INFLUENCE OF GROWTH STAGE ON SPRING BARLEY (HORDEUM-VULGARE) TOLERANCE TO CHLORSULFURON

Tolerance of barley to chlorsulfuron at various stages of crop develop ment was studied in weed-free field and pot experiments. Five barley c rops were sown between mid-May and mid-july in the field in 1988 and s prayed simultaneously with four rates of chlorsulfuron when the corres ponding stages of crop development ranged from growth stage 7 (GS 7) t o GS 31. Early-sown barley yielded more than late-sown barley, but per cent grain yield reduction from chlorsulfuron was similar for all plan ting dates. In a field experiment in 1989, barley was sown at three da tes (May, June, and July) and each was treated with chlorsulfuron at 0 , 15, 30, and 60 g ai ha-1 at either GS 12 or GS 15. Grain yield of ba rley sown in May and treated with 15 g ha-1 chlorsulfuron at GS 12 was reduced 35%, compared with no effect when applied at GS 15; this yiel d reduction was related to spike size and number. Application of chlor sulfuron at GS 12 and GS 15 to barley sown in June caused yield reduct ions of 20 and 11%, respectively. In contrast, barley sown in mid-July was not affected by chlorsulfuron. Applications of chlorsulfuron at G S 12, 13, 14, and 15 led to reductions of 75, 35, 15, and 5% shoot dry matter (DM) of plants grown in pots and measured at GS 33. Root DM wa s more sensitive to chlorsulfuron than shoot DM. Tolerance of barley t o chlorsulfuron increased with age of the plant at the time of applica tion.