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Soybean Aphid Found In North Carolina. John Van Duyn, NCSU Department of Entomology V. G. James Research and Extension Center Plymouth, NC. Soybean Aphid in NC. In September 2005 colonies of soybean aphid, Aphis glycines (SA) were found in NC soybeans by crop consultant Stan Winslow.
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Soybean Aphid Found In North Carolina John Van Duyn, NCSU Department of Entomology V. G. James Research and Extension Center Plymouth, NC
Soybean Aphid in NC • In September 2005 colonies of soybean aphid, Aphis glycines (SA) were found in NC soybeans by crop consultant Stan Winslow. • He first found the pest on beans in a Chesapeake, VA field in early September; this field was sprayed. • Later in September, fields with low levels of SA were found in Gates, Currituck, and Camden counties; populations never reached the treatment threshold. • However, in 2005 many Virginia fields were treated for SA in the Northern Neck and Eastern Shore regions.
Distribution of Soybean Aphid in US • SA was first discovered in MN in 2000; however, a local crop consultant claims to have seen infestations in 1999. • That same year it was also found in Wisconsin, Michigan, Indiana, and Iowa. • Since that time it has spread very rapidly and is now found in all major soybean growing states, as far south as Mississippi and Georgia. Figure 1 shows 2005 distribution of soybean aphid.
Distribution of Soybean Aphid in Asia • SA is widely distributed in eastern Asia (China, Japan, and Southeast Asia to Malaysia and Indonesia). • It has been introduced into Australia. • This wide distribution, from temperate to tropical environments, indicates that it can adapt to most regions of the US. • However, the SA introduced into the US appears to have come from northern latitudes since it uses an alternate host on which to over winter as eggs -- a behavior common to aphids adapted to cold climates.
Identification of Soybean Aphid • SA is a close relative of the cotton aphid, which is commonly found in NC and is familiar to many farmers. • SA is the only aphid found in the US that will develop large colonies on soybean plants. • Adult soybean aphids are generally yellow, have black cornicles (cornicles are tail pipe looking structures at the back of the body), and are approximately 1/16 of an inch long when fully grown. • Young aphids look like adults without wings but are smaller. • Adult aphids may be wingless, or, during periods when they move, develop wings.
Soybean Aphid Biology • Eggs hatch in spring to produce winged females. • Early season SA don/t mate and move on winds. • They move to soybean fields and begin laying living young (not eggs). • New aphids are sexually mature in 3-7 days and new progeny will begin reproducing in 5 days. • SA may infest “V” stage soybeans and remain in the crop into the late reproductive period. • Later in the season males appear, due to plant chemical and photoperiod changes, develop wings, mate with females and move. • Adults females lay eggs on several species of buckthorn bushes for over-wintering; southern adapted populations in Asia may be active all year.
Damage & Virus Transmission • SA sucks sap (phloem) from soybean plants and cause plant stress. • Excess sap sugars are excreted by the SA as a liquid aphid called “honeydew”. • On “V” stage plants aphids are only a threat under very high populations. • “R” stage soybeans are more sensitive to aphid damage, particularly in early reproductive stages (e.g. R1 – R3); very high numbers of SA are capable of causing significant growth reduction, distorted foliage, and lower seed yields. • Wang et al. (1996) in China found that soybean yields were reduced by 27.8% and plant height decreased by ca. 8 inches-6.
Damage & Virus Transmission • Insecticide spray tests in the US have shown yield increases ranging from 10% to 20%, depending on aphid population density, product used, and other plant stresses. • SA is a known vector of a number of plant virus diseases. • E.G., some domestic viruses spread by SA include alfalfa mosaic virus, soybean mosaic virus, and bean yellow mosaic virus.
Scouting and Thresholds • In the mid-west, scouting is achieved by examining plants for signs of aphids (e.g. disfigured leaves, ants on plants, cast aphid skins, honeydew on leaves) and aphids in plant terminals. • Scouting begins in mid-vegetative stages and continues to R5 (seeds forming in pods); it is done weekly. • Aphids are estimated on the leaves and an average of five samplings is compared to a threshold of 250 aphids per terminal leaf.
47 aphids/leaf 11 aphids/leaf 82 aphids/leaf Soybean aphids on soybean leaves at 3 below threshold levels.
An above threshold soybean aphid infestation (about 150 showing).
An above threshold infestation; about 300 showing on this leaf.
Biological Control • NC entomologists recommend biological control for cotton aphid management. • The same approach will reduce populations of SA. • Parasitic wasps, insect predators, and a parasitic fungal pathogen of aphids can exert a powerful influence to keep aphids in check. • Basically, all the farmer has to do is to avoid disrupting the field, by spraying insecticides at the wrong time. • Most spraying for corn earworm and other insects occurs after plants pass the aphid sensitive stages and will likely not conflict with aphid management.
Upper – lady beetle adults and larva. Lower – dead aphids (brown puffed-up aphids) killed by a wasp parasite.
Soybean Aphid Insecticides • Soybean aphid is sensitive to a number of insecticides labeled for soybean in NC. • Several pyrethroid insecticides that are popular with farmers, for corn earworm control, will work on aphids and are labeled for aphids. • Several phosphate insecticides are also available. • Products labeled on soybean for soybean aphid control include: Asana XL, Baythroid 2, Lorsban 4E, Mustang Max, Penncap-M, and Warrior.
Will Soybean Aphid Become An Important Pest In NC Soybeans? • SA is northern-adapted and relies upon an alternate over-wintering host, the buckthorn bush. • In NC, the soybean aphid will have trouble surviving winter in substantial numbers due to the relative low number of buckthorn plants. • This suggests that SA will have to travel into NC, in high numbers, to infest vegetative stage soybeans to damage “R” beans. • This possible but unlikely, if fields are not disrupted. • Until SA adapts develops an over-wintering behavior that doesn’t require buckthorn bushes, SA will likely remain as a minor pest. • When this happens, soybean aphid on soybeans may be much like cotton aphid on cotton --- that is, a somewhat frequent pest.
Acknowledgement • Information and pictures for this presentation were gathered from the following sources: • Soybean Aphid in Iowa – 2005. by M. E. Rice and P. Pedersen, Iowa State University; (http://www.extension.iastate.edu/Publications/SP247.pdf); • Soybean Aphid in Nebraska. by Tom Hunt, University of Nebraska. (http://entomology.unl.edu/fldcrops/soybean_aphid04.htm); • Soybean Aphid. Plant Health Initiative, NCSRP (http://www.planthealth.info/diag_photo_dp.htm); • Minnesota Soybean Production, Soybean Aphid. by Ken Ostlie, University of Minnesota. (http://www.soybeans.umn.edu/crop/insects/aphid/aphid.htm) • Soybean Aphid. Center for Regulatory and Environmental Information Systems. (http://ceris.purdue.edu/napis/pests/saphid/index.html)
