelser and Pedigo1992b).

The impact of adult feeding is dependent on the plant’s growthstage. A single adult feeding on soybean during vegetative stages(V1-V3, �14 days) is estimated to consume up to 5.48 inches2 (13.93cm2) of foliage (Hunt et al. 1995). Hunt et al. (1994) found that areduction of cotyledon and seedling tissue delays canopy developmentand reduces yield. Sequential removal of 68% soybean seedling tis-sues between V1-V3 stages resulted in a 12% yield reduction (Hunt etal. 1994). It has been noted that soybean plants tolerate defoliationeither by delayed leaf senescence or compensatory leaf regrowth. Thiscompensatory response can offset foliage loss because of bean leafbeetle feeding (Haile et al. 1998). Defoliation tolerance seems todepend on an optimum growth environment, thus in drought years thistolerance may be limited. Turnipseed (1972) removed soybean leaves

manually between blooming and pod set (R1-R4) to show that yieldloss occurs at high levels of defoliation (above 50%). Adults feedingon later stage soybean plants may contribute additively to the overallimpact of defoliation when they occur with other leaf feeding insects.It has been estimated that, on average, an adult beetle feeding on R6soybean for two weeks may reduce as much as 0.0074 ounce (0.21 g)of seed weight (Smelser and Pedigo 1992c).

During seed filling, bean leaf beetles may feed on the pod surface.Although root-feeding larvae and leaf-feeding adults may affect seedyield and quality, pod feeding inflicts direct injury on the seeds. Thefeeding injury on the pod surface acts as an entry point for bacterialand fungal secondary infection, and the scarring of soybean podsexposes the seeds to excess moisture. The seeds on scarred pod maybecome shrunken, discolored, and moldy. Bean leaf beetles also feedon the soybean pod peduncle, sometimes clipping the pod in theprocess. Smelser and Pedigo (1992c) found no significant differencein seed weight, and number of seeds per plant between several levelsof bean leaf beetle infestation. However, in a drought year of 1988,Smelser and Pedigo (1992b) documented that an average of 0.125 podper beetle was lost each day because of beetle feeding on podpeduncles.Bean leaf beetle as Bean pod mottle virus vector. Bean pod mottle

virus is a member of the genus Comovirus in the family Secoviridae(Sanfacon et al. 2009). The first incidence of Bean pod mottle virus in

Fig. 6. Leaf injury and cotyledon scarring because of adult bean leafbeeetle, Cerotoma trifurcata, feeding.

Fig. 7. Soybean seedling injury from bean leaf beetle, Cerotomatrifurcata.

Fig. 8. Defoliation inflicted by bean leaf beetle, Cerotoma trifurcata.

Fig. 9. Pod injury from bean leaf beetle, Cerotoma trifurcata,feeding.

MARCH 2012 HADI ET AL.: BEAN LEAF BEETLE AND VIRUS IN SOYBEAN 3


the United States was reported on common bean (Phaseolus vulgarisL.) in South Carolina (Zaumeyer and Thomas 1948) and the firstreported incidence on soybean was from Arkansas (Walters 1958).The incidence of Bean pod mottle virus is widespread in majorsoybean growing regions in the south and southeastern United States;more recently increased incidence has been documented in soybeanthroughout the north central United States (Giesler et al. 2002).

Depending on the soybean variety and the virus strain, infectedsoybean may show symptoms ranging from chlorotic mottling, severemosaic to leaf distortion (Fig. 10) and leaf necrosis. The most obvioussymptoms occur in plants infected early in the season or duringperiods of rapid growth. Symptoms are more clearly shown in lowambient temperatures (Gergerich 1999). Bean pod mottle virus infec-tion has been associated with a disorder known as “green stem”. Thestems of plants showing green stem disorder stay green (Fig. 11) evenas they bear normal mature pods. This condition may have an impacton soybean harvest as the green stems are more difficult for harvestingmachinery to cut. Contradictory results have been reported on therelationship between Bean pod mottle virus infection and green stemdisorder (e.g., Goh et al. 2004, Hobbs et al. 2006), and the precisecause of the green stem disorder remains unclear.

Soybean infected by Bean pod mottle virus produces 3–52% lessyield depending on the soybean variety and the time of infection.Virus infection occurring in early vegetative stages (VC-V3) causes

the highest yield reduction (Ziems et al. 2007). The seeds produced byBean pod mottle virus-infected soybean may show mottled seed coats(Fig. 12), reducing the quality of the seed (Hobbs et al. 2003, Hill etal. 2007). Bean pod mottle virus infection on soybean also increasesthe risk of Phomopsis seed infection (Abney and Ploper 1994). Co-infection of Bean pod mottle virus and Soybean mosaic virus leads tosynergistic infection where Soybean mosaic virus presence increasesthe titer of Bean pod mottle virus (Anjos et al. 1992), which translatesinto dramatic reduction of yield (Ross 1968) and root nodules (Tu etal. 1970) of co-infected soybean plants.

Bean pod mottle virus is transmitted by several leaf feeding beetlesin North America, including bean leaf beetle, grape colaspis [Colaspisbrunnea (F.)], banded cucumber beetle (Diabrotica balteata Le-Conte), spotted cucumber beetle (Diabrotica undecimpunctata how-ardi Barber), striped blister beetle [Epicauta vittata (F.)], and Mexicanbean beetle (Epilachna varivestis Mulsant) (Gergerich 1999). Beanleaf beetle is an extremely efficient Bean pod mottle virus vector; upto 80% of beetles feeding on Bean pod mottle virus-infected soybeanfor three days were able to transmit the virus to healthy plants (Giesleret al. 2002). In addition, bean leaf beetle transmits Cowpea mosaicvirus and Southern bean mosaic virus (Boethel 2004). Of all thesoybean viruses transmitted by bean leaf beetle, Bean pod mottle virusis considered to be the most prevalent and widespread in the U.S.soybean producing regions (Tolin and Lacy 2004).

Theoretically, there are at least three sources of primary Bean podmottle virus inoculum in summer soybean introduction: soybean seedsinfected with the virus, virus from previous year’s epidemic retainedin overwintering bean leaf beetles, and virus-infected leguminousweeds. Seed infection of Bean pod mottle virus occurs at a very lowrate and seed coat mottling is not a good indicator of seed infection asmottling may still occur without virus presence within the seed (Krellet al. 2003a). Overwintering bean leaf beetles have been shown toretain Bean pod mottle virus from the previous year albeit in a verylow frequency (Krell et al. 2003a). Bean pod mottle virus infects arange of mostly leguminous hosts including soybean and dry bean.Tick trefoil, a perennial leguminous weed, was found to host Bean podmottle virus in nature (Krell et al. 2003a, Bradshaw et al. 2007). Beetlesemerging from overwintering habitats and feeding on infected perennialtick trefoil may acquire the virus. When soybean seedlings emerge, thebeetles move to these plants, transmitting the virus. The subsequentgeneration(s) of bean leaf beetle may continue to spread the virus withinand between soybean fields during the growing season.Management Approaches. The first part of this section describes

management approaches of bean leaf beetle in the absence of Beanpod mottle virus. If a particular field’s history included incidences ofBean pod mottle virus and virus-related loss of yield quantity andquality, a different management approach is recommended. Bean leafbeetle management in the presence of Bean pod mottle virus historyis discussed under the heading “Management of Bean Leaf Beetle inthe Presence of Bean Pod Mottle Virus.”

Fig. 10. Soybean leaf distorted by Bean pod mottle virus.

Fig. 12. Normal soybean seed (left) and infected seed with Beanpod mottle virus (right) showing the “bleeding” hilum.

Fig. 11. Soybean field (foreground) showing a streak of “greenstem”.



Scouting and Threshold. Scouting for bean leaf beetle can be doneby direct observation, sweep net, or ground cloth. The description ofscouting techniques described here is drawn largely from Kogan et al.(1980). Some thresholds are based on the field estimation of percentdefoliation or pods injured from beetle feeding activity while otherthresholds are directly based on the sampling of bean leaf beetlepopulation in the field.

Direct observation may accurately estimate early-season (VC–V4stage) bean leaf beetle populations. This observation estimates theabundance of overwintering beetles from the previous year. Randomlyselect five 16–32 feet (5–10 m) row-lengths from across the entirefield. At each sampling site, walk slowly and carefully count allbeetles. Make sure that beetles on the underside of the leaves arecounted by gently turning the leaves over. Cool early-morning hoursare probably the best time to conduct the observation as the beetles arerelatively inactive. At the end of sampling, the average number ofbeetles per row-foot or, given a fixed inter-row spacing, the number ofbeetles per plant can be calculated.

In conventional soybean cropping system (the rows are �30 inches[76 cm] apart), the ground cloth technique is reliable in moderate tohigh beetle population levels (defined as the number of beetles perrow-3 feet [1 m] �10) while the sweep net is reliable at all populationlevels. Both techniques are used when the soybean plants are too largefor direct observation. These techniques are essential in estimating thefirst and subsequent generations of bean leaf beetles in soybean fields.Deighan et al. (1985) noted that ground cloth sampling producedbetter estimates of bean leaf beetle population in conventional crop-ping system than in drill-planted soybean.

Five to eight sampling sites should be chosen randomly across thefield for sweep net scouting. On each site, walk between two rows and

swing a sweep net upward and downward on a row (not across rows) withsuccessive steps (Video Clip 1: Sweep net sampling technique on soy-bean [video-Marlin E. Rice]). Count each stroke of the net as a sweep and10–20 sweeps per sampling site should be conducted. Bean leaf beetlesare counted after each sampling unit. At the end of sampling, the averagecount of bean leaf beetles per sample site can be calculated.

An example of equipment used for ground cloth sampling consistsof a white cloth measuring 36 by 42 inches (0.91 by 1 m) with stripsof wood, �one-half by 1 inch (1.27 by 2.54 cm) wide, stapled to eachlong side of the cloth. Sample at least five randomly chosen samplingsites across the field. In each site, roll the cloth beneath the canopyfrom one row over to the next row without disturbing the foliage (Fig.13). Vigorously shake the plants from both rows over the ground clothby using both hands and forearms. Count the beetles collected on thecloth. This way, two 3-row feet (0.91 row m) sections (a total of 6 feet,or 1.82 m) are sampled. If some insects can’t be identified on the field,collect several specimens for later identification. By the end of sam-pling, the average count of beetle per row-foot or row-meter can becalculated.

Hunt et al. (1995) reported a matrix of EILs of overwintered beanleaf beetle on early soybean seedlings (VC-V2) for various scenariosof market value per production unit and control cost per area. Assum-ing the economic threshold to be equal to 75% of the economic injurylevel (EIL) presented by Hunt et al. (1995), Rice et al. (2005) sum-marized the economic threshold values as represented in Table 1. Theeconomic threshold values in Table 1 represent uncommonly highpopulation densities of overwintered bean leaf beetles (Hunt et al.1995).

In areas where there are only two generations of bean leaf beetlesper year, the need to control the second generation beetle can bedetermined by sampling the first generation (Lam et al. 2000). Thissampling scheme was developed in Iowa and its validity has not beentested elsewhere. This scheme is based on a positive correlationbetween the population size of first generation beetle and the popu-lation size of second generation beetle in a given year in Iowa (Lamet al. 2001, 2008). Using the Lam et al. (2000) sampling plan, scoutingshould begin 1 wk after the peak emergence of first generation beetles.The peak emergence time can be estimated by accumulating 1,212 DDin °F (673 DD in °C), with base temperature of 46°F (7.78°C), startingat soybean emergence. First generation bean leaf beetles can besampled using sweep net or ground cloth. A set of threshold values forthe first generation beetle, represented as the number of beetles caughtusing drop cloth and sweep net, are given consecutively in Table 2 and3 (Lam et al. 2000). If in the first scouting the beetle population doesnot exceed the threshold, scouting should be repeated 1 week later. Ifin the second scouting the beetle population still does not exceed thethreshold, scouting is repeated in the third and final week. If after threescouting efforts the bean leaf beetle population never exceeds thethreshold, no economic damage should occur from the second gener-ation bean leaf beetle infestation and no control action is necessary the

Fig. 13. Drop cloth positioning for bean leaf beetle sampling insoybean.

Table 1. Economic threshold of overwintered bean leaf beetle in 30-inch row early-stage soybean (beetles per plant) (Hunt et al. 1995,Rice et al. 2005)

Market valueGrowth stage/cost of treatment, $/acre ($/bu)

VC V1 V2

$/Bu ($/kg) 6 (14.8) 10 (24.7) 14 (34.6) 18 (44.5) 6 (14.8) 10 (24.7) 14 (34.6) 18 (44.5) 6 (14.8) 10 (24.7) 14 (34.6) 18 (44.5)

5.00 (0.18) 2.5 4.1 5.8 7.4 3.8 6.3 8.9 11.4 6.0 9.9 13.9 17.910.00 (0.36) 1.2 2.1 2.9 3.7 1.9 3.2 4.4 5.7 3.0 5.0 7.0 9.015.00 (0.54) 0.8 1.4 1.9 2.5 1.3 2.1 3.0 3.8 2.0 3.3 4.6 6.0

These values are calculated by using the formula: ET � 0.75*(C/VIDK). Where ET is Economic threshold, C � cost of management per production unit, V �market value per production unit, I � injury units per insect per production unit, D � damage per production unit and K � proportionate reduction of theinsect population. It is assumed that for VC growth stage, D � 1.33 (from regression based on an expected yield of 34.4 bu/acre), I � 18.79, and K � 1 (totalcontrol); for V1, D � 1.33, I � 12.20 and K � 1; for V2, D � 1.33, I � 7.78 and K � 1 (Hunt et al. 1995).



next (e.g., second) generation. If the threshold is exceeded in one ofthe three scouting efforts, Lam et al. (2000) recommends a controlaction; however, the timing of control action should correspond withthe emergence of the later second generation population in the soy-bean field (Rice et al. 2005).

A more general approach to set an economic threshold for beanleaf beetle is by using the defoliation rate because of bean leaf beetlefeeding activity. Overwintered beetles feed on seedling soybean andtreatment is warranted if over 20–30% of the seedlings in the field aredestroyed. Treatment is also warranted if defoliation exceeds 30–50%during other vegetative stages of soybean development. Adults fromthe first generation bean leaf beetles feed on soybean leaf around Julyin the north central United States and should be treated if defoliationrate exceeds 15–35% during bloom (R1-R2). During pod-set andpod-fill (R3-R6), a field should be treated if defoliation exceeds 25%.Because bean leaf beetles also feed on pods, damage to pods shouldalso be monitored. Control is warranted if pod injury exceeds 10%during pod-fill (Zeiss and Klubertanz 1994, University of MinnesotaExtension 2006, Knodel et al. 2009).Cultural Methods. Delayed soybean planting date may reduce bean

leaf beetle abundance (Pedigo and Zeiss 1996). Planting soybean aslate as possible within the recommended planting period for a varietymay reduce initial and subsequent beetle densities, although main-taining yield potential. A potential risk is of note when late-plantedsoybean fields were located next to early-planted fields. In this situ-ation, beetles from early-planted fields may easily migrate to late-planted fields, rendering planting date strategy ineffective.

Management of Bean Leaf Beetle in the Presence of Bean PodMottle Virus. Delayed soybean planting date has been suggested as aBean pod mottle virus management tactic (Giesler et al. 2002), but 3-yrfield data from Iowa showed that delayed planting did not consistentlyresult in lower Bean pod mottle virus infection (Krell et al. 2005).

The use of soybean varieties with antixenosis (i.e., physical resis-tance) against bean leaf beetles does not sufficiently reduce Bean podmottle virus incidence and spread in the field (Redinbaugh et al.2010). No soybean varieties with resistance against Bean pod mottlevirus have been reported although some varieties have some tolerance(Hill et al. 2007, Ziems et al. 2007).

Insecticide seed treatment by using neonicotinoid insecticides (VideoClip 2: The effect of seed treatment on soybean on overwintered bean leafbeetle [video-Marlin E. Rice]) or foliar pyrethroid insecticides betweenemergence and first trifoliolate reduces total Bean pod mottle virusincidence, likely by protecting soybean seedlings from early beetle pop-ulations (Krell et al. 2004, Bradshaw et al. 2008). Additional applicationsof foliar insecticides by using foliar pyrethroid insecticides midseason(around blooming), aimed at controlling the first generation of bean leafbeetle, may further suppress virus incidence (Krell et al. 2004, Bradshawet al. 2008).Summary. The bean leaf beetle is an occasional pest of soybean but

occurs in most soybean producing areas of the United States. Thus, thepotential for economic injury exists in many soybean productionsystems, especially in the north central states. The biology, sampling,and management considerations described are intended to reduce theeconomic impact of this pest, including its role in transmitting Beanpod mottle virus. Effective management of the insect requires anunderstanding of pest ecology, timely scouting, and the application ofappropriate control measures when economically warranted.

References CitedAbney, T. S., and L. D. Ploper. 1994. Bean pod mottle virus effects on soybean

seed maturation and seedborne Phomopsis spp. Plant Disease 78: 33–37.Anjos, J. R., U. Jarlfors, and S. A. Ghabrial. 1992. Soybean mosaic potyvirus

enhances the titer of two comoviruses in dually infected soybean plants.Phytopathology 82: 1022–1027.

Boethel, D. J. 2004. Integrated pest management of soybean insects, pp.853–881. In: H. R. Boerma and J. E. Specht (eds.). Soybeans: improvement,production and uses, 3rd ed. ASA/CSSA/SSSA, Madison, WI.

Boiteau, G., J. R. Bradley, and J. W. Van Duyn. 1979a. Bean leaf beetle:Emergence patterns of adults from overwintering sites. Environmental En-tomology 8: 427–431.

Boiteau, G., J. R. Bradley, J. W. Van Duyn, and R. E. Stinner. 1979b. Bean leafbeetle: micro-spatial patterns and sequential sampling of field populations.Environmental Entomology 8: 1139–1144.

Bradshaw, J. D., M. E. Rice, and J. H. Hill. 2007. No-choice preference ofCerotoma trifurcata (Coleoptera: Chrysomelidae) to potential host plants ofBean pod mottle virus (Comoviridae) in Iowa. Journal of Economic Entomol-ogy 100: 808–814.

Bradshaw, J. D., M. E. Rice, and J. H. Hill. 2008. Evaluation of managementstrategies for bean leaf beetles (Coleoptera: Chrysomelidae) and Bean podmottle virus (Comoviridae) in soybean. Journal of Economic Entomology101: 1211–1227.

Carrillo, M. A., R. L. Koch, E. C. Burkness, K. Bennett, D. W. Ragsdale, andW. D. Hutchison. 2005. Supercooling point of bean leaf beetle (Coleoptera:Chrysomelidae) in Minnesota and a revised predictive model for survival atlow temperatures. Environmental Entomology 34: 1395–1401.

Danielson, S. D., J. R. Brandle, L. Hodges, and P. Srinivas. 2000. Bean leaf beetle(Coleoptera: Chrysomelidae) abundance in soybean fields protected and unpro-tected by shelterbelts. Journal of Entomological Science 35: 385–390.

Deighan, J., R. M. McPherson, W. F. Ravlin. 1985. Comparison of sweep-net andground-cloth sampling methods for estimating arthropod densities in differentsoybean cropping systems. Journal of Economic Entomology 78: 208–212.

Gergerich, R. C. 1999. Bean pod mottle, pp. 61–62. In G. L. Hartman, J. B.Sinclair, and J. C. Rupe (eds.), Compendium of soybean diseases, 4th ed.APS Press, St. Paul, MN.

Giesler, L. J., S. A. Ghabrial, T. E. Hunt, and J. H. Hill. 2002. Bean pod mottlevirus: a threat to U.S. soybean production. Plant Disease 86: 1280–1289.

Goh, Y. K., J. S. Russin, S. A. Ghabrial, J. P. Bond, and M. E. Schmidt. 2004.Soybean green stem caused by selected strains of Bean pod mottle virus.Phytopathology 94: S158.

Table 2. Ground cloth economic threshold for 1st generation beanleaf beetles scouting in soybean (beetles per m2) (Smelser andPedigo 1992, Lam et al. 2000). If the beetle population is higherthan the threshold value, control action should be conducted uponthe emergence of the second generation bean leaf beetles

Marketvalue($/Bu)

Cost of treatment/acre ($/acre)

7 8 10 12 15 18

5.00 5.8 6.7 8.3 10.0 12.5 15.06.00 4.9 5.6 6.9 8.3 10.4 12.58.00 3.7 4.3 5.3 6.4 8.0 9.610.00 2.9 3.4 4.2 5.0 6.3 7.613.00 2.2 2.6 3.2 3.8 4.8 5.815.00 1.9 2.2 2.8 3.3 4.2 5.0

These values were calculated by using the formula: ET � 0.75*EIL. WhereEIL is Economic injury levels. The economic injury levels used here werebased on the work of Smelser and Pedigo (1992), where a beetle feeding onlate season soybean was found to cause an average seed yield reduction of0.000306 kg.

Table 3. Sweep net economic threshold for 1st generation beanleaf beetles in soybean (beetles per 20 sweeps) (Lam et al. 2000). Ifthe beetle population is higher than the threshold value, controlaction should be conducted upon the emergence of the secondgeneration bean leaf beetles

Marketvalue($/bu)

Cost of treatment/acre ($/acre)

7 8 10 12 15 18

5.00 17.4 19.9 24.8 29.8 37.2 44.76.00 14.5 16.6 20.7 24.8 31.0 37.28.00 11.1 12.7 15.9 19.0 23.8 28.510.00 8.8 10.0 12.5 15.0 18.8 22.513.00 6.7 7.6 9.5 11.5 14.3 17.215.00 5.8 6.6 8.3 9.9 12.4 14.9

These values were calculated by using the formula: ET � 0.75*EIL. WhereEIL is Economic injury levels. The economic injury levels used here werebased on the work of Smelser and Pedigo (1992), where a beetle feeding onlate season soybean was found to cause an average seed yield reduction of0.000306 kg.



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Received 14 February 2011; accepted 6 December 2011.



Biology, Yield loss and Control of Sclerotinia Stem Rot of Soybean

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