Transcript Soybean Aphid Found In North Carolina

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.
FIGURE 1.
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.
Adult soybean aphid (wingless)
Soybean aphid colony showing immature aphids
Colonizing adult (with wings) and new progeny
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.
Soybean aphid and eggs on a buckthorn bush stem.
Buckthorn bush, soybean aphid’s over-wintering host.
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.
Soybean aphid on vegetative plants.
Soybean aphid on reproductive plants and curled leaves.
Photo 8. Soybean aphid damage to leaves.
Soybeans infested with soybean aphid.
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
Soybean aphids on soybean leaves at 3 below threshold
levels.
82 aphids/leaf
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 overwintering 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.ht
m)
– Soybean Aphid. Center for Regulatory and Environmental
Information Systems.
(http://ceris.purdue.edu/napis/pests/saphid/index.html)
THE END
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