Herbicide-resistant crops as weeds in North America.

Abstract

Abstract Growers have rapidly adopted transgenic herbicide-resistant (HR) crops, such as canola ( Brassica napus L.), soyabean [ Glycine max (L.) Merr.], maize ( Zea mays L.) and cotton ( Gossypium hirsutum L.), across North America (USA and Canada) since their commercial introduction in the 1990s. With their widespread cultivation, increasing attention is focused on management of HR volunteers in crops that follow in rotation. In this review, we describe the impact and management of HR crop volunteers in different agroecosystems in North America. The relative risks of planting HR crops and subsequent potential for volunteerism of these crops are assessed. HR volunteers are common weeds and the relative weediness depends on species, genotype, seed shatter prior to harvest and disbursement of seed at harvest, management practices, and environment. Chemical control options may be more limited if the crop volunteers are HR. There are generally no marked changes in volunteer weed problems associated with these crops, except in no-tillage systems when glyphosate (GLY) is used alone to control volunteers. The increasing use of GLY in North American cropping systems, spurred by increasing area and frequency in rotation of GLY - HR crops, may require increased alternative herbicide use or other novel tactics to control GLY-HR crop volunteers.