Preventing weed seed dissemination
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happened to notice driving around this week several unused nursery liner
fields that contained numerous weed species close to flowering and seed
set. In particular, marestail or horseweed (Conyza canadensis)
is a winter/summer annual that produces several thousand seeds per
plant. Each seed is equipped with small hairs or pappus that allows it
to be transported long distances with the wind.
Several options are available for weeds such as marestail including
mowing, chemical control or tillage. Mowing or tillage will destroy most
of the above-ground stems or roots and prevent seed production. The
drawbacks to frequent tillage include bringing new weed seed to the
surface, cost of the tillage equipment and operation, and soil
structural problems. Mowing will prevent seed set and spread without
disturbing the soil. Of course, herbicides also remain an option, but
with the occurrence of glyphosate resistance in marestail in other
neighboring states, it is important to rotate your modes of action to
minimize resistance. For example, tank mixing Lontrel (clopyralid) with
glyphosate would give you two modes of action and give better control of
larger maretail plants. Scouting and preventing weed seed dissemination
on your nursery is an important proactive measure that should be
included in your weed control programs.
