Preventing weed seed dissemination
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.