General Overview of Weeds in Crop Systems
Weeds often reduce crop quality quite dramatically. For example, grasses are often green when cotton (Gossypium spp.) is harvested with a mechanical cotton picker. Grass is drawn through the spindles resulting in stained cotton fibers, thus greatly reducing the value of the cotton. Contamination of grain with weed seed or weed chaff diminishes grain value. Wheat that is contaminated with aerial bulblets of wild garlic (Allium spp.) is virtually unmarketable for milling. Where pigweeds (Amaranthus spp.) are uncontrolled in mint (Mentha spp.), crop quality suffers greatly; only small proportions of pigweed biomass in the harvested mint renders mint oil unmarketable (Table 9).