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, but shallow tillage between short cycles of cover crop growth is effective.  The tillage kills weed seedlings and encourages germination of a new “flush” of weeds that can be killed with the next disturbance.  Through these cycles, the objective is to encourage weed seed germination but not to allow further weed seed production.  A dense stand will provide weed suppression while it is growing which is important for a season-long cover crop in which weeds may mature and set seed.  Cover crops 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 increase in long-term sod crops, e.g., one or more years of red clover.  

Fallowing is not planting a field with the intention to reduce weed seed populations. Repeated shallow soil disturbance will encourage weeds to germinate while subsequent events kill seedlings before they go to seed. Even in the absence of a cover crop, this strategy will reduce the weed seed bank of a field.
Plant competition is the foundation of weed management.  Remember, “the big get bigger.” Large-seeded crops and transplants have an initial size advantage over weeds.  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. Choose high quality seed, calibrate equipment to ensure accurate seeding rates and depth, and where possible, supply resources selectively to the crop, e.g., apply fertilizers banded below/near the crop row, or drip irrigation, instead of broadcasting.

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 allowing 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. However, as noted above, a well-prepared seedbed will help weeding tools function to their potential during later cultivation events.

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.