The ALS-inhibiting herbicides are highly effective when applied in low rates, presenting low toxicity to mammalians, wide control spectrum and, some of them, long soil persistence. Usually, the resistance mechanism for ALS inhibitors is due to the lack of enzyme sensitivity to the herbicide, resulting from alterations in the enzyme conformation. However, crop tolerance mechanisms are observed, such as differences in absorption, translocation and degradation before the herbicide reaches the target site. The objective of this research was to evaluate aspects related to the level and main absorption mechanism of pyrazosulfuron-ethyl to determine the resistance mechanism of an ALS-resistant S. montevidensis ecotype. Experiments were carried out under growth chamber, and greenhouse conditions. The treatments were 2(0)x; 2²x; 2(4)x; 2(6)x and 2(8)x (X=label rate) of pyrazosulfuron-ethyl (20 g a.i. ha-1), applied individually on the shoots, roots and seeds of a resistant and a susceptible ecotype. The results showed some differences between susceptible and resistant ecotypes in relation to the main site of herbicide absorption.
resistance mechanisms; giant arrowhead; translocation
