Randy wrote:

> So here would be the empirical test:  have any of you seen any groundwater
> tests, or good data on constantly elevating levels in plants?  Some recent
> data that I've seen for canola does not suggest buildup after many years of
> use.  But perhaps it occurs in the heavy clay in Stan's area.
>

Some imidacloprid has now been found in wells in PEI (groundwater).

I have posted data several times from Jim Kemp's unpublished study of
canola in New Brunswick following potatoes, where the level of imidacloprid
in canola the year AFTER potatoes was equivalent to the level of
thiamethoxam in nectar and pollen of the canola (and the canola was seed
treated with thiamethoxam).  But the key factor here is that the potatoes
were soil injected.  That is a much higher application rate per hectare
than seed treatment.  Where canola follows canola the soil residual is
going to be much less.  Thankfully almost no one here soil injects potatoes
any more (too expensive), because set treatment uses so much less product.

I have not seen problems with thiamethoxam, so far, and I have bees in seed
treated canola.  But here that is what they use for the treatment, not
imidacloprid.  The thiamethoxam only controls insects on the canola for
about a month.  Also, here canola does not follow canola;  it is rotated,
often with potatoes, and legally potatoes can only be grown once every
three years here in a particular field.  So, I find it curious that
imidacloprid is the seed treatment used in western Canada, and wonder about
how often canola follows canola there.  I should note that my experience is
only with three canola growers here and they all get their seed from the
same source, so it not much of a sample size.  I had bees in one organic
canola field as a control.   The bees in the organic field actually did
worse over the winter than bees in the treated fields, but I think that was
because they were splits made too late to get much benefit from the bloom
which was already ending by the time I made them, and they would not have
had many foragers until the bloom was totally over.  Those hives were about
the lightest of any in the spring.  So that was not a good control.  But
compared with hives in other non canola yards, the mortality of canola
yards was a bit higher, but not enough to raise warning flags.

In France, sunflowers apparently do follow sunflowers sometimes and the
French apparently did find significant levels of imidacloprid in untreated
sunflowers following seed treated sunflowers.  Maybe Bil Harley will
comment.

Soil injection, which seems the most dangerous application to me (but I
have no experience with chemigation), seems now to be mostly limited to
forestry uses and orchard uses.  But remember, this thread (a long one)
started with Kirk's comment on orange orchard use.

Stan

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