Population Variability in the Response of Ripgut Brome (Bromus diandrus) to Sulfosulfuron and Glyphosate Herbicides

Abstract

Ripgut brome has become a problematic weed in Spain both as a consequence of the continuous cropping of winter wheat through minimal tillage systems and its difficult control with selective herbicides. Ripgut brome populations collected in the regions of Castilla-León and Cataluña, two main cereal-growing areas in Spain, were screened in the greenhouse for response to sulfosulfuron, a selective herbicide for the control of brome grasses in wheat, and to glyphosate, often used as a pre-plant knockdown to control bromes in no-till systems. The fresh weight percentage relative to the untreated controls was calculated for each ripgut brome population and herbicide and was used as a measure of the herbicide response. Results showed variation in fresh weight response to both herbicides among populations. Fresh weight of the populations after sulfosulfuron was applied at the two-leaf stage at a rate of 20 g ai ha−1varied from 3% in the most susceptible population to 35% in the most resistant; the response was similar (6 to 38%) when the herbicide dose was reduced to half. For glyphosate at 800 g ae ha−1, fresh weight varied from 2 to 25% among populations, but the range of variation in fresh weight response increased as herbicide dose decreased to one half, with rates of from 4% to 90% among populations. The location of the collection site (inside the field or in-margin) showed no differences in response to both herbicides, but there was a statistically significant, geographically correlated differentiation for glyphosate response, with a greater resistance in the populations from Castilla-León. Undamaged plants were found after treatments with both herbicides, showing differences in resistance among plants. The study shows inter- and intrapopulation variability for the response of ripgut brome to sulfosulfuron and glyphosate. The implications for resistance development are discussed within the framework of relationships of the structure of the populations relative to their herbicide response.