Weed management

• Organic weed management promotes weed suppression, rather than weed elimination, by enhancing crop competition and phytotoxic effects on weeds.
• Organic farmers integrate cultural,biological, mechanical, physical and chemical tactics to manage weeds without synthetic herbicides.
• Organic standards require rotation of annual crops, meaning that a single crop cannot be grown in the same location without a different, intervening crop.
• Organic crop rotations frequently include weed-suppressive cover crops and crops with dissimilar life cycles to discourage weeds associated with a particular crop.
• Organic farmers strive to increase soil organic matter content, which can support microorganisms that destroy common weed seeds.

Mechanical and physical weed control practices used on organic farms can be broadly grouped as:

a) Tillage – Turning the soil between crops to incorporate crop residues and soil amendments; remove existing weed growth and prepare a seedbed for planting;

b) Cultivation – Disturbing the soil after seeding;

c) Mowing and cutting – Removing top growth of weeds;

d) Flame weeding and thermal weeding – Using heat to kill weeds; and

e) Mulching – Blocking weed emergence with organic materials, plastic films, or landscape fabric

• Naturally derived insecticides allowed for use on organic farms use include Bacillus thuringiensis (a bacterial toxin), pyrethrum (a chrysanthemum extract), spinosad (a bacterial metabolite), neem (a tree extract) and rotenone (a legume root extract).

• These are sometimes called green pesticides because they are more environmentally friendly than synthetic pesticides.
• Naturally derived fungicides allowed for use on organic farms include the bacteria Bacillus subtilis and Bacillus pumilus; and the fungus Trichoderma harzianum. These are mainly effective for diseases affecting roots.
• Some naturally derived pesticides are not allowed for use on organic farms. These include nicotine sulfate, arsenic, and strychnine.
• Synthetic pesticides allowed for use on organic farms include insecticidal soaps and horticultural oils for insect management; and Bordeaux mixture, copper hydroxide and sodium bicarbonate for managing fungi.