Effects of growth stage on translocation of glyphosate in quack grass

Visual symptoms of toxicity (inhibition of leaf growth and bud germination) were used to study the influence of growth stage of quack grass (Agropyron repens (L.) Beauv.) on glyphosate (N-phosphonomethyl glycine) transport and efficiency. Glyphosate (or a toxic metabolite) moved in sufficient quantity from the point of application on the leaf within 1 day to significantly affect the regrowth and within 2 days to affect the regenerative potential of rhizomes. As quack grass plants developed to the four-leaf stage the effect of glyphosate treatment increased. When only one shoot was sprayed on a rhizome supporting two shoots at the same leaf stage, glyphosate inhibited leaf growth on the untreated shoot at the two-leaf stage but not at the four-leaf stage. Similarly, glyphosate inhibited leaf growth on tillers when only the main shoot was sprayed. However, when only the tiller was sprayed, leaf production was not affected on the main shoot suggesting that glyphosate is phloem mobile.