Evaluation of reduced-risk weed management approaches for annual grass control in sweet corn

Project code PRR07-040

Project lead Robert Nurse - Agriculture and Agri-Food Canada

Objective

To investigate the use of a living-mulch cover crop as a weed control approach for sweet corn; to evaluate the potential environmental and economic benefits of the weed management system; and to communicate the findings of the study

Results Summary

Background

Sweet corn is the most extensively planted vegetable crop in Canada, and weed management, traditionally achieved through the use of cultivation and herbicide treatments, is a costly component of sweet corn production. Growing a cover crop as "living mulch" between rows of sweet corn can be an alternative to conventional cultivation and herbicide practices, providing protection against soil erosion and compaction, while also suppressing weeds.

The key people who will benefit from the information collected in the present study are Canadian sweet corn growers. The adoption of suitable treatments from this study could reduce pesticide use and costs, and improve environmental safety.

Approaches

Research trials were conducted from 2007 to 2009 to evaluate the effectiveness of several living mulches for management of annual grasses in sweet corn. The three living mulches evaluated were adzuki beans, fall rye (spring seeded), and oilseed radish, alone or in combination with a herbicide, and compared with a weed-free industry standard control. The adzuki beans were paired with s-metolachlor + linuron pre-emergence (PRE); the fall rye was paired with saflufenacil PRE; and the oilseed radish was paired with pendimethalin PRE. A weed-free control (industry standard) was established by applying s-metolachlor/atrazine PRE fb nicosulfuron + Agral 90 post-emergence. An additional comparison was made using all of the herbicides applied to the sweet corn without the living mulch. Trials were established in two key sweet corn regions in Canada, Ontario and Quebec, with two locations chosen in Ontario to represent different crop heat units and soil types.

Results

In 2007, living mulches were seeded at the same time as the corn, leading to a high degree of interspecific competition and unacceptable yields. The 2007 data were therefore discarded from the study. This issue was rectified in 2008 by over-seeding the living mulch at the 5-leaf stage of the corn, which corresponds to the end of the critical weed-free period.

When seeded alone and with no herbicide, the three living mulches were effective in reducing the biomass of all weed species in the study in comparison to an untreated control, but not in comparison to the industry standard or the herbicides. The best living mulch options for weed management in the absence of a herbicide were spring-seeded fall rye and oilseed radish. When living mulches were paired with a herbicide, adzuki beans were the most effective living mulch. Overall sweet corn yields with the use of living mulches were comparable to the herbicide only treatments or the industry standard.

Pairing a herbicide program with a living mulch helped lower the environmental impact of the management system by approximately 50%. While the living mulch systems alone exhibited reduced weed control in comparison to the industry standard, they still produced equivalent yields and could therefore represent a pesticide-free option for growers.

This study showed that spring-seeded fall rye and oilseed radish may be good candidates for living mulch weed control, even without the use of a herbicide. This could lead to substantial pesticide reduction in sweet corn systems. Furthermore, adzuki beans significantly reduced annual grass biomass when paired with an herbicide. Future work will need to focus on optimal living mulch rates in combination with reduced herbicide rates.

Results of the study were disseminated through various means, including a series of field tours, a presentation at the Canadian Weed Science Society Meeting and a poster at the Ontario Fruit and Vegetable Convention.

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