Cultural Weed Management

Cultural options include cover crops, fallowing, plant competition, mulches, soil preparation, stale beds, and crop rotation.

Cover Crops alone do little to reduce overall weed populations.  A dense stand will provide weeds suppression while it is growing.  They can also slow the warm-up of soil and provide shade, both helping to slow weed seed germination and reduce the soil seed bank over time. Perennial weeds will be largely unaffected.  Soil disturbances between short cycles of cover crop growth are effective.  The tillage kills germinated weeds and also moves weed seeds up to near the soil surface where they can germinate prior to the next disturbance.  Through these cycles, the objective is to encourage weed seed germination but not to allow further weed seed production.

Fallowing is not planting a field with the intention to reduce weed seed populations.  For annual and biennial weeds, physical weed control is best.  Repeated soil disturbances (disking, rototilling) before weeds go to seed, even in the absence of a cover crop, will reduce the weed seed bank of a field.

Plant competition can reduce weed pressure.  Use of transplants, rather than direct seeding where possible, will allow the crop to get a jump on the weeds and provide shading of the soil which will delay weed emergence and competition.  Decreasing the space between crops will also increase soil shading.  Overall, the more rapidly a crop can cover the soil ahead of weed emergence, the more competitive that crop will be.

Mulches are often used to control weeds.  Mulches can be organic (straw, hay, grass clippings, dead cover crops) or inorganic (plastic).  Organic mulches are effective if they are thick enough to keep weeds from emerging through them (usually at least 2-3").  Downsides of organic mulches are that they can be expensive, they slow soil warm up or reduce soil temperatures, and they can harbor animal pests.  Cooler soil temperatures can be a problem in warm season crops.  It is recommended that the mulch application be delayed to allow the soil to warm up sufficiently for the crop.  Black plastic mulches will warm soil and eliminate weed pressure.  However, weeds emerging through the planting holes and between strips of plastic mulch can still reduce yields if not controlled.  Infra-Red Transmitting (IRT) mulches are less effective than black plastic for controlling weeds, and clear mulches can enhance weed growth.  Some growers plant cover crops between plastic mulch strips as "living mulch", but these cover crops can also compete with the crop.  Killing the living mulch before the crop is planted, mowing the mulch on a regular basis, or using raised beds will help to reduce but not eliminate competition.  See the section on using herbicides in combination with plastic mulches later in this section.

Proper soil preparation can influence weed emergence.  Soils which are rough and less firmly packed will yield fewer weeds than those that are more finely worked, more compacted, and more uniformly moist.

Stale seedbed or summer fallowing is performed on fields that have been prepared for planting, either in the spring before a crop is sown, or in the summer after a spring crop but before a fall crop. The soil is then lightly disturbed on a regular basis to kill small weeds as they emerge, without bringing up new weed seeds from below the top few inches of soil. Early in the year, broadleaves will not be controlled if they have not yet emerged, so a summer fallow works better on them. Perennial weeds may be weakened but not killed. Tools that can be used for this practice include chain-drag, spring-tooth harrow, light-weight disc harrows, or tine weeders.  See additional information on the stale seedbed technique later in this section.

Crop rotation can be a tool for managing weeds. Weed species present tend to be most like crop planted. Examples include grasses in corn, winter annuals with early-planted crops, and perennial weeds with perennial crops. Rotating crops among these groups will tend to disrupt this trend.