SUNFLOWER RESISTANCE TO ACETOLACTATE SYNTHASE-INHIBITING HERBICIDES

Abstract

Sunflower is very sensitive to herbicides applied in post-emergence to control broad-leaf weeds. Researchers have developed herbicide-resistant genotypes to imidazolinone herbicides. This study aimed to evaluate the selectivity of imidazolinone and sulfonylurea herbicides applied on sunflower plants (Tera 8003 and Tera 8011) resistant to acetolactate synthase-inhibiting herbicides. The experiments were conducted at Embrapa Gado de Leite, in Coronel Pacheco, Minas Gerais State, and Valença, Rio de Janeiro State, Brazil. The experimental design was randomized complete blocks, with four replications. The treatments consisted of hoed control, imazapyr 25 g a.i. ha^-1 and 50 g a.i. ha^-1, imazethapyr 70 g a.i. ha^-1 and 100 g a.i. ha^-1, nicosulfuron 20 g a.i. ha^-1 and 32 g a.i. ha^-1, and chlorimuron 7.5 g a.i. ha^-1 + 0.05% v/v of mineral oil. The crop injury percentage, chlorophyll content (SPAD index), plant height, dry matter production and percentage, and yield were evaluated. The imazethapyr doses (70 g a.i. ha^-1 and 100 g a.i. ha^-1) were the most selective ones, the nicosulfuron dose (20 g a.i. ha^-1) showed moderate tolerance, and imazapyr and chlorimuron caused greater injury, for both sunflower hybrids.