I’ve heard reports that soybean aphids
are appearing in South Dakota and western Minnesota currently.
With the intermittent southern winds and warm weather we have
experienced in June and early July, it’s not surprising to hear these reports.
A few things come to mind regarding soybean aphids…
First, “scout and
treat” is the best action by farm managers and field agronomists. Aphids do not like temps above 90F, but there
has been high humidity. Economic treatment
threshold is 250 aphids/plant on greater than 80% of the soybean plants. Here is a great resource by the Univ. of MN
Extension on the topic: https://extension.umn.edu/soybean-pest-management/scouting-soybean-aphid
Second, even though we haven’t sprayed
for soybean aphids in a couple years, will the aphids remember they were
resistant to some pyrethroid insecticide compounds back in 2017? Well, the NDSU entomologist team found a few
aphids in Grand Forks County in the summer of 2019 and tested that exact
theory.
From NDSU:
“These aphids were then sent to Dr. Koch’s laboratory at the University of
Minnesota for rearing and testing for pyrethroid resistance. Results indicate
that this population was fairly resistant to bifenthrin (trade name Brigade 2EC,
Capture EC, and generics) with 60-70% survivorship, and two of the four
lambda-cyhalothrin (Warrior II and generics) vials had single survivors while
one had 50% survivorship. So, pyrethroid resistant soybean aphid populations
may be established in ND or migrating into ND from other resistant areas.” Source: NDSU Crop and Pest Report – Aug 29,
2019
I guess it does make sense… Do short height parents tend
to have short children? Yes, and
therefore pyrethroid resistant soybean aphids from 2017 will continue to be
present if/when we should have to implement control measures again.
For more insight
on management of resistant soybeans, please see this link: https://www.ag.ndsu.edu/publications/crops/management-of-insecticide-resistant-soybean-aphids
Lastly, what are
a couple sound insecticide recommendations for a solution if the aphids build
to treatment levels?
Lorsban™ (chlorpyrifos) will be a common treatment option. However, Lorsban™ has been used extensively in the past against soybean aphids and resistance to chlorpyrifos is most likely building in our region as well and we could easily see less than desirable results soon with the product.
Lorsban™ (chlorpyrifos) will be a common treatment option. However, Lorsban™ has been used extensively in the past against soybean aphids and resistance to chlorpyrifos is most likely building in our region as well and we could easily see less than desirable results soon with the product.
Cobalt™ Advanced
from Corteva® will also be widely recommended, but please remember that Cobalt™
is a pre-mix of Lorsban™ and Warrior II™.
With aphid resistance probably building to Lorsban™ and already present
in Warrior™, will Cobalt™ give us the control levels we need? Maybe, maybe not.
There is one insecticide
with a different mode of action (Group 4C) on the market labeled for soybean
aphids that is also safe on beneficial insects that are predatory on the
soybean aphids (primarily speaking of the lacewings and lady bug larvae). Transform™ WG is systemic within the plant’s
xylem and very effective on soybean aphids.
The Tansform™ should cost a bit less per acre versus Lorsban™ or Cobalt™,
and the respray potential on a field application of Transform™ will be very low
as the beneficial insects should keep any new infestations of aphids to a very
manageable number. Transform works a bit
slower for a complete aphid kill, but it will be a sound alternative.
To view the Transform™ WG label: https://www.corteva.com.au/content/dam/dpagco/corteva/au/au/en/products/files/Transform-WG-Isoclast-active-Insecticide-Label.pdf
To view the Cobalt™ Advanced label: https://www.corteva.com.au/content/dam/dpagco/corteva/au/au/en/products/files/LINK_LABEL_Cobalt_advanced.pdf
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