Mechanical weeding can be carried out on an entire field or it may be confined to selective inter-row weeding. Mechanical weeders range from basic hand tools to cutting-edge tractor driven devices. Mechanical weed control tools include cultivating implements such hoes, harrows, brush weeders and tines, and cutting or slashing tools such as string trimmers and mowers.
Determining Optimum Timings for Mechanical Weed Control
Establishing optimum timing for mechanical weed control and planting is determined by the competitive nature of the crop. For instance selecting optimal planting times for carrots can reduce weed and pest burden. Allium crops do not form a crop canopy to assist in competition against weeds and therefore may require constant weed control through to harvest. Once again timing is vital in mechanical techniques. Harrowing carried out before crop emergence kills off the first flush of small emerging weeds. This gives crops a competitive advantage over weeds. Research findings indicate that a spring-tine weeder was more effective in controlling corn poppy (Papaver rhoeas) in autumn while spring weeding was more effective chickweed (S. media). Tilling in autumn can eliminate winter annuals and biennials along with injuring perennials, while spring tilling can eliminate the initial growth of summer annuals.
Determining Optimum Technique for Mechanical Weed Control
Single inter-row weeding provides excellent weed control in a crop that quickly develops a broad and shading leaf canopy such as broccoli. As with any weed control method the rate of weed control required will depend on crop and weed characteristics so that slower growing crops such as sweet corn or those that have a long growing season such as green beans may need extra weeding depending on the competiveness of both weeds and crops.
Harrows
A harrow or a set of harrows is an implement used for breaking up and smoothing out the surface of the soil. Harrowing can be an effective mechanical method for dealing with annual weeds particularly before crop emergence in order to kill the first flush of small emerging weeds. This gives crops a competitive advantage over weeds. The best time to blind harrow is once there is a good weed cover using spring-tine, chain or drag harrows.
Spring-tine
A spring-tine (or spring tooth weeder harrow) is a type of harrow with many flexible iron teeth which is tractor mounted and designed to loosen the soil before planting and to disturb surface weed growth.
Chain or Drag Harrows
Chain harrows (also called drag harrows) have pull hooks on both ends which allow for heavy or light digging and can be flipped over for a smooth finish. Chain harrows can also be used on lake weeds.
Tractor hoes
Tractor hoes come in different shapes, designs and functions. All hoes are designed to cut through the soil at depths varying from 2 to 4cm. Findings show that while increasing cutting depth may not improve weed eradication a higher forward speed might help to reduce weed survival by increasing soil coverage of weeds. Tractor hoeing is best done under dry condition to avoid weeds regenerating and is highly effective in dealing with mature weeds.
Rotary hoes
Rotary hoes are designed for low or high residue fields and can be used either pre or post crop emergence. For this method crops need to be more deeply rooted than the weeds.
Hoe ridgers allow for inter-row and intra-row weed control. Hoe ridgers uproot weeds which are killed either through incorporation into the soil or by desiccation on the surface. For this reason it is important to decrease watering where possible after cultivation. Findings indicate that a soil covering of 1.5cm is adequate to kill small weeds and 2cm for larger weeds along with a relatively steep position of the hoe blade.
Timing
Tractor hoeing is highly effective in dry conditions as less re-rooting of the weeds is likely to occur.
Brush weeders
Brush weeders can be mounted to the front or rear of any tractor and are available as a complete unit or as an addition to other mowers and are ideal for narrow vineyards or wider spaces of orchards and fruit plantation.
Brush weeding (also known as Brush hoes) is a mechanical method of removing small weeds from row crops using rotating brushes of hard nylon bristles. Brush weeders come with a range of brush sizes as well as adjustable metal guards to safeguard young crops.
Brush weeding has been found to be very effective at the two to four true leaf weed stage. The success of this method relies on operator skill in tractor driving and guiding the brush weeder. Crop guards allow brushing as close as 20 mm either side of the crop rows. Another option is to install remote guidance systems on the weeder to replace the brush weeder operator.
Carrot are ideal crops to brush weed, with only one well timed brush weeding needed before canopy closure. Brush weeding operations are effective on both dry and moist soils; however weed seedlings can re-root if brushing is followed by rain.
Mowers Slashers and String Trimmers
String trimmers, also known as, edge-trimmers, strimmers, line-trimmers, whipper snippers or snipper whippers, weed whackers, or weed whips are powered handheld devices that use a flexible monofilament line instead of a blade for cutting weeds. It consists of a cutting head at the end of a long shaft with a handle or handles and sometimes a shoulder strap.
Mowers slashed/mowed material can be left to form natural mulch.