Effect of 2,4-D ester on the nitrate concentration of variegated thistle (Silybum marianum) (L.) Gaertn

Abstract

The effect of 2,4-D ester application on the nitrate concentration of variegated thistle (Silybum marianum) was investigated in pot and nutrient solution experiments. In general, the nitrate concentration of sprayed plants increased significantly 1-2 days after 2,4-D application. The effect lasted for up to 4 days before the nitrate concentration returned to the prespraying levels. In a pot experiment, this increase in plant nitrate concentration was only observed at the higher of 2 applied nitrate levels (i.e. 15 m.e./L). In a third experiment, the nitrate concentration of naturally occurring variegated thistles varied from 66 to 17152 ¦g/g. There was a strong correlation (r = 0.92) between thistle nitrate concentration and the nitrate level in the soil directly beneath the sampled plant. The results are discussed in relation to their implication for avoiding nitrate toxicity in livestock grazing variegated thistle, especially after the thistles have been treated with 2,4-D.