What is weed management?

Answer 1

Organic weed management promotes weed suppression, rather than weed elimination, by enhancing crop competition and phytotoxic effects on weeds.[28] Organic farmers integrate cultural, biological, mechanical, physical and chemical tactics to manage weeds without synthetic herbicides.

Organic standards require rotation of annual crops,[29] 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.[28] Research is ongoing to develop organic methods to promote the growth of natural microorganisms that suppress the growth or germination of common weeds.[30]

Other cultural practices used to enhance crop competitiveness and reduce weed pressure include selection of competitive crop varieties, high-density planting, tight row spacing, and late planting into warm soil to encourage rapid crop germination.[28]

Mechanical and physical weed control practices used on organic farms can be broadly grouped as:[31]

• Tillage - Turning the soil between crops to incorporate crop residues and soil amendments; remove existing weed growth and prepare a seedbed for planting; turning soil soil after seeding to kill weeds;
• Mowing and cutting - Removing top growth of weeds;
• Flame weeding and thermal weeding - Using heat to kill weeds; and
• Mulching - Blocking weed emergence with organic materials, plastic films, or landscape fabric.[32]

Some critics, citing work published in 1997 by David Pimentel of Cornell University,[33] which described an epidemic of topsoil erosion worldwide, have raised concerned that tillage contribute to the erosion epidemic.[34] The FAO and other organizations have advocated a "no-till" approach to both conventional and organic farming, and point out in particular that crop rotation techniques used in organic farming are excellent no-till approaches.[34][35] A study published in 2005 by Pimentel and colleagues[36] confirmed that "Crop rotations and cover cropping (green manure) typical of organic agriculture reduce soil erosion, pest problems, and pesticide use." Some naturally sourced chemicals are allowed for herbicidal use. These include certain formulations of acetic acid (concentrated vinegar), corn gluten meal, and essential oils. A few selective bioherbicides based on fungal pathogens have also been developed. At this time, however, organic herbicides and bioherbicides play a minor role in the organic weed control toolbox.[31]

Weeds can be controlled by grazing. For example, geese have been used successfully to weed a range of organic crops including cotton, strawberries, tobacco, and corn,[37] reviving the practice of keeping cotton patch geese, common in the southern U.S. before the 1950s. Similarly, some rice farmers introduce ducks and fish to wet paddy fields to eat both weeds and insects.[38]