Des Moines, Iowa
May 29, 2007
If past history is any indication
of soybean aphid pressure to be seen in 2007 - be prepared. Not
only are soybean aphids more predominate during odd years, but
counts of aphids overwintering this year were high, indicating
this could be a banner year for soybean aphids.
“Illinois and Minnesota reported particularly high counts of
overwintering soybean aphid,” says Travis Kriegshauser,
Pioneer Hi-Bred International,
Inc., senior research associate in Waterloo, Iowa. “At this
point, it is important to prepare for the possibility of
significant soybean aphid populations and anticipate the need to
scout for this pest beginning in late June through August.”
To aid in monitoring this pest, a number of state university Web
sites and the U.S. Department of Agriculture track the movement
of aphids. Growers can monitor sites such as
http://www.sbrusa.net
(select soybean aphid in the upper right-hand corner drop-down
menu), and begin scouting when aphids appear in their area.
Identifying soybean aphids
Soybean aphids are small and yellow with distinct black
cornicles (“tailpipes”). At only one-sixteenth inch long (the
size of a pinhead or smaller), they cannot be distinguished from
other aphids with the naked eye. The soybean aphid is the only
aphid in North America known to extensively colonize in soybean
fields.
Soybean aphids overwinter as eggs on a woody shrub species known
as buckthorn. The eggs hatch in the spring into wingless types,
which establish on buckthorn for two generations. The third
generation emerges, produces wings and migrates to soybean
fields and other acceptable hosts.
“The soybean aphid can produce up to 15 generations during the
summer on soybeans before migrating back to buckthorn in the
fall as winged females,” says Kriegshauser. “Once on buckthorn,
the winged females give birth to wingless females, which mate
with males developed on soybeans to produce the overwintering
eggs.”
Management options
Kriegshauser notes that soybean fields in areas where aphids
were detected the previous year are at greatest risk. The
northern states bordering the Great Lakes have the highest
annual probability of aphid infestations.
“Management decisions regarding soybean aphids are difficult due
to the explosive potential of aphid populations and the
interaction of aphids with climatic conditions and natural
predators,” says Kriegshauser.
Scout carefully to determine if treatment is needed, and time
insecticide treatments to maximize their effectiveness. Economic
threshold guidelines are currently established at 250 aphids per
plant.
“Scout at least 80 percent of the field,” says Kriegshauser.
“Select 20 to 30 plants in 10 random areas of the field. If you
count 250 or more aphids per plant and populations are on the
increase, it’s time to spray.”
Pioneer, in collaboration with Kansas State University, also has
developed a technique for screening soybean lines for their
ability to naturally reduce the rate of growth, survival and
reproduction of soybean aphids that feed on soybean plants.
“This type of resistance is called antibiosis,” says
Kriegshauser. “Pioneer has characterized current soybean
varieties for their aphid antibiosis. The next step is to
identify sources of exceptional antibiosis and incorporate this
trait into other varieties.”
Today, aphid antibiosis ratings can be used as a management tool
to help in determining field scouting priorities and insecticide
application decisions.
For more information about scouting for soybean aphids, contact
your local Pioneer sales professional or a Pioneer agronomist.
Pioneer Hi-Bred International, Inc., a subsidiary of DuPont,
is the world’s leading source of customized solutions for
farmers, livestock producers and grain and oilseed processors.
With headquarters in Des Moines, Iowa, Pioneer provides access
to advanced plant genetics in nearly 70 countries. DuPont is a
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DuPont puts science to work by creating sustainable solutions
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