Originating text in English.Citation: Catangui, Michael A.,  South Dakota State University. Cooperative Extension Service. (2002). Soybean aphid in South Dakota.  South Dakota State University, College of Agriculture & Biological Sciences, Cooperative Extension Service, 914, 4-4

Catangui, Michael A.

South Dakota State University. Cooperative Extension Service

K-State Research Exchange

South Dakota Extension Fact Sheet 914December 2002SOUTH DAKOTA STATE UNIVERSITYCollege of Agriculture & Biological SciencesCooperative Extension ServiceUSDAAlthough it is a new pest of soybeans in the U.S., the soybean aphid is commonand widespread in Asia.  Both the soybean aphid (Aphis glycines), and thesoybean plant (Glycine max) are of Asian origin.The first record of soybeans in the U.S. is from 1765 when a seaman brought seedsfrom China via England.  Over two centuries later, in 2000, the soybean aphid wasdetected on U.S. soybeans.  First seen in Wisconsin during summer 2000, theaphid found its way into South Dakota in August 2001.That summer the aphid appeared in three South Dakota counties:  Brookings,Moody, and Minnehaha.  By September 2002, soybean aphids had been confirmedin 20 South Dakota counties (Fig. 1).The soybean aphid is now probably present wherever soybeans are grown in SouthDakota.  South Dakota produces about 145 million bushels of soybeans yearly andcurrently ranks eighth in the top ten soybean-producing states in the U.S.IdentificationThe soybean aphid is currently the only aphid species that infests and multiplies onSouth Dakota soybeans.  It is small but still can be seen with the naked eye.  The wingless form is about1/16 inch long when fully grown and may be yellow to yellow-green in color (Fig. 2).A newborn soybean aphid is about 1/4 the parent’s size.The soybean aphid has two black-tipped “tailpipes” or cornicles that can be seeneasily under a hand lens.  The winged form of the aphid has two pairs of delicatetransparent wings and a general blackish coloration (Fig. 3).  Once on buckthorns,soybean aphids take on a more bluish color but can still be identified by theirblack-tipped “tailpipes” (Fig. 4).Soybean aphids assume several different forms, depending on season and plant con-dition.  Winged aphids are commonly seen in late summer or early spring as aphidsmigrate between soybeans and buckthorns.  Once on a soybean plant, overcrowdingalso may force the soybean aphid to produce winged forms, perhaps to enable it tocolonize other less-infested soybean plants in the field.DayHamlinBrookingsMoodyBrownCampbellLincolnClayUnionTurnerMinnehahaYanktonRobertsMarshallSpinkCodingtonClarkKingsburyMinerMcCookFigure 1.  Distributionof the soybean aphidin South Dakota (as ofSeptember 2002).Michael A. Catangui, Ph.D.Associate Professor/Extension EntomologistPlant Science DepartmentSoybean Aphidin South DakotaPLANT PESTMANAGEMENT IN SOUTH DAKOTAFigure 4.  A wingless soybean aphidon a buckthorn leaf in the spring.Figure 3.  A winged adultsoybean aphid thatmigrated from soybeanto buckthorn in the fall.The two young aphids tothe right will eventuallylay the eggs that willoverwinter on the twigs.Figure 2.  Soybean aphid adults and nymphson a soybean leaf.  Notice the black-tipped“tailpipes” that are characteristic of soybeanaphids in general.MIKE CATANGUIMIKE CATANGUILife CycleThe life cycle of a soybean aphid begins on a buckthorn.  Buckthorns (Rhamnuscathartica) are very common shrubs in the South Dakota landscape (Fig. 5).  Theygrow underneath trees in shelterbelts as shrubs or as small trees along fencelines orfield margins of open fields.  Some homeowners grow buckthorns as ornamental orshelter plants around the house and buildings.Winged female soybean aphids return to buckthorns during the fall to give birth to ageneration of egg-laying wingless females. Male soybean aphids develop on soybeansand fly into the buckthorns in search of the wingless females. The eggs laid besidebuds on the buckthorn twigs survive the winter but the aphids themselves are killedoff by freezing temperatures.  In the spring, the overwintered eggs hatch into nymphs,and after two generations of wingless aphids on buckthorns a generation of wingedfemales migrates from buckthorns to soybeans as soon as the soybeans emerge fromthe soil.Once on soybeans, the winged aphids give birth to numerous wingless female aphidsthat, in turn, give birth to numerous other wingless aphids.  A newborn aphid growsby molting several times and can start bearing live young aphids within a week.Winged aphids are only produced if there is a need for long distance migration suchas when the host soybean plant become overcrowded, or when it is time to go backto buckthorns in the fall.  Soybean aphids can potentially produce 15 generations of aphids on soybeans pergrowing season.InjuryThe soybean aphid has syringe-like mouthparts (Fig. 4) and sucks out the sap ofsoybeans.  Plant injury may be more subtle and harder to detect than injuriescaused by insects with chewing mouthparts, such as grasshoppers and bean leaf bee-tles.  Soybean aphids may be small but when they multiply in large numbers duringthe season, their collective feeding can potentially cause severe damage on soybeans.Sap feeding can cause yellowing, cupping, and wilting of soybean leaves.  Plantgrowth may also be stunted.  Leaf yellowing can be confused with symptoms ofpotassium or iron deficiencies in the soil where the soybeans were planted.Soybean aphids are capable of transmitting mosaic viruses that can cause soybeandiseases, such as soybean mosaic virus, bean yellow mosaic virus, and alfalfa mosaicvirus.  Although able to spread these diseases, however, the soybean aphid currentlyhas not been implicated in transmitting disease-causing viruses in the U.S.  During the 2002 growing season, SDSU research near Beresford indicated that soy-bean fields sprayed for the soybean aphid had yield advantages of between 4 and 11bushels per acre, or 10-27%, over unsprayed soybeans.  However, bean leaf beetleswere also present in the field in addition to the soybean aphids.  It is quite difficultto attribute yield advantages due to control of just one insect.During the 2000 and 2001 growing seasons, some soybean fields in Minnesota andWisconsin were sprayed for soybean aphids and had an average yield advantage of15% (or about 7 bushels per acre) over unsprayed soybeans.ScoutingScouting for soybean aphids should start as soon as the soybean plants produce twotrifoliate leaves (V2)  and be continued until the beginning seed (R5) stage of soybeandevelopment.  Figure 5.  Common buckthorn (Rhamnus cathartica) showingleaves, berries, twigs, and thorn in early fall in South Dakota.Figure 6.  Colony of soybean aphids on a newly-unfurled soybean leaf.Soybean aphids can be found mainly on the young leaves and stems of the soybeanplants early in the season (Figs. 6-7).  As the plants mature, the aphids tend to befound mainly underneath the lower leaves (Fig. 8) and on the developing pods.The presence of numerous ants and lady beetles in the soybean field are signs that soy-bean aphids may also be present.  Ants (Fig. 9) feed on the honeydew excreted by theaphids; lady beetles utilize the aphids as food (Fig. 10).Soybean leaves that look “sticky” or “sooty” are also signs of aphid infestations.  This“look” is possibly due to the honeydew excreted by the aphids as they continuouslyfeed on the soybean sap.As with any insects, the distribution of soybean aphids in the field will not be uniform,and there may be more aphids in the field borders early in the season.  Thus, to esti-mate the average number of aphids per plant, sample the field from the border to themiddle.  Count soybean aphids from at least 10 plants at 10 representative locations in the field(for a total of at least 100 plants inspected).  The entire plant must be examinedbecause the aphids could be in the stems, growing points, flowers, pods, or under-neath the leaves. Economic ThresholdAn average of 200 or more soybean aphids per plant is currently considered economi-cally damaging to soybeans. Soybean aphids can potentially infest any of the growth stages of the soybean plant.However, the plant appears to be most susceptible to soybean aphid injuries if aphidinfestations start early in the vegetative stage (V2) of the plant and continue onthrough the flowering and beginning seed stages (R1-R5) of the soybean.Spraying with an insecticide during the flowering stages of the soybean plant (R1-R2)appears to produce the most benefit or yield advantage, according to early researchfrom states that have already experienced damaging populations of the soybean aphid.However, SDSU research in 2002 revealed that spraying at beginning seed stage (R5)may still result in significant yield advantages if economic numbers of soybean aphidsare present in the field. Spraying too early may result in re-infestation of the sprayed field, while spraying toolate may be unnecessary because the aphid population tends to decline during thepod-fill stages. Natural enemies usually catch up with the aphids later in the season. Because the soybean aphid is a new pest of South Dakota soybeans, there are stillmany variables that need to be investigated before we can fully understand the injuriesthat these insects cause at any given time or plant stage.  Some of these variables aresoybean variety, plant population, row spacing, and  location in the state.  Eventually,soybean aphid management will need to be adjusted for the diverse soybean growingconditions in South Dakota.Figure 7.  Colony of soybean aphids on soybean stem and flower.Figure 8.  Colony of aphids on the underside of a soybean leaf. Figure 9.  An ant tending a soybean aphid. Figure 10.  An Asian lady beetlefeeding on soybean aphids.TERRY MOLENGRAAFTERRY MOLENGRAAFMIKE CATANGUITERRY MOLENGRAAFMIKE CATANGUIMIKE CATANGUIInsecticidesAcknowledgmentsGary Erickson (Brown County agronomy educator), John Gille (Union Countyagronomy educator), and Dr. Walt Riedell (USDA-ARS supervisory plant physiologist)reviewed the manuscript; many thanks.  This publication is made possible throughresearch and Extension funding and a grant from the South Dakota Soybean Researchand Promotion Council. Visit us on the Internet at http://plantsci.sdstate.edu/entReferencesNorth Central Pest Management Center.  2002.  Regional pest alert: soybean aphidAphis glycines Matsumura.  Champaign: University of Illinois.Grau, C., B. Jensen, S. Myers, J. Wedberg.  2002.  Soybean aphid.  Team Grains,Publication 1:1.  Madison: University of Wisconsin Extension.Ostlie, K.  2002.  Managing soybean aphid.  St. Paul: University of MinnesotaExtension Service.General GuidelinesThis publication is intended for use by county Extension educators, pesticide dealers,consultants, commercial applicators, and producers in South Dakota.Recommendations are current at the time of printing.Mention of trade names does not imply endorsement of any product over another ordiscrimination against a similar product.  Always read and follow label directions andprecautions.Most insecticides are capable of causing injury to applicators if not handled properly.Always wear protective gear as specified on the product label. Avoid contact of the insec-ticide with the skin, mouth, nose, eyes, and clothing.  Bathe and wash clothing afterexposure to any insecticides.  Wash clothing on which insecticide residues may haveaccumulated before wearing again.  Wash contaminated clothing separately from otherhousehold laundry.In case of accidental poisoning call: 1-800-222-1222 (Sioux Valley Poison Control Center).Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with theUSDA.  Larry Tidemann, Director of Extension, Associate Dean, College of Agriculture & Biological Sciences, SouthDakota State University, Brookings.  Educational programs and materials offered without regard for race, color,creed, religion, national origin, ancestry, citizenship, age, gender, sexual orientation, disability, or Vietnam EraVeteran status.FS 914:  5,000 copies printed at a cost of __ cents each. December 2002.Insecticides labeled for use against the soybean aphid, Aphis glycines, in South Dakota during the 2003 season. Brand name Active ingredient Product per acre                               Pre-harvest interval (days)   Asana *                    esfenvalerate                5.8-9.6 fluid ounces                     21                          Dimate                     dimethoate    0.5-0.75 pint 21                        Furadan 4 F *            carbofuran       0.5 pint 21                           Lorsban 4E *            chlorpyrifos            1-2 pints                                      28                            Mustang *                zeta-cypermethrin        3.0-4.3 fluid ounces 21    Penncap-M *             methyl parathion           1-3 pints 20                            Pounce 3.2EC *         permethrin                 4-8 fluid ounces 60                            Warrior *                  lambda-cyhalothrin       1.92-3.20 fluid ounces                      45 * A restricted use insecticide.  A valid applicator’s license is required to apply any insecticide (restricted or not) on South Dakota crops.For information on how to obtain an applicator’s license, call the South Dakota Department of Agriculture at (605) 773-3724 or SDSU at (605) 688-4752.

Soybean aphid in South Dakota

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Soybean aphid in South Dakota

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