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March 12, 2008
by Ric Bessin,
Kentucky Pest News #1154
Well over 90% of the field corn may have one of several seed
treatments pre-applied. 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 thiamethoxam; 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 pest 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 |
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