Field vegetable production: Using cover crops for weed management

Introduction

Weed management is an important crop protection component in vegetable production. Non-chemical weed control options are needed to help growers reduce reliance on herbicides and risk of resistance development. Cover crops (CC) have been identified as an approach to sustainable weed management.

Cover crops serve important functions such as enriching soil organic matter, cycling nutrients, and protecting soil from water and wind erosion. Cover crops have also been used as part of an integrated weed management approach. However, information on CC approaches, applications and benefits pertinent to vegetable crops grown in Canada is not readily available. Therefore, a literature review was conducted to determine the feasibility of using CC in field vegetable production systems as part of integrated weed management practices to minimize the use of herbicides.

Methodology

Published scientific literature and extension articles on CC research for key vegetable crops (potato, sweet corn, field tomato, carrot, onion, Brassica crops, peas, cucurbit crops, green and wax beans, and lettuce) in North America and other regions with similar climates in Europe were reviewed. From this review, approaches which can be adopted for weed management in field vegetable production in Canada were identified based on:

1. Economics
2. Potential to suppress weeds by allelopathy (inhibition of growth of a plant by a toxin released from a nearby plant of the same or another species)
3. Amount of research that has been conducted for the system in temperate regions
4. Environmental impact

Economics included establishment costs, impact on crop yield, and potential for the CC to add value via control of weeds (for example reduced herbicide input cost), via control of other pests (for example increased yield or reduced input cost of other pesticides) or as a product such as forage.

Results

Potential to adopt CC to reduce herbicide use in vegetables has been demonstrated mostly by studies conducted in the United States (US). There are few scientific studies on CC for weed control in vegetables from Europe or Canada. Full season weed control by CC was rare in the literature. Some additional weed control is usually required later in the season.

Cover crops can lessen herbicide use by:

• Reducing the number of pre-plant or pre-emerge (PRE) applications;
• Switching from broadcast to band application; and,
• Switching from PRE to post-emerge (POST) applications as needed.

Switching to POST usually involves herbicides that are less persistant in the environment than PRE. Savings in herbicide cost compensates the CC cost in some studies but not others. There is wide variability between studies and systems in degree of weed control, crop response and costs. Some systems add value beyond weed control, thereby increasing profitability.

Species of weeds controlled varies widely between and within systems. In general, annuals, and not biennials or perennials are suppressed by CC. Allelopathy is a promising mechanism of control, and is likely to work best where weeds are small seeded, and the crop is not. Rye residues are allelopathic with better efficacy against annual dicots than grasses and have consistently controlled lambsquarters, nightshade, plantain, goosegrass and barnyardgrass. Brassica residues are also allelopathic, depending on stage, and notably provide control of crabgrass and pigweed. Smother crops such as sorghum or sudangrass can provide control of perennials such as quackgrass during growth, but at the expense of about half of the growing season. Sorghum residues also have allelopathic effects, controlling pigweed, barnyard grass and others.

Recommended approaches

Conclusions

Growers are encouraged to trial rye/vetch mixture prior to tomato or rye before cucurbits with minimum or no till planting, or cereal rye overseeded into late harvested crops, or sorghum before late planted or after early harvested vegetable crops. Adoption of these recommended approaches will likely lead to reduced use of herbicides, hence reduced risk from pesticides, better resistance risk management and other economical and environmental benefits.

If using any of these approaches, note:

• Vetch should be planted by September. If available water is limited, it is advisable to burndown the rye or rye/vetch mixture in spring before it uses too much moisture. A tank mix may be needed to kill vetch; in this case, a minimum of two weeks is needed before transplanting the new crop. Reducing nitrogen fertilizer rate to subsequent vegetable according to vetch growth is also advisable.
• Mowing the CC may enhance weed control.
• Row cleaners, also called trash whippers, mounted on seeding equipment can improve crop stands when seeding through CC residues.
• Herbicide requirement will be reduced according to amount of mulch left by the CC, existing weed pressure and the weather - spray as needed.

References

• Abdul-Baki, A.A., J.R. Teasdale, R. Korcak, D.J. Chitwood, and R.N. Huettel. 1996. Fresh-market tomato production in a low-input alternative system using cover-crop mulch. Hortsci. 31:65-69.
• Abdul-Baki, A., and J.R. Teasdale. 2007. Sustainable Production of Fresh-Market Tomatoes and Other Vegetables With Cover Crop Mulches. Farmers Bulletin, 2280 United States Department of Agriculture.
• Ball-Coelho, B., A.J. Bruin, R.C. Roy, and E. Riga. 2003. Forage pearl millet and marigold as rotation crops for biological control of root-lesion nematodes in potato. Agron J. 95:282-292.
• Ball-Coelho, B., A.J. Bruin, R.C. Roy, and A.J. Bruin. 2005. Long-term effects of late-summer overseeding on corn grain yield and nitrogen balance. Can. J. Pl. Sci. 85:543-554.
• Burgos, N.R., R.E. Talbert, and K.I. Yong. 2006. Grass-legume mixed cover crops for weed managment, page 95-125, In H. P. Singh, and others, eds. Handbook of sustainable weed management. Food Products Press, New York.
• Groff, S. Smart Cover Cropping [Online]
• Hoffman, M.L., and E.E. Regnier. 2006. Contributions to weed suppression from cover crops, page 51-75, In H.P. Singh, D.R. Batish, and R.K. Kohli, eds. Handbook of sustainable weed management. Food Products Press, New York.
• Manitoba Agriculture Food and Rural Initiatives (AFRI). Cover Crops on Special Crops Land (acc May 2010).
• Masiunas, J. 2006. Rye as a weed managment tool in vegetable cropping systems, page 127-158, In H.P. Singh, and others, eds. Handbook of sustainable weed management. Food Products Press, New York.
• New Brunswick Department of Agriculture and Aquaculture. 2008. Cover crops/Hay mulchin [Online]. (acc April 2010).
• Ontario Ministry of Agriculture and Rural Affairs (OMAFRA). Survey of Ontario Custom Farmwork Rates Charged in 2009: Provincial Summary.
• Snapp, S.S., and D.R. Mutch. 2003. Cover crop choices for Michigan vegetables. MSU Extension. Extension Bulletin E. 2896. October 2003. (PDF version)
• Verhallen, A., A. Hayes, and T. Taylor. 2003. Cover Crops: Hairy vetch [Online] (acc May 2010).
• Wallace, R.W., and R.R. Bellinder. 1992. Alternative tillage and herbicide options for successful weed control in vegetables. HortSci. 27:745-749.
• Wheeler B., and J. McKinlay. 2007. Forage Sorghum-Sudan Grass Factsheet [Online]. Available by OMAFRA.
• Wilson, D. 2005. Getting Started with Cover Crops: Selection and establishment tips for on-farm research [Online: rodaleinstitute.org/getting_started_with_cover_crops]

Acknowledgements

The main author, Bonnie Ball Coelho thanks Kristen Callow, OMAFRA (Ridgetown, Ontario), Robert Nurse, Agriculture and Agri-Food Canada (AAFC) (Harrow, Ontario), Diane Lyse Benoit, AAFC (Saint-Jean-sur-Richelieu, Quebec) and Danielle Bernier, Ministère de l'Agriculture, des Pêcheries et de l'Alimentation du Québec (Québec City, Quebec) for their collaboration, and recognizes research contributions from former AAFC specialists Robert Roy and Alex More. Photo credits: Bonnie Ball Coelho

This literature review and this factsheet were developed with funding provided by the Pesticide Risk Reduction Program of Agriculture and Agri-Food Canada's Pest Management Centre.

About the Pesticide Risk Reduction at Agriculture and Agri-Food Canada

The Pesticide Risk Reduction team delivers viable solutions for Canadian growers to reduce pesticide risks in the agricultural and agri-food industry. The team achieves this goal by funding integrated pest management projects and coordinating pesticide risk reduction strategies developed through consultation with stakeholders and pest management experts. Other sustainable crop protection factsheets are available. For more information please visit the Pest Management Centre.