Published online by Cambridge University Press: 12 June 2017
Drift of sulfonylurea and phenoxy herbicides from spring cereal fields to nearby spring pea and lentil crops was simulated by spraying pea and lentil with 2,4-D or the 2:1 commercial mixture of thifensulfuron and tribenuron at rates of 0, 0.33, 1, 3.3, or 10% of the use rates (X) for spring cereal crops approximately 3 and 5 wk after planting pea and lentil. 2,4-D had minimal inhibitory effects on both crops at all rates tested. Lentil was slightly more sensitive than pea to 10% X 2,4-D. Thifensulfuron:tribenuron had no effect on either crop at rates less than 3.3% X. Two weeks after application of thifensulfuron:tribenuron, 10% X, and to a lesser degree 3.3% X rates, caused newly emerged leaves to become chlorotic, reducing chlorophyll content 25 to 50%. These treatments also reduced net photosynthesis by 37% and reduced or halted growth of the main stem. Early formation of leaves was reduced, thus tripling light penetration through the canopy. Five to six weeks after application, 10% X thifensulfuron:tribenuron had, in some treatments, more than tripled branching in pea, more than quadrupled branching in lentil, and reduced biomass as much as 42%. Flowering and maturity were delayed. Plants recovered from stunting by thifensulfuron:tribenuron to varying degrees depending on environmental conditions, and final seed yield generally was reduced less than 25%. In controlled greenhouse experiments, rate response to thifensulfuron generally was similar to that observed in field experiments. Pea was stunted less at 30 C than at 10 C, whereas lentil was affected similarly at these temperatures. Overall, visual symptoms from thifensulfuron:tribenuron exposure were more pronounced in pea than in lentil and were detectable at levels substantially lower than those that affected final seed yields.