Alternative weed control options

Alternative weed control options should always be considered as part of the weed control program, before resorting to herbicides.

Control Method - Cultural techniques

• Hygiene: avoid transfer of weed propagules (clean equipment etc), quarantine, avoid seed set, prevent establishment, decrease weed seed reservoir
• Ecosystem manipulation: uses changes in soil fertility (nutrition, pH), drainage, irrigation (eg use drippers to restrict water), planting density and depth, planting date etc to control weeds
• Physical barriers: mulching-synthetic and natural
• Materials brought in from other sites are quarantined

Control Method - Mechanical control

• Hand pulling: slow but very selective and can prevent damage to vulnerable plants nearby
• Slashing or mowing: may not be suitable for some weeds eg creeping oxalis (Oxalis corniculata)
• Brushcutting: expensive, but can give good control, especially suited to linear features such as fences
• Cultivation: may cause soil erosion or create seed bed for new weeds to establish

Control Method - Thermal weeding

Burning will break dormancy of many weeds: which can then be destroyed (eg Apple of Sodom Solanum hermanni or Gorse Ulex europaeus). 55% minimum (80% - 100% for persistent weeds or thick seed coat)

Can stimulate germination of some weeds leading to new problems - may be dangerous and need to be restricted to certain times of the year to avoid wildfire hazard

Solarisation: cover soil with clear polyethylene sheet (40 -100 % thick) and seal:

• secure the edges of plastic sheet
• soil must be moist
• can kill weed seeds and diseases
• allow a minimum four weeks treatment, depending on daytime temperatures

Control Method - Use of vegetative cover

The best way to exclude weeds is to use dense plantings of hardy competitive species which will suppress weed growth. Once established, they should require little maintenance. Closely planted trees may achieve this effect once the canopy closes over, but the technique is more often used for groundcovers.

Use of vegetative cover is the most desirable form of weed control, from an ecological perspective. This strategy includes the use of "living mulch" grown to out-compete weeds. Vegetative cover has the following advantages:

• prevents new weeds from germinating or smothers weed seedlings.
• keeps the soil covered and protected from wind and water erosion.
• protects the soil ecology, by insulation, temperature control and continuous addition of small quantities of organic matter.
• keeps the soil active - plant roots are continually exploring the soil profile and stimulating soil biology as they grow.
• provides food sources or habitat for small animals, birds, insects and other organisms.
• appropriate species are selected and well grown they will require little maintenance and will compete very little with crop plants.

Factors which influence the economics of this choice include the following

• location and seasonal variation which will influence the number of times per year that grass swards need to be mown or groundcovers replaced.
• aesthetic requirements of the site.
• slopes, such as steep batters, where machinery access is difficult.
• the ratio of edge to planting area (ie the length of boundary that needs to be maintained against weed infestation).
• weed resistance of the species chosen for living mulch or groundcover.
• weed species present (eg rhizomatous or stoloniferous perennial weeds such as couch or kikuyu may be very difficult to remove from groundcover or massed shrubs).
• growth rate of species used.
• requirement of species used for additional inputs (fertiliser, irrigation etc).
• quality of planting stock.
• longevity of living mulches or groundcovers.

Generally, the groundcover species used should be selected to be self replacing, or to have a long life expectancy, but should not themselves become weedy, for the technique to be competitive.

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