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

Abstract

The hypothesis here proposed is that, in primary fields of mass selection (F1) 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.