Greenhouse studies were conducted to determine the responses of ripgut brome and foxtail brome to MON 37500 applied at rates up to 80 g/ha. At 30 d after treatment MON 37500 at 20 g/ha reduced fresh weight of ripgut brome by 89% when applied at the three-leaf stage and 57% when applied at the tillering stage. MON 37500 at 10 g/ha reduced fresh weight of foxtail brome by 80% when applied at the three-leaf stage and 61% when applied at the tillering stage. Rates above 20 g/ha did not increase control of either species. In field experiments during 1998 to 1999 and 1999 to 2000 in Settat, Morocco, bread wheat tolerated MON 37500 at 67 g/ha. Ripgut brome control in the field was 78% in the first growing season and 90% in the second season when MON 37500 was applied at 27 g/ha to brome plants at the one- to four-leaf stage. A similar rate controlled tillering ripgut brome by 69% during 1998 to 1999 and 62% during 1999 to 2000. MON 37500 at 20 to 30 and 10 to 20 g/ha applied before tillering controlled ripgut brome and foxtail brome, respectively, ≥ 70%.

The objectives of this study were to determine the efficacy and risk of controlling weeds at reduced herbicide rates under various environmental and biotic conditions, through analysis of published data on the use of below-labeled rates of herbicides. A database was established by extracting information from previously published papers on weed control at below-labeled rates of herbicides in crop production systems over large geographical and temporal scales. The database was then analyzed to evaluate the efficacy and risk of using herbicides at various reduced rates under different management systems. Using below-labeled herbicide rates in conjunction with interrow cultivation is an effective way of reducing herbicide input in agricultural systems while maintaining satisfactory weed control. There are greater opportunities for herbicide reduction using preemergence (PRE) than preplant incorporated (PPI) or postemergence (POST) herbicides, in coarse-textured than in fine-textured soils, and in corn than in soybean or wheat. The success of reducing herbicide rates does not depend on whether the herbicides are applied in conventional or conservation tillage systems or whether they are used with or without adjuvants. The above conclusions are based on studies conducted in experimental fields where weed pressures may be subjectively chosen to be high. Greater potential for herbicide reduction may exist at locations or in cropping systems were weed pressure is low.