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Clearing confusion on seed treatments

Over-reliance part of a recurring theme.

November 14, 2007
By Ralph Pearce


40aIn the race to adopt the latest technologies, many farmers have become over-reliant
on various agents for disease, insect and weed control. The scenario has taken
shape in the past decade with Group 2 resistance in weeds. More recently, concerns
have surfaced about the lack of refugia in Bt corn, as well as signs of glyphosate
resistance emerging in the US and migrating north.

Perhaps it is in the interests of avoiding this trend that some in the extension
and agribusiness sectors are voicing concerns about a possible over-reliance
on seed treatments like clothianidin (Poncho). Tracey Baute, field crop entomologist
with the Ontario Ministry of Agriculture, Food and Rural Affairs in Ridgetown,
gave a presentation to farmers during the 2005 Crop Diagnostic Days at Ridgetown
College. Baute's session provided a comparison of clothianidin versus other
seed treatments including imidacloprid (Gaucho) and thiamethoxam (Cruiser/ Helix).

While she acknowledged the benefits these seed treatments provide, she cautioned
that many growers are expecting too much. "Too many people think it's the
silver bullet for everything, and it's not going to be," says Baute, urging
growers to understand what they can and cannot control. "Especially because
all of these new products are the same chemistry, the same family and usually
if one doesn't do it, the other one's going to be the same, as well."


Knowledge always the key
With seed treatments, the key to success is knowing the levels at which insects
can cause damage. For Baute, the message to growers is that just because the
seed has been treated does not guarantee control. In fact, one misconception
is that clothianidin or any of the others can provide 100 percent control. "We
can't get 100 percent control from any product," she says, adding that
the use of these chemistries does not inhibit insects from feeding on treated
seed. "If there's enough insect pressure, then you can't be guaranteed
that plant is going to survive it because enough can take a bite and do enough
injury to kill it. Even if the chemistry finally does kill the insects after
that, the plant may go down still."

Just like detecting soybean aphids or soybean cyst nematode, growers must be
aware of the threshold levels of the insect pests in their fields. "You
don't like to see anything being misused because I would hate for any kind of
resistance to happen," cautions Baute. "We want to be diligent here
and be sure that you have the pest in the first place and then you will see
the most benefit from using a seed treatment."

She takes it one step further, reminding growers that like herbicide chemistries,
there is nothing new coming in the way of pesticides. "Outside of this
neo-nicotinoid group, we need to back off and use it where we need it and ensure
that we get good control," says Baute, noting how difficult it can be now
to find untreated seed.

One myth that Baute has encountered is that use of seed treatments can provide
a yield 'bump', even in the absence of insect pests. Her counter to that is
that it is not a consistent gain and therefore difficult to confirm. In a stressful
situation, she says, it can mimic the effect of a hormonal boost. "We've
learned from the soybean aphid situation that you have to go into your field,
you have to scout, see if the problem's there, and then use the management tools
that will work for you," says Baute.

Early planting also a stress
More than just a problem with over-reliance, Tim Moyes of Bayer CropScience
in Guelph, Ontario, also points to the urgency of early planting as another
factor in the uptake of chemistries like clothianidin. As researchers, extension
personnel and growers have continued to push the limits on early planting, the
need for protection from pests like European chafer or wireworm increases, even
at low populations. "If corn sits in the ground for three weeks, that low
population can do a lot more damage than if it germinates and comes up in five
days," reminds Moyes, who agrees with Baute's concerns of confirming the
existence of insect pests and not over-using the technologies to the point of
resistance. "What we need to do is encourage people to go out there and
actually look."

According to Moyes, there are some standard recommendations on using seed treatments
like clothianidin (Poncho), including sandy soils, a history of corn rootworm
problems or a field that has seen two or more years of hay or alfalfa. In those
fields, wireworm would be the likely pest in subsequent years.

Moyes echoes Baute's advice that growers walk their fields and never assume
they have a particular pest. "If you have never had European chafer, chances
are you don't need to treat for it because they don't just show up," explains
Moyes. "Even the black cutworm problem is really quite sparse, it's on
the north shore of Lake Erie and if you are further north, the odd time you'll
see a black cutworm problem, but most people in this area should not be concerned
about it."

In other words, treat those insect problems that are assured, not assumed.