While engaging in an online debate around genetically modified organisms, I realized that few non-farmers understood the issues farmers have dealing with weeds.
Many people are ready to condemn herbicide-resistant crops and the application of herbicides and seem to see this as a frivolous activity by farmers.
I suggested they not do any weed control in their garden and wait until the end of the season to observe the results. The smart ones would have told me they mulch to control weeds. However, mulching a thousand acres of canola or wheat is not feasible.
Mulching on a small scale for weed control can work because it smothers weed seedlings that may be produced by the seed bank.
All cultivated fields have thousands of seeds of various species in their seed bank. This arises by virtue of the characteristic of weeds because they have evolved to produce thousands of seeds each generation, and they produce seeds that have various levels of dormancy, some of which may not germinate for a decade or more.
Soil tillage brings up weed seeds from the seed bank, allowing them to germinate. A farmer can reduce, but not eliminate, the impact of weeds from the seed bank through a year of fallow or a cover crop but such techniques take the land out of production for the year.
Changes to prairie agriculture since the 1970s to significantly reduce tillage not only help to maintain our soil but also minimize soil disturbance and disturbance of the seed bank.
Unlike natural ecosystems, in which plants come into a balance with other plants, fungi, insects and animals, cropping systems are an unnatural system. They are continuously threatened by the evolutionary tactics of weeds, diseases and insects, which reduce yield and/or quality.
Weed control will always be with us in large-scale agriculture, most critically before the weeds draw on soil nutrients or water needed by the crop. Our use of herbicides has much improved since they were first used in the 1940s and will continue to improve as new technologies come along. Hopefully, with greater understanding through genomic technologies of our crops and weeds, more elegant solutions will come along.
At present, herbicide-resistant crops through genetic modification provide an elegant solution to the seed bank problem and offer the best means we currently have to control weeds in large-scale agriculture.
Graham Scoles is a plant scientist at the University of Saskatchewan’s agriculture college.