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Aphid Season
Around The Corner?
Soybean aphid infestations in recent years indicate that
growers across much of the bean belt should be prepared for managing the
menacing pests. A complete integrated pest management program should be
considered if infestations attack your farm.
This aphid has been confirmed by USDA in Delaware, Georgia, Illinois,
Indiana, Iowa, Kansas, Kentucky, Michigan, Minnesota, Mississippi,
Missouri, Nebraska, New York, North Dakota, Ohio, Pennsylvania, South
Dakota, Tennessee, West Virginia and Wisconsin and in the Canadian
provinces of Quebec, Ontario and Manitoba.
This newsletter will hopefully help you better understand the threat
aphids present, how to spot them on time and how to control them before
the damage is done.
Plant Injury,
Yield Loss Can Result
Iowa State University (ISU) entomologists point out that
soybean aphids may be small, but when they multiply in large numbers
during the season, their collective feeding can cause severe damage to
soybeans.
Plant injury may be more subtle and harder to detect than injuries
caused by insects with chewing mouthparts, like grasshoppers and bean
leaf beetles. The aphid has syringe-like mouthparts that suck the sap
out of soybeans. They cause damage directly by sucking plant sap and
transmitting viruses and indirectly by creating an environment for sooty
mold that will reduce photosynthesis.
ISU entomologists say symptoms of direct feeding damage may include
plant stunting, pod and flower abortion, reduced seed size and seed
counts and puckering and yellowing of leaves. They colonize tender
leaves and branches as early as the seedling stage. Later as the growing
point slows, the aphids slow their reproductive rate, move down to the
middle and lower part of the plant and feed on the undersides of leaves,
stems and pods.
Yield loss caused by aphids is variable, and it can be influenced by
many factors. Entomologists say those factors include aphid numbers,
virus transmission, weather, natural enemies and variety selection.
On-farm strip trials from Iowa have showed up to 18-bu./acre yield
differences between an insecticide-treated strip and a non-sprayed strip
in an aphid-infested field. Reports from other states have been as high
as 25-bu./acre yield losses from soybean aphids. Aphids have no apparent
effect on oil or protein content of the soybeans.
Also, remember that soybean aphids are capable of transmitting viruses
that can cause soybean diseases, such as soybean mosaic virus (SMV) and
alfalfa mosaic virus (AMV). ISU entomologists say the role of soybean
aphid in the transmission of soybean virus is not well understood.
Source: Iowa State University
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Aphid-Resistant
Varieties Are Coming - But Not A Silver Bullet
The North Central Soybean Research Program (NCSRP) has
been working on development of soybean varieties that have resistance to
soybean aphid. Funded by state and national soybean checkoff programs,
resistant varieties could be a strong tool in the attack on aphids. But
researchers say good scouting and a solid insecticide program will
likely still be needed.
“We’re screening different lines from several university breeding
programs,” says Kelly Tillmon, entomologist at South Dakota State
University. “We test them on small plots in multiple states, with
varying growing conditions and varying levels of aphids and monitor
aphid population growth and yield on the different lines.”
Those tier I lines are examined and the better looking ones move to the
tier II stage, according to NCSRP, in which lines are tested in more
typical growing conditions. From those can emerge new aphid biotypes
with some ability to break host-plant resistance. A biotype 1 was
captured in 2006, says Glen Hartman, University of Illinois/USDA-ARS.
“What we don’t know is how predominate the biotype 1 is or how
widely dispersed it is.” This biotype shows ability to overcome a
source of resistance known as Rag 1.
Matt O’Neal, Iowa State University entomologist, says there are three
lines of resistance. One is Antixenosis, a term that describes an insect
that doesn’t attach itself to a plant. O’Neal says the aphid “may
not recognize the plant or sometimes it might be that the plant has very
hairy leaves.”
Antibiosis is a second type of resistance, in which aphids feed, but
feeding interferes with reproduction, adds Dechun Wang, Michigan State
University plant breeder. A third form of resistance is tolerance, says
O’Neal, where a plant has a lot of aphids feeding on it, but doesn’t
show yield decreases.”
Wang says it’s not known how many biotypes are in the U.S., but that
there are different aphids in different locations. He says aphids have
likely not managed to overcome resistance “since we haven’t had a
resistant variety available commercially yet.” But nature’s ability
to overcome resistance is one reason NCSRP has so many biotypes in the
pipeline.
O’Neal says that if the aphid can overcome some source of resistance
that comes out of the research, it isn’t a complete loss. He says
growers should scout and consider an insecticide program if aphid
populations go above the 250 threshold, even on resistant plants.
“The frequency of spraying will drop, and growers will be able to use
less insecticide,” he says. “But you can’t just plant
aphid-resistant soybeans and walk away. You don’t want one hammer for
aphids. You want a lot of hammers.”
Source: North Central Soybean Research Program
Small Investments To
Battle Soybean Pest Paying Off Big
 The small amount of money put toward fighting the tiny yet
destructive soybean aphid will pay big dividends in the coming years,
thanks to a research and outreach system developed during the last 50
years, says Michigan State University (MSU) Economist Scott Swinton.
State and federal governments have spent $17 million on soybean aphid
research and education since 2003. The net economic benefit of that
integrated pest management work, or IPM, should reach $1.3 billion
during the next 15 years, an annual rate of return of 180%, says
Swinton.
“This is an example of what a good payoff you can get as a result of
long-term research,” he says. “There’s been a half-century of
research into IPM. In the process a lot of techniques were developed and
lots of understanding was gained about the relationships between crop
and pest life cycles, infestations and the weather to decide when it’s
necessary to control them without wasting money and creating health
risks.”
IPM takes a comprehensive approach to pest management that balances
economics with environmental and human safety, as well as with what
makes sense on the ground in the local community, says Michael Brewer,
MSU’s IPM program coordinator.
Controls, which might include chemical and biological methods, are only
put into action once a carefully determined cost-effectiveness threshold
is crossed. Fewer than 250 aphids/plant, for example, probably won’t
impact soybean yield and early use of insecticides could actually kill
beneficial insects such as parasitic wasps.
“For me it’s almost like having a good national defense system in
case you’re attacked in a time of war,” says Swinton. “Having a
good IPM research and outreach system enables you to respond rapidly to
invasive species like the soybean aphid.”
Soybeans are the second-largest cash crop in the U.S., exceeding 3
billion bushels in 2005 with sales of $17 billion. Two-thirds of the
crop goes to poultry, pig and cattle feed, and about a third is
exported, according to government figures.
Soybean fields were nearly insecticide-free in the Midwest until just
five or 10 years ago, when aphids began to appear in north-central
states. By 2005, 22% of soybean acreage nationally was being treated for
the sap-sucking pests, which stunt plant growth and transmit viruses.
Michigan’s acreage treatment rate rose to 42% by then, and
Minnesota’s to 56%, says Swinton.
He and doctoral student Feng Song measured the cost of state and federal
soybean aphid research and outreach programs since they began in 2003,
and calculated the net benefits to growers and consumers during the next
15 years. Their projection of $1.3 billion in savings was the result.
USDA Soybean Aphid
Spraying Recommendations
R1 to R5 growth stages
During the period when the soybean crop is reproductive, an insecticide
application may be necessary when there are 250+ aphids/plant and
approximately 80% of the field is infested and populations are
increasing. Sequential scouting in the same field is necessary to
determine if populations are increasing.
R6 growth stage
A higher threshold is required for economic return during the R6 growth
stage. If treatment options are considered, ensure preharvest intervals
of the insecticidal product chosen are met prior to application.
R7 growth stage and later
During the R7 and R8 growth stages, there is no economic return on
insecticidal applications.
Check Out These
Soybean Aphid Web Sites
USDA Aphid Site – sba.ipmpipe.org/cgi-bin/sbr/public.cgi?host=All%20Legumes/Kudzu&pest=soybean_aphid.
North Central Soybean Research Program Updates – www.planthealth.info/aphids_basics.htm.
North Central Regional Soybean Aphid Suction Trap Network – www.ncipmc.org/traps/index.cfm.
University of Illinois –
www.ipm.uiuc.edu/fieldcrops/insects/soybean_aphids/index.html.
Iowa State University – www.ent.iastate.edu/soybeanaphid/.
Kansas State University – www.oznet.ksu.edu/entomology/extension/InsectInfo/SoybeanAphid.htm.
Michigan State University – www.ipm.msu.edu/soybean/aphid.htm.
North Dakota State University – www.ag.ndsu.nodak.edu/aginfo/entomology/entupdates/Soybean_Aphid/sybn_aphd.htm.
Ohio State University – ipm.osu.edu/soyaphid/index.htm.
Penn State University – www.ento.psu.edu/extension/factsheets/soybeanAphid.htm.
University of Kentucky – www.uky.edu/Ag/IPMPrinceton/SoybeanAphid/sbaphidindex.htm.
University of Minnesota – www.soybeans.umn.edu/crop/insects/aphid/aphid.htm.
University of Wisconsin – www.plantpath.wisc.edu/soyhealth/aglycine.htm.
Virginia Tech University – www.idlab.ento.vt.edu/.
Thanks For Viewing
Again, thanks for taking time to read this e-newsletter.
Hopefully it has helped answer some of your questions on soybean aphids.
If you have a particular question you’d like to see answered in our
next issue scheduled for early April, contact your Aphid Alert editor at
beef2lar@suddenlink.net.
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