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  A Publication of UVM Extension's Vermont Vegetable and Berry Program

Ten Steps Toward Organic Weed Control

by Vern Grubinger
Vegetable and Berry Specialist
University of Vermont Extension

About one third of  Vermont's vegetable farms are managed organically. On many others, herbicides are used only on a few of the crops. Vegetable farms here and throughout New England are relatively small, and tend to have many plantings of highly diverse crops, making it a hassle to spray different materials at different times. Necessity being the mother of invention, growers are finding ways to keep ahead of weeds using only cultural and mechanical methods. While some battles are lost, some growers are winning the war and their fields are kept remarkably clean without herbicides.

Many of the tactics below are commonly used by the organic growers in New England, and may have application to other regions and larger scale of production. Here are 10 steps toward successful non chemical weed control:

1) LOWER WEED PRESSURE by managing your weed seed bank to reduce the need for cultivation and hand hoeing.

  •  Thoroughly compost animal manures to kill off weed seeds, or avoid using manure altogether.
  •  Keep weeds from going to seed: cultivate solely for that purpose, or handful, if necessary.
  •  Reduce weed influx by keeping alleys and field edges mowed or harrowed.
  •  Power wash tillage equipment after use in fields with a noxious weed problem.
2) DIVERSIFY ROTATIONS to keep a particular weed from proliferating.
  •  Try to alternate crops with different tillage requirements or time of planting.
  •  Include small grains or sod crops in the rotation if possible, to vary the habitat for weeds.
3) USE COVER CROPS because they compete with weeds while providing other benefits.
  • Select species for rapid growth that can starve weeds of light and nutrients. In the northeast, overwintering hairy vetch plus rye or hairy vetch plus oats mixtures are popular as a spring cover crop. Buckwheat, sorghum-Sudangrass, or Japanese millet work well in the heat of summer. Ryegrasses, oats or other small grains provide fall cover and winter erosion control.
  • Sow at high rates, drill the seed and even irrigate if necessary to assure thick stands and rapid establishment of cover crops.
  • Regular incorporation of cover crops (green manuring) enhances soil tilth, making cultivation easier. Since frequent cultivation can harm soil structure, it is important to compensate by adding clean organic residues whenever practical.
4) FEED THE CROP, NOT THE WEEDS by manipulating fertilizer placement and timing.
  • Avoid pre-plant broadcasting of soluble nutrients that may be more readily utilized by fast-growing weeds than slow-growing crops, and may even stimulate weed germination.
  • Apply fertilizer near the rows where it is more likely to be captured by the crop.
  • When using expensive bagged organic fertilizers, band at low rates at planting or sidedress; rely on mid-season release of nutrients from compost and/or green manures for primary fertility.
5) PICK THE RIGHT TOOL FOR THE JOB. Cultivation is critical to weed control on organic farms, and doing it right requires a variety of tools that can be matched to the weed, crop and soil situation. Over the season, different tools are needed as the crops and/or weeds get larger.
  • Blind, "over-the top" cultivation controls very small weeds, just germinated or emerged, before and sometimes after planting. The entire surface of the field is worked very shallow using flex-tine cultivators (e.g. Lely weeder), or rotary hoes.
  • Shallow between-row cultivators such as basket-weeders, beet-hoes, or small sharp sweeps are used to cut off and uproot small weeds after the crop is up. These can get very close to the crop when it's small, without moving much soil into the row, and may be the only tools used on delicate crops like leafy greens.
  • As vigorous crops grow, soil can be thrown into the row to bury in-row weeds using rolling cultivators (e.g. Lilliston), spyder wheels (e.g. Bezzerides), large sweeps or hilling disks. Some of these tools can be angled to pull soil away from the row when plants are small, and later turned around to throw soil back on the row during subsequent cultivations.
6) COMBINE TOOLS to cover the different zones in the field.
  • Between-row, in-row, and wheel-track weeds must all be attacked.
  • Watch out for narrow strips that are missed because they pass between too-few tools.
  • Front-mounted or belly-mounted tools plus rear-mounted toolbars facilitate combinations that can assure complete coverage.
7) SET UP FOR SPEED to minimize cultivation time and expense.
  • Perfectly straight rows and alert tractor drivers are essential
  • Uniform row spacing across comparable crops enhances the utility of a cultivation set-up.
  • Consider multiple-row units; gauge wheels are helpful on wide units or if fields aren't level.
  • With frequently-used tractor-mounted cultivators, get them set just right and leave them on all season to avoid repeated mounting and adjustment.
8) TIMING IS EVERYTHING: get the weeds while they're small, before the field looks weedy.
  • Very shallow cultivation of "white thread" weeds can minimize bringing up more weed seeds.
  • Keep an eye on the weather and try not to get beat by the rain; if you do, be ready with the heavy artillery - more aggressive tools for bigger weeds, when you can get in.
  • Prepare soil for planting, then use a flamer to kill very small weeds without disturbing the soil.
  • One or two flamings are used, just before and/or after planting, but prior to crop emergence.
  • Single burners flame just the crop row, multiple burner units cover a whole bed.
  • Backpack, push-type and tractor-mount units are in use.
10) EXPERIMENT to fine-tune your weed management tactics.
  • Start on a small scale with tools and techniques that are new to your farm.
  • Identify your problem weeds and compare different combinations of rotations, cover crops, and cultivation tools for their effectiveness in providing control.
  • Keep an eye our for new tools, or new ways to use old tools.
  • Leave a "control" row or section untreated, so you can see the effectiveness of your tactics.
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