How do you get rid of Canada Thistle in an organic system?
Thanks for the email and the tough question. Perennial weeds
are the hardest to remove from fields organically. In many
cases, they are there because of past practices based on chemical
herbicides that worked well to eliminate pressure from annual
weeds but open the door for perennials to move in and take
hold. Of the perennial weeds, Canada thistle is one of the
toughest. Crop rotations that favor row crops where cultivation
can rip them out, and hay or forages where cutting and chopping
can weaken their roots can help. Small grains can be a nightmare,
because there are few opportunities to have any meaningful
If the problem is serious, you may need to take more drastic
steps and actually take the area out of production for a year
and use more intensive management strategies. We have found
that a system of rotating rye and buckwheat has had the best
success. We start by planting rye in the fall after your crops
are harvested. Then, in the spring—as early as possible—till
in the rye and plant buckwheat, till in the buckwheat once
it begins to bloom and plant buckwheat again, repeat again
with buckwheat if possible, then plant rye again in the fall.
By the following spring, you should see a great improvement.
The constant tillage and planting of cover crops weakens the
root system of the thistle plants. This system seems to work,
although you will loose production of marketable crops for
one season while you spent 18 months on the program.
Good luck and let us know how it works.