OSCII Activity C.37

New innovative weed management for organic crops

Activity summary

There is a need for more effective weed management in organic crop production utilizing biological and lower-risk products. Only a limited number of products are currently acceptable in organic agriculture and some have limited efficacy. Currently approved products have no systemic activity, no soil activity or persistence and have no pre-emergence activity on weeds.

The possibilities of using manuka oil as a natural herbicide have been reported. Distilled from the manuka tree, this essential oil showed good results in field tests conducted against weeds as both a preemergent and postemergent herbicide. Manuka oil has a number of important weed control properties that currently-approved products do not have. Manuka oil’s level of soil activity is superior to all other currently available essential oils, commercialized for organic weed control. Soil persistence of manuka oil opens up a multitude of new possibilities for its use as a tool for weed management in organic agriculture and may be a potential bridge between traditional and organic agriculture. Manuka oil is also readily taken up by roots and translocated to the foliage where it results in the bleaching of the green tissues. Therefore, regrowth of the surviving plants is not an issue with this essential oil. Manuka oil also has shown synergy or additive efficacy when tank-mixed with other currently approved essential oils.  No other essential oil currently in commercial use for weed control has shown such strong activity on weeds. The systemic activity of manuka oil addresses many of the major limitations normally associated with currently approved natural herbicides. The prospect of developing manuka oil as a novel natural herbicide with soil activity is especially attractive. Manuka oil addresses many of the major limitations normally associated with currently-approved organic herbicides.

This project will evaluate manuka oil on selected broadleaf and grass weeds for its effect on weed control and determine its PRE and POST activity and its synergy/additive effects with other new and currently approved organic weed control products. Manuka oil will be applied prior to planting or crop emergence and directed postemergence alone or tank mixed with other essential oils, at various concentrations. The potential for selective broadleaf weed and grass control will also be investigated by manipulating the timing of application or placement of material and by exploiting differences in the tolerance of the crop and the target weed.

This project will provide weed control efficacy and crop safety data on improved biological, lower-risk herbicides to support minor-use submissions to the Pest Management Regulatory Agency (PMRA) that are appropriate for use by organic growers. This research will lead to novel uses of bioactive natural products and provide organic growers and the public with environmentally and economically sustainable alternatives to synthetic chemical herbicides. This represents an important step in fulfilling society’s desire for reduced dependence on synthetic chemical inputs. It will also serve as an important component for integrated pest management systems for organic agriculture. An integrated approach is the foundation of successful weed management. Improved weed management for organic farming will help growers to seize opportunities, reduce imports and respond to the growing demand for organic food. It will help growers to find solutions to the long standing issue of managing weeds in organic crop production. Developing new natural weed control products with superior weed management properties to control or effectively suppress weeds will help the organic crop production industry remain competitive and sustainable into the future. 

Materials and Results to Date

Activity researchers

Name Affiliation
Rene Van Acker, Activity Leader University of Guelph
Robert Grohs University of Guelph
John O'Sullivan University of Guelph
Rachel Riddle University of Guelph


Activity graduate students

Sierra Harris