WEED MANAGEMENT IN CONSERVATION TILLAGE SYSTEMS FOR WHEAT PRODUCTION IN NORTH AND SOUTH-AMERICA

Soil erosion by wind or water is a serious problem in North and South America. When no-till or reduced tillage is used to control erosion, t he density of certain annual and perennial weeds can increase and new weed control techniques are usually required. The effects of conservat ion tillage on annual and perennial weeds, weeds that are spread by wi nd, plants from rangelands and pasture as weeds and volunteer plants a s weeds arc reviewed. Current weed control methods with minimum tillag e, herbicides, cover crops and other cultural practices in conservatio n tillage systems in North and South America are described. Some produ cers are successfully controlling weeds in continuous summer cropping systems in North America and in double cropping systems that include w heat in the winter and soybean or corn in the summer in Brazil, Argent ina and southeastern United States. Successful conservation tillage sy stems usually involve cropping sequences of three or more crop types a nd several herbicides. In these cropping sequences, the ground is cove red with a crop during most of the period in which the climate is favo urable for weed growth. Perennial weeds are a problem in all tillage s ystems and there is a general dependence on glyphosate for perennial w eed control. In successful conservation tillage systems, the amount an d cost of herbicides used is similar to that for herbicides used in co nventional tillage systems.