"The
culprit can be one of any three herbicides which have been approved for use on
pastures and forage crops,” said David Trinklein, University of Missouri
Extension horticulture specialist.
Newer
versions of herbicides with active ingredients such as clopyralid, picloram and
aminopyralid can pass through the digestive systems of foraging animals and
arrive, unchanged, in the manure. If that manure is composted, farmers could
unwittingly introduce these plant-killing compounds into their soil, Trinklein
said.
“My
first encounter with this was with a gentleman in northwestern Missouri who was
using buffalo manure for composting,” Trinklein said. “We were able to
demonstrate, on tomato, that there was something in the compost.”
So
why not just test compost before selling it? Commercial testing for these
chemicals is costly.
“The
test is between $300 and $400 per chemical,” Trinklein said. “Say you test for picloram
and it’s not found in the sample. You’ll have to spend another $400 to test for
another chemical. You would have to keep testing until you find the culprit.
Meanwhile, you’ve spent $400 a test.”
It’s
not just compost. These herbicides can show up in mulch too.
“Let’s
say a farmer put up hay but it got wet. Normally that would be great for
mulch,” Trinklein said. “But if that hay had been treated with picloram, avoid
using it since there is the potential for the herbicide to leach into the soil and
harm plants.”
Once
these herbicides have been added to the soil, through compost or mulch, there
aren’t many options for correcting the problem. You can remove and replace the
soil, but that is expensive, labor-intensive and time-consuming.
You
also have the option to wait until soil microbes break down the herbicides
naturally, but these new-generation herbicides have lengthy half –lives of
months to years.
“These
herbicides, ultimately, will break down, but it might take a couple of years,
depending on the concentration,” Trinklein said. “We would hope that in most
cases we could plant the following year, but one may want to avoid
herbicide-sensitive plants, such as tomato.”
The
good news is there’s a simple and inexpensive way to test for these compounds.
Take green bean seeds and plant them into the compost.
“Green
beans are very sensitive to herbicide,” Trinklein said. “If the seedlings come
up okay, the compost is good. If they come up twisted and damaged, allow the
compost to age until the herbicide is broken down.”
It
is important not to panic. “We don’t want to dissuade people from using compost
and organic matter,” Trinklein said. “They’re the gardener’s best friend when
it comes to building healthy soil. Farmers and gardeners should find out whether the
compost supplier has used animal manure, and if so, make sure the animals have
not been fed forages sprayed with these herbicides.”
In
this situation, being informed and proactive is your best defense. Farmers should use the green bean test before they
work compost into the soil. Also, talk with your compost supplier. Make sure
they’re aware of the problem and discuss the steps they are taking to avoid it.
(by Debbie Johnson, MU Writer)
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