Abstract

Glyphosate, 2,4-D, imazethapyr and paraquat + diuron were studied in greenhouse experiments at four application rates in order to evaluate their effects on white clover (Trifolium repens L.) growth and aerial shoot injury at three different phenological stages. Herbicide-induced foliar injury on white clover ranged from no symptoms to early chlorosis, leaf necrosis, stunted growth and death depending on herbicide rate and white clover phenological stage. Imazethapyr showed the highest selectivity at the three-leaf trifoliate stage. Seedlings treated with glyphosate at 1080 g a.i. ha^-1, however, were dead at 21 days after application (DAA). White clover herbicide tolerance increased with plant age, and selectivity was found to be affected as herbicide rate increased. Paraquat + diuron caused the highest levels of white clover phytotoxicity and plant death. The herbicides studied showed potential to be used as selective products on white clover depending on their rates, as well as the timing of their application onto white clover depending furthermore, on the specificity weeds infesting white clover fields.

Key words: Glyphosate, 2,4-D, Paraquat + diuron, Imazethapyr, Trifolium repens.