Crop Insurance Today Third Quarter 2020 - 15

Once in the stem, the larvae feed on stem
tissue that supplies water and nutrients from the
soil to the top of the plant. In mild cases yield is
lost, plants show signs of wilting, and the stem
is weakened and becomes susceptible to breakover. In other cases, soybean plants wilt and die.
"In 2019, it was 21 days after adult emergence
that we noticed wilting. I think the time period
was similar again this year," Justin said.
Once the larvae enter the soybean stem,
they are protected because contact insecticides
cannot reach the larvae. Thus, at this stage of
development, controlling Soybean Gall Midge
is difficult. Pesticide researchers are examining a number of strategies relating to timing,
rates, periodicity, and chemistry. As of now, the
only recommendation is to target adults with
pyrethroid chemistries with residual activity
before they lay eggs. While seed treatments
may offer some protection, these insecticides
and over-the-top applications of contact insecticides cannot offer enough residual protection
because the adult emergence and egg laying
window is too wide and is getting wider than
in 2019.
Last year, researchers opined that if soybean
planting was delayed, farmers might miss the
adult emergence window. In 2019, an average of
16 days of emergence was recorded at a given site.
"We blew that away this year," Justin said.
"If emergence from overwintering sites stops
now (mid-July) we will have an average of 26.5
days with the longest at 34 days-far longer
than 2019."

As such, even soybean planted at the end of
June are still at risk.
Justin is confident that fields that held Soybean Gall Midge the previous year are a source
for the insect the following year. And, in 2020,
insect emergence from this year's soybean started
before emergence had even completed from last
year's soybean fields.
"This overlapping emergence of prior year's
and current year's generations complicates the
problem by allowing last year's Gall Midge to
exchange genetic information (through breeding) with this year's, and by simply extending the
emergence window," Justin said.
Two additional hosts have been identified for
Soybean Gall Midge that occur in perennial herbaceous vegetation in field borders and ditches.
These observations have led to some thinking
that mowing grassy borders may reduce damage;
however, researchers have not fully tested this hypothesis, so it is not currently a recommendation.
Fortunately, damage is limited to field edges
so far. But damage caused by Soybean Gall Midge
has resulted in 100 percent yield loss in heavily
infested areas up to 100 feet from the field edge,
and losses up to 20 percent at greater distances.
Narrow fields are at risk for even greater losses
because a larger area of the field is on the edges. In 2019, Iowa State University Extension and
Outreach reported that a farmer with an infested
field had yields ranging from 4.3 to 43.9 bushels per acre. That same field typically yielded 70
bushels per acre. Losses of this magnitude are
attention grabbing.

Recently Justin spent several weekends in July
traveling through eastern Nebraska looking for
the insects. On one of those days he stopped at
34 randomly selected soybean fields and found
the Midge in every field. Although visible damage was not apparent at every site, Justin was surprised by how prevalent the Midge has become.
He plans to travel south and randomly check soybean fields along the Kansas border to get a grasp
on the regional extent of infestations in 2020.
Farmers are hopeful that, as researcher learn
more about the insect, a containment strategy
will be found soon. As mentioned, this pest was
not really causing much damage a few years ago.
But Soybean Gall Midge is becoming more prevalent, and along with that will come yield loss.
While losses can be indemnified under a Federal
crop insurance policy, developing good farming
practices to deal with this pest is troublesome. As
mentioned, a few insecticides offer some level of
control, but multiple applications are hampered
by re-entry restrictions and may be too costly
anyway. Interestingly, hail damage does create infection sites and is linked to the presence of Soybean Gall Midge. A graduate student researcher
working with Justin will conduct research this fall
to determine if damaged soybean elicit a chemical cue that attracts the Midge. Further, Justin
and colleagues are conducting management
studies this year to see if they can find strategies
that can reduce the impact of this insect.
"There are early signs of progress; however,
we will need to wait for yields to determine their
value," cautioned Justin.

Extensive damage to field edges is common. Although this area is not large, the midge will overwinter in this field and be a source of emerging
adults next year.
CROPINSURANCE TODAY®

15



Crop Insurance Today Third Quarter 2020

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https://www.nxtbook.com/allen/cint/55-1
https://www.nxtbook.com/allen/cint/54-4
https://www.nxtbook.com/allen/cint/54-3
https://www.nxtbook.com/allen/cint/54-2
https://www.nxtbook.com/allen/cint/54-1
https://www.nxtbook.com/allen/cint/53-4
https://www.nxtbook.com/allen/cint/53-03
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https://www.nxtbook.com/allen/cint/52-04
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https://www.nxtbook.com/allen/cint/52-02
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http://www.brightcopy.net/allen/cint/51-04
http://www.brightcopy.net/allen/cint/51-03
http://www.brightcopy.net/allen/cint/51-02
http://www.brightcopy.net/allen/cint/51-01
http://www.brightcopy.net/allen/cint/50-04
http://www.brightcopy.net/allen/cint/50-3
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http://www.brightcopy.net/allen/cint/50-1
http://www.brightcopy.net/allen/cint/49-4
http://www.brightcopy.net/allen/cint/49-3
http://www.brightcopy.net/allen/cint/may2016
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http://www.brightcopy.net/allen/cint/november2015
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https://www.nxtbook.com/allen/cint/november2013
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https://www.nxtbook.com/allen/cint/november2012
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https://www.nxtbook.com/allen/cint/44-4
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