Effect of Growth Stage and Application Site on Tolerance of Rice (Oryza sativa) to Haloxyfop

Abstract

Greenhouse experiments were conducted to evaluate seedling rice tolerance to haloxyfop and to determine soil moisture effects on root, shoot, and root plus shoot uptake. Visible injury to rice at 4 wk after treatment increased with each increase of haloxyfop rate from 40 to 160 g ai/ha, regardless of growth stage. Less injury was observed at equivalent rates in four-leaf than in younger rice. Similarly, equivalent haloxyfop rates reduced shoot fresh weight of one- to three-leaf rice more than shoot fresh weight of four-leaf rice. There was no interation between soil moisture levels (19 and 24%) and haloxyfop activity. Fresh weights were less when haloxyfop at 40 or 80 g/ha was absorbed by both roots and shoots than when absorption was by either roots or shoots alone. However, at 80 g/ha fresh weight was similar whether haloxyfop was absorbed by roots or shoots alone. Root uptake, in the presence of 160 g/ha haloxyfop, did not contribute to reduced fresh weight with root plus shoot treatments because of the initial foliar activity incurred.