ALL THINGS ORGANIC - Control weeds organically

by Ian Cushon
June 11,1998

One question I hear often as an organic farmer is how do you control weeds?

Weed management on organic farms requires patience and tolerance. Every growing season is different and I learn something new each year. Some strategies work well one year, but the next they don't. But there are some principles to organic weed management that can also be used to reduce herbicide use on conventional farms.

Understanding weeds and their growing habits is important. One of the best resources I have seen is published by Alberta Agriculture, Guide to Crop Protection in Alberta - Part 2 Non- Chemical Control. To order, phone 1-800-292-5697. This guide also covers disease and insects and gives good recommendations on cultural and mechanical control methods. Experienced organic farmers also are an important source of information.

Providing a competitive crop goes a long way to controlling weeds. Good field preparation is important. Fall and early spring tillage sets back perennials and encourages annual weeds to germinate. Providing a firm, fertile and moist seedbed is crucial to establishing a healthy competitive crop. Using high quality seed and selecting varieties of crops for their weed-competitive characteristics are musts. Seeding heavier than normal to provide more plants per square foot to crowd out the weeds is also recommended for most crops. These are the first lines of defence for organic weed management. Fortunately we have a good selection of competitive crops such as wheat, oats, rye and barley. Cereal crops generally compete well if they have good fertility. Weeds compete better in low fertility soils, so providing the good soil fertility is important.

I also use pre- and post-emergent tillage. Some deeper-seeded crops such as sunflowers emerge slowly. Before they emerge and after weeds have come up, you can kill weeds by harrowing or rodweeding. Sunflowers and wheat are easily harrowed after emergence. Some organic farmers even post-emergent harrow and rotary-hoe more sensitive crops. But exercise caution. Thinning a stand with harrowing to control a few weeds may not be a benefit. It is best to experiment on a small scale until you feel confident. I grow sunflowers in 30-inch rows. This allows me to cultivate between the rows for effective weed control. A few organic farmers are row-cropping lentils and flax in narrower rows, again to allow inter-row cultivation.

Weed management is more difficult in non-competitive special crops such as lentils, peas and flax. Don't seed these crops on summerfallow. Summerfallow is often cleaner than stubble, but it is also more fertile, which encourages weed growth. Summerfallow usually produces a flush of healthy weeds. So you need a competitive crop like wheat, which also can use the fertility to produce good protein. I sow peas, Laird lentils and flax on wheat stubble later in the seeding season after some weeds have grown. The legumes will fix their own nitrogen on stubble and do well, while the weeds, such as green foxtail, will struggle with nitrogen deficiency and be stunted. Lentils and peas are more adapted to stubble cropping and you can plant a third crop of barley or oats on the pea and lentil stubble. If you under seed the third crop to sweet clover, then essentially you have a continuous cropping rotation.

Ian Cushon
Moose Creek Organic Farm Inc.
P.O. Box 85
Oxbow, Saskatchewan
Canada, S0C 2B0

Tel. 306-483-5034
FAX 306-483-2799
Cell 306-483-8257
E-mail: coldridge@sasktel.net