Selectivity of herbicides in the post-emergence sugarcane seedlings in primary selection fields

摘要

The hypothesis here proposed is that, in primary fields of mass selection (F 1 ) of sugarcane, herbicides exert a selective action when applied in the early post-emergence of seedlings (POST -i ) and supplemented after their establishment phase (POST -l ) even in sandy soils. To verify such hypothesis, the selectivity of herbicides was studied on seedlings of three sugarcane families, after their application both at early and late post-emergence in primary selection fields (F1). The field had a randomized blocks design, with five replications, and the subdivided plots scheme was used. Twelve herbicide treatments were allocated in the plots (27 m -2 ), whereas the sub-plots (9 m -2 ) contained three families of seedlings. Each sub-plot consisted of a transplanted row (0.5 x 1.50 m) with 12 individuals of the same family. Six treatments were employed, namely, T1: tebuthiuron (1200 g ha -1 ) post -i + ametryn (3000 g ha -1 ) post -l ; T2: diuron (1404 g ha -1 ) + hexazinone (396 g ha -1 ) post -i + ametryn (3000 g ha -1 ) post -l ; T3: sulfentrazone (800 g ha -1 ) post -i + ametryn (3000 g ha -1 ) post -l ; T4: diuron (1404 g ha -1 ) + hexazinone (396 g ha -1 ) post -i + metribuzin (1920 g ha -1 ) post -l ; T5: sulfentrazone (800 g ha -1 ) post -i + metribuzin (1920 g ha -1 ) post -l , and T6: weeded plot. The sugarcane families were: F400 ( ♀ IAC086155 x ♂ unknown), F43 ( ♀ IACBIO264 × ♂ IAC911099), and F14 ( ♀ IACSP991305 × ♂ GlagaH). We concluded that the herbicides tebuthiuron (1200 g ha -1 ), diuron (104 g ha -1 ) + hexazinone (396 g ha -1 ), or sulfentrazone (800 g ha -1 ), when applied in the early post-emergence and supplemented with ametryn (3000 g ha -1 ) or metribuzin (1920 g ha -1 ) in late post-emergence (60 days from planting) of the sugarcane families studied, were selective to the seedlings. That is, no toxicity symptoms with a potential to impede the final selection of seedlings occurred.