Are Seed Treatments Enough Control On Corn?
LEXINGTON, KY.
Well over 90 percent of the field corn may
have one of several seed treatments preapplied.
The most common treatments
are those that are applied at concentrations to
control ‘secondary’ pests of corn including wireworms,
white grub, seedcorn maggot, flea beetles,
and seedcorn beetle.
Personally, I don’t like the term ‘secondary’ pest
as when these pests are at high levels and occur
in some fields on a regular basis, they are really
primary pests.
We have two leading seed treatment active ingredients
in corn, clothianidin and thiamethoxan,
they are combined with fungicides
and sold as Poncho and Cruiser and ordered on
the seed. Both of these are in the same chemical
class and have the same mode of action. Both a
systemic and are rapidly absorbed by the seed as
it imbibes water during germination and later
through the roots. Once inside the seedling they
move throughout the plant providing insect protection
above and below ground. While these
seed treatments are similar in many ways there
are also some subtle differences that can affect
performance.
The differences that I’m aware include substantial
differences in solubility in water and
some difference in the spectrum of insects that
they manage. Each of these come in two loading
rates on the seed, a 0.25 mg active ingredient per
kernel and a 1.25 mg active ingredient per kernel.
The higher rate is primarily intended for the
corn rootworm market, the lower rate for the secondary
pests. Research at UK and other universities
has shown that these seed treatments are
able to prevent stand loss and can help to maintain
more uniform vigor during early growth
stages in fields where secondary soil insect pests
are present.
Now the question I ask is, are these seed treatments
providing the level of control that we need?
That is a difficult question to answer as it depends
on the level of particular pests in a given
field. In the vast majority of fields, the secondary
pest is sufficient to control light to moderate levels
of soil insect (excluding corn rootworm). However,
there are certain fields where secondary
pests are found at very high levels and the secondary
rates are not providing enough control.
Our research has shown us that moving to
higher rates of these seed treatments when there
has been a history of high levels of secondary
pests have shown improved levels of control as
measured by improved stands. In a few of these
problematic fields, growers have also combined
seed treatments with low rates of soil applied insecticides
with some success.
There seed treatments are usually found on Bt
corn, CB or RW, or on stacked hybrids. So these
hybrids could have protection from corn borers
(European and southwestern), corn rootworms,
fall armyworm, black cutworm, and those pests
listed at secondary pests.
Can we walk away from these fields and let the
seed treatments and biotech traits manage all of
the insect pests for us? These have been excellent
tools in Kentucky, but I don’t think we
should forget about insect pests during the season.
First, while corn prices remain strong, input
prices have increased dramatically as well. It
would be a huge mistake to let an insect pest get
out of control. The other reason is that we can
see insect pests levels on some occasions that
can overwhelm control tactics. So my recommendation
would be to use seed treatments and
biotech traits as needed based on field history,
planting dates, and other factors that may predispose
fields to higher risk, but do not discontinue
to regularly monitor fields for performance
and insect pests. With high investments and
possibly higher returns on corn, it would be too
expensive to make a mistake by letting a pest
problem get out of control.
The future of seed treatments looks quite promising
with additional active ingredients to control
other pests such as nematodes or even to relive
stress and improve vigor in certain situations.Δ
Dr. Ric Bessin is Extension Entomologist with the
University of Kentucky at Lexington.