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Re: Atrazine!

Theresa Mau-Crimmins wrote:
> 
> Hello fellow prairie enthusiasts,
> I am a grad student at Western Michigan University.  Quite recently,
> folks here have begun tossing around the idea of a prairie restoration
> on our campus of about 50 acres--yippie!!!  We've been putting together
> species lists, burning regimes, and coming up with all sorts of research
> projects.  The administration is very anxious to get something planted
> on this open area that for the past many years has been farmed.  The
> original plan was to seed it this fall.  Trouble is, we just discovered
> that it was treated with Atrazine last spring.  We've been doing some
> research on this troublesome chemical, and it seems that it breaks down
> in about 2 years or so on the surface, but leaches down and takes much
> longer to break down at deeper levels of soil.  How have you who have
> done restorations/plantings dealt with this?  Can we go ahead and plant
> this coming spring, and then hope that the Atrazine will break down
> quickly enough that by the time our forbs' roots reach down that far,
> they will not be affected?  We'd greatly appreciate advice from folks
> who've dealt with this specifically for prairie plants.
> 
> Thanks much,
> Theresa Mau-Crimmins
> x93mau@wmich.edu
> 
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You should not experience any problems with atrazine assuming that last
spring meant spring of 1998.  Even if atrazine had been applied in
spring of 1999 I would not expect problems with injury except in areas
where the sprayer overlapped the spray pattern when it turned and made
the subsequent pass causing a double rate to be applied in that area.
Atrazine was at one time labeled for weed control in the establishment
of many of the native warm season grasses.  Atrazine will however injure
or kill many forbs.  It was used only for native grass establishment to
be used for pasture or hay fields.  It would not be suitable for praire
restoration where forbs are going to planted with the native grasses. 
Furthermore not all native grasses are tolerant so this chemical would
limit diverse grass seed mixures.  It is no longer labeled for this
purpose because the market for this use would not support the
registration costs that would have to be incurred by the manufacturer. 
Atrazine controls some grass weeds e.g. foxtails and many broadleaves
e.g cocklebur, ragweeds, etc.  Atrazine is used for weed control in
corn.  Farmers who use it limit the rate applied because they do not
want carryover into the season following corn because most farmers grow
crops like soybeans after corn and soybeans are injured by atrazine
carry over.  Atrazine is used only about half as much as it was several
years ago because of water quality concerns and carry over into
susceptible rotational crops like alfalfa, soybeans, dry beans, sugar
beets etc.  In fact it is no longer legal to apply atrazine at rates per
acre that was used on fields growing continuous corn several years ago. 
Most of the corn belt cropland has corn and soybeans growing in
alternate years so herbicides that have long half lives cannot be used. 
To make a short story long, I would not be concerned about your
plantings this fall.  There is one way to if you have carryover by using
a bioassay method.  It is real simple.  Obtain a sample of soil from the
treated area and a sample of soil from the untreated area.  It is
critically important to make sure that the soil is the same in both
areas.  Plant some forb seed in flower pots potted with treated soil in
one set of pots and untreated soil in other pots.  Use the same species
and number of seeds in both treatments.  Water as you need to and
observe the plant growth in each set of pots.  If atrazine residues are
still present I would expect the forbs to be injured and plants growing
in nontreated soil to grow normally.  Use more than one species of forbs
because we really don't know about the tolerance of some to these
species to the chemical.  If you select a species that is tolerant then
your bioassay will be meaningless.  You may want to use soybeans or
another indicator species known to be susceptible to atrazine.


Brett Roberts
Illinois State Conservation Agronomist
USDA-NRCS

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