Mechanical Control of Weeds

In many situations, herbicides cannot be used or are not effective in controlling all the weeds. In these situations, cultivation and hand pulling are often the only available options. Either should be done on young weeds, before they compete with bedding plants and before they set seed.

Cultivation works well on small annual weeds; perennials will often regrow from the roots even if the top is removed. Also, remember cultivation can stimulate successive flushes of germinating weeds by bringing new weed seeds near the soil surface. You will need to check for emerging weeds on a 2- to 3-week cycle if you are routinely cultivating.

Hand pulling is also an essential part of any weed management program. No weed management program will control all weeds. Weeds which escape the management program need to be removed before they produce seeds.

A landscape mulch is a layer of either inorganic or organic material placed on the soil surface. When the mulch layer is sufficiently deep, weed emergence is greatly reduced but not entirely eliminated.

The combination of a mulch and hand pulling of small weeds before they flower and produce seed can be a very effective weed control strategy.

In addition to weed control, other potential benefits of a mulch include: improved appearance of the landscape, water conservation through reduced evaporation from the soil surface, reduced soil erosion by wind and water, and reduced crusting of the soil surface.

For organic mulches, potential benefits also include increased water absorption, percolation and aeration as the soil structure is improved over time by the addition of organic matter.

Perennial weeds require repeated removal of above-ground portions of the plant to exhaust the underground food reserves. Following hoeing or close mowing, perennial plants use stored food reserves to regenerate shoots and foliage.

When these shoots reach sufficient size, they replenish the underground food reserves. Thus, to eradicate perennial weeds mechanically, the foliage must be destroyed every two to four weeks for one or two years. If the foliage is allowed to regrow, then perennial weeds recover and eradication is delayed.

After five or six timely hoeings, perennial weed density will decline but mechanical control must be continued until the infestations are eradicated. Perennial weeds are more difficult to control due to their ability to generate new growth from rhizomes, stolons or tubers and the large size of the underground root structures makes it very difficult or impossible to eradicate them by digging up the underground portions of the plants.

If preemergence herbicides have been applied and activated, they should be left undisturbed to be effective. Cultivation disrupts the herbicide barrier and lessens the effectiveness of the herbicide. Therefore, cultivation should be shallow and used sparingly if a preemergence herbicide has been applied.