Biological activity, availability and duration of phytotoxicity for imazamox in four different soils of central Italy

Greenhouse bioassays were carried out from 1999 to 2002 on several types of soils of central Italy to assess the carry‐over risk of imazamox residues to non‐target crops. No observable effect levels (NOELs) were determined on quartz sand; sugar beet showed the highest sensitivity to imazamox (NOEL 0.4–0.8 ng a.i. mL^?1 of substrate), followed by spinach, oilseed rape, fennel, cauliflower and lettuce (NOELs from 1 to 5 ng a.i. mL^?1 of substrate). Wheat, sunflower, grain sorghum and maize were not very sensitive to this herbicide. Imazamox availability was greatest on sandy soils and decreased in soils with high clay or organic carbon content, where herbicide efficiency was less than 50%, with respect to non‐sorptive media. The decline of herbicide efficiency was quick in sandy soils, where herbicide efficiency dropped to 50% in less than 3 days. In clay‐loam or organic soils, 50% relative efficiency was reached in 15–33 days. Such results suggest that imazamox sprayed at normal field application rates can pose slight risks of carry‐over of residues, which may damage very sensitive species (sugar beet, oilseed rape and spinach) in sandy soils. In these cases, safe recropping intervals of 1–3 months are required, so current label guidelines for imazamox are adequate to protect rotational vegetable crops in central Italy.     

Effect of adjuvants on the rainfastness and performance of tribenuron‐methyl on broad‐leaved weeds

The influence of a non‐ionic surfactant (20% isodecyl alcohol ethoxylate plus 0.7% silicone surfactants), an anionic surfactant (25.5% alkylethersulfate sodium salt), and a vegetable oil (95% natural rapeseed oil with 5% compound emulsifiers) on the performance and rainfastness of a new commercial formulation of tribenuron‐methyl was assessed on four broad‐leaved weeds: wild mustard (Sinapis arvensis), scentless mayweed (Tripleurospermum inodorum), common poppy (Papaver rhoeas), and common lambsquarters (Chenopodium album). In one experiment, six doses of tribenuron‐methyl alone or in a mixture with each of the three adjuvants were applied to each weed species at two different leaf stages. In another experiment, the plants of T. inodorum were sprayed and subsequently subjected to 3 mm of rain at 1, 2, and 4 h after treatment (HAT). The activity of tribenuron‐methyl was significantly enhanced by all the adjuvants on all the weed species and only minor differences were observed among the tested adjuvants. The impact of the adjuvants varied among the weed species and growth stages. The highest response to the inclusion of adjuvants in the spray liquid was found at the late growth stage and on C. album, followed by P. rhoeas and T. inodorum, while S. arvensis was less responsive to the adjuvants. All the adjuvants significantly improved the rainfastness of tribenuron‐methyl on T. inodorum, with differences among the adjuvants being more pronounced when rain occurred shortly after herbicide application. The effect of the vegetable oil on tribenuron‐methyl's rainfastness was significantly lower than that of the surfactants with rain at 1 HAT, while no significant differences among the three adjuvants were observed when rain occurred at 2 and 4 HAT.