Agri News, MN
07-03-07
Farmers urged to scout fields for soybean aphids
By Jean Caspers-Simmet
Agri News staff writer
NASHUA, Iowa -- Farmers got some hands-on experience scouting for soybean aphid during
last week's Northeast Research Farm's field day.
Iowa State University Extension soybean entomologist Matt O'Neal coaxed farmers into a
soybean field to look for aphids, and they found some.
If farmers see ants and ladybird beetles, otherwise known as lady bugs, aphids are likely to be
feeding, O'Neal said. The Nashua research farm has a 25-foot-tall soybean aphid suction trap
that monitors aphids May through October. Thirty traps throughout the Midwest provide an
early warning system.
Aphids have been detected throughout the state this summer, but not at threshold levels. An
insecticide would kill the aphids but also kill beneficial insects that eat aphids. Farmers who
tank mix an insecticide when they spray their glyphosate as a preventative treatment against
aphids are wasting their money, and could make things worse if there is a high infestation of
aphids later this season, O'Neal cautioned.
O'Neal told farmers that when they scout, they need to get in the field and look beyond the top
couple of leaves on plants. Aphids often feed under the canopy, on the bottom side of leaves
and along stems.
While farmers were able to find a hot spot in the field where there were several plants that
likely had 500 aphids per plant, the field was nowhere near threshold, which is 80 percent of
plants infested with 250 aphids per plant.
Researchers are anticipating that aphid numbers could be similar to 2005, when the threshold
was reached in late July, O'Neal said. He's urging farmers to start scouting weekly, and he
outlined a speed scouting method. Each plant that has more than 40 aphids is considered a
plus. Plants with less than 40 are a minus. If 11 plants are pluses, the field is likely at
threshold. O'Neal suggested farmers speed scout in four or five areas of a field. More
information and a practice video game on speed scouting are available at
www.soybeanaphid.info.