Zero Tolerance For Pigweed Weed Species
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[July 26, 2019]
When it comes to keeping pigweed in check,
scientists across the Corn Belt, including Dr. Aaron Hager,
Associate Professor, Department of Crop Sciences, University of
Illinois, are recommending "zero" tolerance for palmer amaranth
This is due to the fact that one female plant will produce
460,000 seeds. To put this into prospective consider the fact
that even if 95% of the seeds produced are controlled, there is
still the potential for 23,000 plants to survive.
Two particularly troublesome pigweeds are Tall Waterhemp and
Palmer Amaranth, which have and are continuing to develop
resistance to herbicides. In Illinois, Tall Waterhemp is
resistant to 6 different classes of herbicides and Palmer
Amaranth is resistant to 3. If that is not bad enough, members
of the pigweed or amaranth family can cross pollinate between
species which aids in the rapid spread of resistance as well.
A weed free field is the key starting point to managing the
situation. Tillage or an herbicide burndown plus a residual
herbicide are essential when Palmer weed is present. This must
be followed by vigilant scouting and herbicide applications
combining post-emergence and residual products when new
seedlings are identified.
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If Palmer is identified after it is too big for
herbicide control, hand removal is the best option. Any field in
which Palmer weed reaches maturity should be harvested last and left
untilled. Deeply burying the seed may lead to a decade of Palmer
problems as future tillage brings old seeds up to the surface.
However, leaving any seed on the surface will allow for natural
forces to reduce the viability of seed and help reduce germination
the following spring, and burndown herbicides can be applied to
reduce the population potential. Research shows that viable seeds
left near the surface will "burn out" in about 4 years if no future
seeds are added to the seed bank.
[Doug Gucker, Local Food Systems and
Small Farms Educator, University of Illinois Extension]