Weed control is real challenge for vegetable growers. For many reasons, there is increasing interest in non-chemical controls. At the same time, many growers are working harder to improve their soil quality. Some non-chemical weed controls are good for the soil; some are not. Below I consider six non-chemical weed control practices, ranked roughly from best to worst in terms of soil impact.

1. Mulching with organic materials. Growers commonly do this for berry crops; why not more for the vegetables? One example I know of that works very well is to put down clean straw or hay in the aisles between black plastic for crops such as tomatoes or peppers. When coupled with trellising of tomatoes, this practice also helps with disease control. Mulch also works well with summer squash and some brassica crops.

Galinsoga and many other annual weeds will be well-controlled by a good mulch. Perennial weeds will not, and will thrive under mulch. For them, try cover crops and fallow treatments.

2. Crop rotation. Preferably including a legume/grass sod crop, but at least with crops that are tilled in different seasons. Weeds will build up more if they are consistently favored by tillage at their favorite time. Warm season weeds such as pigweed, purslane, and crabgrass are favored by tillage in June and July--and will be smothered out by mulch or cover crops at that time. Galinsoga seeds have only a short life in the soil. A field rotated into three years of hay would have a dramatic reduction in galinsoga pressure, plus an improvement in soil tilth.

Many midwestern studies have shown yield increases of 10% or more in corn and soybeans in their first year of rotation, compared to continuous cropping. This is called the rotation effect. No doubt it works for most vegetables as well--take advantage of it.

2a. Rotation and herbicides. Use crops in rotation to get rid of pesky weeds via wider herbicide options. This should be a cornerstone of weed IPM. For instance, growing sweet corn allows one to use Dual, which can help clean up a field with heavy annual grasses, galinsoga, nightshade or nutsedge. If you cultivate the corn as well, so much the better for your weed control. If horse nettles are a problem in a field, plant an early-maturing crop such as peas, snap beans, cucumbers, summer squash, etc. Then either till repeatedly after the crop is harvested (ie, fallowing the field) or spray with Roundup and Banvel or 2,4-D . Velvetleaf is quite susceptible to cultivation, so rotating into a crop that you can cultivate thoroughly can help. Field crops may present more herbicide options. As much as possible, plan so that herbicide carryover does not preclude your rotation choices.

3. Cover crops. Use them in rotation, as above. Fill in "windows" before or after a crop, of 5 weeks or more during the growing season, with a cover crop that will grow rankly in that season. Plant it thickly. For instance:

Warm season--sudangrass, Japanese millet, cowpeas, soybeans, buckwheat
Cool season--oats, rape, field peas
For overwintering--rye, hairy vetch, red clover

If the window is less than 5 weeks, consider fallowing during that period by harrowing the field every 10 days. Don't let weeds escape and set seed!

As the cover crops grow, they smother weeds that germinate. And when you till the cover crop under, the weeds are also destroyed before they go to seed. Even if the cover crop has not reached its full growth, till the stand under if you see weeds beginning to flower.

4. Cultivation. Learn about the best tools for your crops and soils, and how to use them. Talk to other growers who cultivate. Two excellent resources are the video, "Vegetable Farmers and Their Weed Control Machines", and the book, Steel in the Field. Both are available on loan from my office. Cultivation, if done well and in conjunction with other methods listed here, can achieve good weed control at a competitive cost.

5. Stale seedbed. This is a technique used to clean up a field before planting the crop. Prepare your seedbed, but delay planting until a flush of weeds emerges. Then shallowly harrow them, or flame them, or spray with a low rate of Roundup before seeding the crop. You will be depleting the weed seed pool in the top inch of soil. This process may be repeated several times, if your planting schedule permits. Stale seedbed does not work well against perennial weeds, unless herbicides or repeated flaming are used.

6. Fallow. This involves repeated discing or harrowing of the field during a substantial mid-summer time period (often 6-8 weeks) to kill weeds. It can be done after some very early crops such as spinach or lettuce, or incorporated into a "year off" with cover crops. Fallowing is an effective way of cleaning up fields infested with most weeds. It is a last resort for most growers, because of having to take the field out of production, and because it is relatively hard on the soil.