Applying organic principles to weed control

An important principle of organic growing is to work with nature where ever possible and to imitate nature in the design of the production system. The extent to which this is possible may vary greatly between individual enterprises depending upon location, crop, scale, stage of development and other site-specific factors. Organic growers generally work actively to create this complexity.

Preservation or re-creation of “natural” ecosystem areas is often an important aspect of this on organic farms, because indigenous native vegetation is generally able to support a resource of biological controls with little cost or management required over a long term (establishment many be expensive initially). Organic growing has many potential benefits for the wider community, especially in providing an example of excellent environmental management and sustainability practices. Organic farms such as BD Paris Creek (SA) and Garry Hannigan (NSW) are acknowledged for environmental excellence and feature prominently in environmental awards.

Organic growers are often distinguished from non-organic growers by the extent to which they can include increased biological diversity within the actual production area itself. A garden scale example would include use of companion plants for pest control, a market gardening example might be ‘under-cropping’ or ‘cover-cropping’ with prostrate legumes, cereal producers in favourable areas may under-sow with medics, and an example of orchard and tropical application of this idea was provided by the cover story of the last issue of acres. Andre and Julia Leu have developed an excellent system of cover-copping with Singapore daisy and various tropical legumes.

Organic producers are much less concerned with the presence of weeds as such, than the ecological role or function of the particular weed species and the ease with which they may be controlled. The best weeds are species that are themselves easy to control, but will compete effectively with the harder to control species. A fine example of this is use of oxalis (sour sob) down the orchard or vineyard row, under the drip line. This system is used by many organic grape producers or orchardists, such as Graham and Annemarie Brookman, from The Food Forest at Gawler (SA). The Food Forest is an excellent example of an organic permaculture property incorporating many features into an integrated, productive property. Organic viticulturists such as Adrian Strachan, from Willunga, find that oxalis out competes many other weeds, but dies down early in the season. It is no longer actively growing when the vines are in strong growth, and their need for moisture is greatest, and when other weeds, such as grasses, would be competing for soil water.

Developing a system such as this requires some careful planning and experimentation, to ensure that the system can be managed. Weeds may compete with crop plants for water, nutrients and sunlight, and they may harbour pests and diseases. For instance, thistles may harbour Lettuce Yellows Necrotic Virus (LYNV). Weeds may also provide some positive services such as providing nutrients (legumes), cycling and sequestering of nutrients, adding organic matter. They may also provide habitat for predators of pests and beneficial organisms that compete against or attack pathogens. Weeds may also prevent soil erosion, by reducing the rate of flow of runoff and by binding soil with roots, or they may help to preserve soil structure, for example by improving recovery of soil from compaction after harvest, in a vineyard or orchard, and improving trafficability after rain (reduced rutting etc)).

Goals of organic weed management

The goals of organic weed management may vary from the goals of non-organic producers. Organic growers are more inclined to accept, and even encourage, a population of non-crop or weedy species, in order to increase the biological complexity of the farm or garden.