Producers know how challenging it can be to manage weeds. Faced with that same age-old challenge, Swedish organic farmer Jonas Carlsson began looking for ways to reduce weed infestations in his crops, especially thistles in spring wheat. Noticing that broadleaf weeds had a stiffer and thicker stem while the crop was soft and vegetative, Carlsson started thinking about how he could use those differences to his advantage. He came up with a unique solution -- a giant comb with stationary knives, in a technique called combcutting, which can selectively cut off or severely damage broadleaf weeds in the understory of a small grain crop without harming the crop or disturbing the soil.
When a small grain crop like wheat, oat, barley or rye is in the vegetative growth stage and prior to stem development, the crop’s leaves are flexible. Broadleaf weeds like Canada thistle growing within the vegetative cash crop generally have a stem, which continues to grow thicker and stiffer as the weed matures. Combcutting technology uses a series of stationary knives that are set at a specific angle and distance from each other. As the implement is lowered into the plant canopy and the tractor drives forward at a speed between six and nine miles per hour, the knives comb through the cash-crop understory, allowing the crop leaves to pass between the knives unharmed, whereas the stem of the weed is cut off or severely damaged. Cutting off the weed in the understory doesn’t kill the weed like an herbicide, but it does put the weed at a competitive disadvantage against a taller cash crop and reduces future weed seed production.
To prevent buildup of weeds on the knives, a rotating brush constantly clears the knives so they can continue cutting weeds. To be the most effective, there must be a physical difference between the crop and the weed – timing is the most important factor. The weed must be stiffer, thicker, have a different branching pattern or be higher than the crop.
After the cash crop has matured beyond the vegetative stage, combcutting can no longer be used within the crop canopy. But it can be used to cut weeds above the mature cash crop to reduce the weed seed population. That has been done with lentils to further reduce weed seeds of thistle, wild oat and wild mustard. Common weeds that can be clipped combcutting are wild mustard, pigweed, lambsquarters and thistle.
For organic growers, combcutting can reduce weed competition and plant stress for a small grain crop without using tillage for weed control, which also brings up more weed seeds. For non-organic growers that technology can greatly reduce or eliminate herbicidal applications as well as provide several other benefits.
• reduce costs overall when compared to the expense of herbicide applications
• work around herbicide-resistant weeds
• facilitate market access for a crop that hasn’t had herbicides applied to it
Combcutting isn’t the whole solution for reducing weeds in a small grain crop. Rather, the technology should be used in combination with other recommended good soil health management practices.
• proper seeding rate
• diverse crop rotation with as many crop types as possible to feed soil life and break pest cycles
• diverse cover crop mixes comprised of several plant families and functional groups to provide continuous living roots and appropriate soil cover outside the cash crop growing period
• minimal soil disturbance through reduced tillage or no-till
• integration of livestock on cropland with proper grazing management of diverse cover crop mixes where possible
This blog is produced by the National Center for Appropriate Technology through the National Sustainable Agriculture Information Service, under a cooperative agreement with the U.S. Department of Agriculture’s Rural Development.
Justin Morris is a regenerative livestock specialist for the National Center for Appropriate Technology. Visit attra.ncat.org for more information.