Both organic and non-organic farmers are looking for new ways to control weeds. Non-organic farmers need to control herbicide-resistant weeds, and many organic farmers are seeking ways to control weeds with less tillage or within the constraints of perennial crops.
New tools are needed even though the overall approach of organic agriculture helps prevent serious weed problems. For example, a well-designed crop rotation inhibits weeds, as do cover crops and mulch. Also, organic nutrient management helps control weeds when nutrient inputs, such as compost, provide a slow nutrient release that benefits crops more than weeds.
Researchers with the Organic Science Cluster 4 (OSC4) are investigating novel approaches to weed control including:
- Electrical weed control
- Bioherbicides
- Cover crop mulch
- Improving crop vigour
The research is being conducted across Canada on crops as diverse as cranberries, dry beans and cereals.
Electrical weed control
A new way of controlling weeds is by electrocuting or zapping weeds. When electrical current passes through plant tissue, it’s transformed into heat, which causes liquid to vaporize. The resulting pressure build-up causes cells to burst throughout the plant. The result ranges from suppression of growth to plant death.
Electrical current affects crops as well as weeds. Consequently, this form of weed control is most effective when crops and weeds are separated by space or time, for example, weeds between crop rows or weeds above the crop canopy. Electrical weeders have been used for field crops (primarily for above-canopy weeds), horticultural crops, vineyards and orchards.[1]
Several electrical weeders are commercially available. Brand names include the Lightning Weeder©, Weed Zapper©, XPower©, RootWave©, and NUCROP©. Most are designed to be used on tractors either front-mounted or as pull-behind units (some as part of robotic weeding systems), although RootWave© is a hand-held unit intended for spot weeding. NUCROP© has a two-step approach involving spraying plants with a conductive liquid before applying the electric charge.
Electrical weeders can be custom built. For example, Japanese researchers electrified two stainless steel nets using a solar cell-driven pulse-type negative voltage generator (the type used for strong electric fences).[2] This could kill weed seedlings in a fallow bed or before crop emergence.
Potential disadvantages for electrical weeding include the risk of injury to the operator and fire. Also, the current can potentially damage soil life. One study found that electrical current negatively affected earthworms and other soil life, however this was based on using electrical current intensively to desiccate forage, not control weeds.[3] Other studies found no significant effect of electrical weeding on soil life.[4] There is, however, indisputable evidence of the negative effect of tillage on soil micro- and macro-organisms.
Two OSC4 research activities are trialling electrical weeders. Dr. Yosra Menchari (Université Laval) is using a custom-built electrical weeder on cranberries in Quebec. Drs. Robert Nurse and Jamie Larsen (AAFC Harrow Research and Development Centre) are using the Weed Zapper© for mid- to late-season weed control in dry beans in Ontario. (They are also looking at the use of the Weed Zapper© for pre-harvest crop desiccation.)
Bioherbicides
Bioherbicides impair plant growth or kill plants through substances derived from organisms.[5] Farmers might be familiar with the practice of using allelopathic cover crops, such as cereal rye, to control weeds. Both the living and dead rye can inhibit germination of other plants. Bioherbicides derived from essential oils or phytotoxic chemicals from plants, such as neem, cinnamon or mustard, can provide this same function but in a much more targeted way.
Many bioherbicides contain microorganisms that transmit disease to plants. For example, Sarritor™ is derived from Sclerotinia minor and used to control broadleaf weeds.[6]
Other bioherbicides contain byproducts from processing plants into food, feed or fuel. For example, distillers’ dried grains with solubles is a byproduct of ethanol production, corn gluten meal is from wet-milling corn, and mustard seed meal is derived from pressing mustard seeds into oil[7].
Broad-spectrum bioherbicides affect a great variety of plants, whereas the specific ones (often derived from microorganisms) just target certain species. Depending on the type of bioherbicide, application method, and target plant, the effects can range from inhibiting germination to killing plants. In general, bioherbicide residue breaks down quickly once applied and has minimal effects on other life forms.[8]
Dr. Menchari is exploring the efficacy of two bioherbicides on weeds in cranberries. BioLink® Herbicide EC contains caprylic and capric acids, which are derived from coconut oil and palm seed kernels.[9] She is also assessing the BELOUKHA® Agricultural Herbicide containing pelargonic acid, derived from the essential oil of Pelargonium (geranium).[10]
Cover crop mulch
Cover crops have long been used to control weeds through competition and sometimes allelopathic chemicals as described above. Another traditional weed control method is using mulch, such as straw, to reduce the amount of sunlight available to weeds.
Farmers and researchers have been experimenting with ways to improve the weed suppressive effects of cover crops and mulch by using a roller-crimper. This heavy drum with dull blades rolls over the cover crop and leaves it lying flat, while the blades kill plants by crimping their stems. The cash crop is then planted directly into the mulch.
This form of weed control has many potential benefits. The soil is covered by the cover crop in the winter and by mulch the following summer. The roller-crimper terminates the cover crop without tillage. Unlike tillage that can negatively affect soil quality and soil life, the mulch improves soil quality and provides habitat for soil organisms, in addition to controlling weeds (particularly early-season weeds).
Tillage also releases carbon dioxide from repeated passes by the tractors and by stimulating carbon loss from the soil. In contrast, the cover crop can sequester (trap) carbon dioxide and increase levels of soil organic matter.
Beyond the environmental benefits of the roller-crimper, farmers can save money compared to controlling weeds with tillage. A study comparing these two systems in organic soybeans found the organic no-till approach using cereal rye terminated by a roller crimper “generated ~19% greater net revenue across the study period” (no-till vs tillage = US $845 vs US $711 per hectare).[11]
Drs. Nurse and Larsen are using this system to control weeds in dry beans. They seed cereal rye in the fall and terminate it at the early-milk stage the following spring using a roller-crimper. Then they seed dry beans into the mulch. The researchers are also investigating the effect of his mulch on Sclerotinia white mould (other studies have found that rye mulch reduces Sclerotinia in soybeans and dry beans).[12]
In Alberta, Dr. Hiroshi Kubota (Lacombe Research and Development Centre) is exploring different ways to control weeds and provide fertility. His team is looking at three four-year grain crop rotations. The rotations differ in how the cover crops are terminated – first option tillage, second option mowing or crimping, and third option grazing.
For the second option, red clover is overwintered and then terminated at the flowering stage by a roller-crimper or mower. The following crop is seeded into the mulch.
The third option, grazing green manures, has potential to mitigate the greenhouse gas (GHG) emissions released by livestock by reducing the GHG emissions from tillage and sequestering carbon. At the same time, grazing can improve soil fertility and the ‘tools’ responsible for mowing and terminating the cover crop can be sold as organic meat. A mix of orchardgrass and red clover is grazed by cattle in its second and third year. At the end of year three, the livestock will be grazed intensively enough so the plants won’t overwinter. The following spring, wheat will be seeded.
Researchers will compare the overall success of the three systems, as well as GHG emissions, carbon sequestration, changes in soil fertility, and weed control.
Improving crop vigour
Weed management is often viewed as harming the weeds. Another approach is to improve the competitiveness of the crop. This can be accomplished by:
- Cultivar selection – choose competitive varieties well suited to growing conditions (climate, soil, farming methods). In the OSC4 dry bean and cranberry studies, researchers are comparing the competitiveness (and other traits) of various cultivars.
- Timing and density of seeding – seed crops when conditions are ideal for rapid emergence. High plant density can help crops outcompete weeds but can also lead to more fungal problems. This balance is being evaluated in the dry bean research.
- Stimulants – apply substances to alter crop growth. Dr. Menchari’s team is exploring the use of GroSpurtTM WS-40, a product made from the plant growth regulator gibberellic acid. This may lead to more plentiful and longer runners, which increase the competitiveness of the cranberries. The team is also comparing various biostimulants (e.g. Bacillus spp) which could potentially stimulate root and shoot growth, and enhance nutrient absorption, thereby giving the cranberries an advantage over the weeds.
Weed control is an evolving field. As the OSC4 results emerge, we will learn more about these novel ways to control weeds. To follow the researchers’ progress, visit the research activity webpages:
Dr. Yosra Menchari – Cranberries
References
[1] A comprehensive review of the subject can be found at https://www.cambridge.org/core/journals/weed-science/article/exploring-the-potential-of-electric-weed-control-a-review . (See also Micro Electric Shocks Control Broadleaved and Grass Weeds and The impact of electrocution treatments on weed control and weed seed viability in soybean | Weed Technology | Cambridge Core.)
[2] Use of a Pair of Pulse-Charged Grounded Metal Nets as an Electrostatic Soil Cover for Eradicating Weed Seedlings
[3] Field fodder conversion using electricity – Negative effects on earthworms and changes in labile carbon fractions – ScienceDirect
[4]https://www.cambridge.org/core/journals/weed-science/article/exploring-the-potential-of-electric-weed-control-a-review ,
[5] Comprehensive reviews of the subject can be found at Bioherbicides: An Eco-Friendly Tool for Sustainable Weed Management – PMC , Bioherbicides in Organic Horticulture, and Bioherbicides: Dead in the water? A review of the existing products for integrated weed management – ScienceDirect .
[6] The Bioherbicide Approach to Weed Control Using Plant Pathogens – ScienceDirect
[7] Bioherbicides: An Eco-Friendly Tool for Sustainable Weed Management – PMC
[8] Unlocking the potential of bioherbicides for sustainable and environment friendly weed management – ScienceDirect
[9] Rapid Burndown: Caprylic and Capric Acid for Weed Management in Organic Vegetable and Specialty Crop Production | eOrganic
[10] Assessing Herbicide Efficacy of Pelargonic Acid on Several Weed Species
[11]Cover crop management strategies affect weeds and profitability of organic no-till soybean | Renewable Agriculture and Food Systems | Cambridge Core
[12]https://www.cambridge.org/core/journals/renewable-agriculture-and-food-systems/article/abs/rolledcrimped-cereal-rye-residue-suppresses-white-mold-in-notill-soybean-and-dry-bean/8F9999CDF83856AE9E147BC32CF377E6
Published June 4, 2025
Organic Science Cluster 4 is an industry-led research and development endeavour co-managed by the Organic Federation of Canada and the Organic Agriculture Centre of Canada at Dalhousie University and supported by the AgriScience Program under Agriculture and Agri-Food Canada’s Sustainable Canadian Agricultural Partnership together with over 80 funding partners.
