Effects of Quinclorac on Following Rotational Crops

Quinclorac was registered for weed control in wheat ( Triticum spp.) for western Canada in 1997. Residues from quinclorac may persist in the soil and may damage following crops; therefore, field and growth chamber experiments were conducted to determine the tolerance of several following rotational crops. Cereals and bromegrass ( Bromus biebersteinii ) were sufficiently tolerant that they could be seeded within 16 d of quinclorac application without risk of injury. At the other extreme, marketable and total potato ( Solanum tuberosum ) yields were reduced by quinclorac on irrigated land 1 yr after application. Growth chamber experiments were used to rank crops in order of their tolerance of quinclorac residues and to compare the tolerance of crops that were grown in the field with additional crops. Quinclorac injured several legume and oilseed crops when the crops were seeded immediately after application, but quinclorac did not reduce the dry matter yield of two of the most sensitive legumes, faba bean ( Vicia faba ) and alfalfa ( Medicago sativa ), 1 yr after application on irrigated land. However, based on a previous study, one can conclude that injury to these crops may occur in the field under drought conditions in rain-fed agricultural systems.