Ottumwa Courier, IA
07-27-06
Don’t let the crop bugs bite
Bean leaf beetles can be a big problem
By SCOTT NILES Courier staff writer
OTTUMWA — With soybeans reaching the peak of the season, second
generation bean leaf beetles will start appearing, possibly causing damage to
some yields.
Field specialist for the Monroe County Iowa State University Extension
Office Mark Carlton said this might not be a problem this year, but farmers
should stay alert and still sweep their crops often.
He said the first generation of the beetles are just starting to disappear, but they
are not the ones to worry about.
“The first generation of the beetles mainly eat the leaves of the soybeans,” he
said. “It’s the second generation that should be here in about four to five days
that you have to worry about. They are the ones that eat the pods of the plant
and they can spread rapidly and cause significant damage.”
Carlton said with the weather being so good lately and with the sporadic rainfalls
we have been receiving, farmers are in a good spot with yields this year.
Hopes shouldn’t get too high though. The bean leaf beetles can appear at any
time.
If farmers do sweeps, they can cut down on the amount of crops that are lost due
to insects and crop disease, according to Carlton.
He spoke to a group of farmers Thursday night about the diseases and insects
that can plague crops and methods to check for each.
A new technique that he introduced to area farmers, called the “speed sweep,”
could cut down on the amount of time that it takes farmers to check their crops.
It uses a chart of empty boxes. The farmers goes around randomly and checks a
plant and if there are 40 or more spores of aphids on the plant, they put a plus in
the box, otherwise they put a minus.
Depending on how many plus signs are in each row, indicates whether the
farmers need to spray their crops.
Another concept that most farmers around the area seem to be familiar with is
economic thresholds.
Part of the reason the farmers need to count the number of insects or spores on
each plant is to determine the threshold. The threshold is a system devised by
Iowa State University officials that tells a farmer when they need to spray their
crops.
When the amount of pests equals or exceeds the amount of crops that would be
lost because of them, it is time for them to spray.
Depending on how many plants are infected, the farmer can look at the chart and
see how many bugs need to be on the plant before it becomes necessary to
spray insecticides.