The toxicity of oil herbicides to Paspalum dilatatum POIR. 2. The effect of light on toxicity.

Abstract

The influence of light on the phytotoxicity of hydrocarbon oils was investigated by exposing the oils to light before and after application to a perennial grass, Paspalurn dilatatum Poir. Exposure of the oils to light and air for a month prior to spraying slightly increased the speed of contact injury to foliage but did not affect regrowth. Oils had a contact effect on foliage only in the presence of light. Shading the plants for one week following treatment delayed the development of contact injury and resulted in greater inhibition of regrowth (toxicity). The increase in toxicity following shading is ascribed to the delay in contact effect per se. The results suggested an antagonism between speed of contact injury and inhibition of regrowth. Supporting evidence was provided by an additional experiment in which fortifying agents were added to the oils. Fortifying agents increased speed of foliage kill but in no instance was toxicity increased. When power kerosene was used the addition of fortifying agents reduced toxicity.