Basics on Organic & Conventional Weed Control

Basics on Organic & Conventional Weed Control presented by James Quinn

James Quinn is the Horticulture Specialist for the University of Missouri Extension’s Central Region. Before moving to Missouri he was a wholesale producer in Michigan, growing salad greens and herbs. On Saturday, he presented on the basics of both organic and conventional weed control.

Organic weed control requires the combination of several methods, including: prevention, cover cropping, flame weeding, cultivation, crop rotation, mulching, mowing, and fostering biological diversity. No single method can provide complete pest control, but together these methods can create an environment where pest pressures do not affect crop yields. Flame weeding is an interesting method that involves carrying or wheeling a flame torch that kills weeds with heat. Flaming can be used to produce a stale seedbed by flaming the freshly seeded bed before the crop emerges. This method can be expensive, but it does provide efficient weed control for small-scale organic growers.

Another organic method of weed control is mulching. Both synthetic and organic-based mulches are available for the organic grower. The only stipulation with a synthetic mulch is that it must be removed at the end of the season in order to meet organic certification standards. Both types of mulches can smother weeds and lower the soil temperature, but organic mulches can contribute to soil organic matter. Synthetic mulches also have the possibility of raising soil temperature if that would be advantageous (e.g. black plastic). Organic herbicides are an option for the organic grower, as long as they are approved by your organic certifier—and it is always good to double-check. It is important to note, however, that these organic herbicides are usually not as potent as conventional herbicides.

In the world of conventional weed control, glyphosate (the active ingredient of Roundup) is the most widely used herbicide. Reasons why glyphosate is so widely used are that it is simple, allowed for use on all vegetables, can be combined with other herbicides, and has a short preharvest interval. Some problems with glyphosate are that it does not inhibit new weed emergence and some weeds have developed resistance to the chemical. The use of a single herbicide for weed management can lead to the development of herbicide-resistant weeds. Because of this, it is good to only spray when necessary and rely on a variety of herbicides to control weeds on your farm.

Other conventional herbicides in use for vegetable production are Dual II Magnum, Command, Atrazine, and Bicep for preplant applications; and Sandea, Poast, Select, Impact, Callisto, and 2,4-D for postemergent applications. In some cases there is a drift hazard, so it is very important to know the safety hazards for any herbicide you may use. It is also effective to couple these herbicides with plastic mulch to create a very repressive weed control strategy.
(by Luke Freeman Senior at the University of Missouri, majoring in Sustainable Agriculture.)