soybeanaphid06

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Published on March 27, 2008

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Slide1:  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:  Soybean aphid in NC In September 2005, colonies of soybean aphid, Aphis glycines, 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 soybean aphid were found in Camden, Currituck, and Gates counties (northeastern NC); populations never reached 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:  Distribution of Soybean Aphid in US Soybean aphid 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. Slide4:  FIGURE 1. Distribution of Soybean Aphid in Asia:  Distribution of Soybean Aphid in Asia Soybean aphid 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 soybean aphid 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:  Identification of Soybean Aphid Soybean aphid is a close relative of the cotton aphid, that is commonly found in NC and is familiar to many farmers. Soybean aphid 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. Slide7:  Adult soybean aphid (wingless) Slide8:  Soybean aphid colony showing immature aphids Slide9:  Colonizing adult (with wings) and new progeny Soybean Aphid Biology:  Soybean Aphid Biology Eggs hatch in spring to produce winged females. Early season soybean aphids do not mate. 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. Soybean aphid may infest vegatative 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. Slide11:  Soybean aphid and eggs on a buckthorn bush stem. Slide12:  Buckthorn bush, soybean aphid’s over-wintering host. Damage & Virus Transmission :  Damage & Virus Transmission Soybean aphid sucks sap from soybean plants and cause plant stress. Excess sap sugars are excreted by the aphid as a liquid 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 are capable of causing significant growth reduction, distorted foliage, and lower seed yields. Wang et al. (1996) in China found yields reductions of 27.8% and plant height decreased by ca. 8 inches-6 if plants were heavily infested. Damage & Virus Transmission:  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. Soybean aphid is a known vector of a number of plant virus diseases. For example some domestic viruses vecean aphid include alfalfa mosaic virus, soybean mosaic virus, and bean yellow mosaic virus. Slide15:  Soybean aphid on vegetative plants. Slide16:  Soybean aphid on reproductive plants and curled leaves. Slide17:  Soybean aphid damage to leaves. Slide18:  Soybeans infested with soybean aphid. Scouting and Thresholds:  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 R4 (seeds 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. Slide20:  11 aphids/leaf 47 aphids/leaf 82 aphids/leaf Soybean aphids at 3 below threshold levels. Slide21:  An above threshold soybean aphid infestation (about 150 showing). Slide22:  An above threshold infestation; ca. 300 showing on this leaf. Biological Control :  Biological Control NC entomologists recommend biological control for cotton aphid management. The same approach will reduce populations soybean aphid. 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. Slide24:  Upper – lady beetle adults and larva. Lower – dead aphids (brown puffed-up aphids) killed by a wasp parasite. Soybean Aphid Insecticides:  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? :  Will Soybean Aphid Become An Important Pest In NC Soybeans? SA is northern-adapted and relies on 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 the aphid will have to travel into NC, in high numbers, to infest vegetative stage soybeans in order to damage reproductive stage beans. This is possible but unlikely, if fields are not disrupted. Until soybean aphid adapts and develops an over-wintering behavior that doesn’t require buckthorn bushes, it 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:  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) Slide28:  THE END Slide29:  Questions ?

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