Effects of Glyphosate on Tuber Sprouting and Growth of Purple Nutsedge (Cyperus rotundus)1

Abstract

A study was conducted to determine the dose–response of purple nutsedge tuber sprouting and plant growth to glyphosate. Tuber sprouting on day 6 satisfactorily fitted the probit model, with a predicted effective dosage causing 50% inhibition of response (ED50) of 30 mM, which is similar to that with 25 mM of ED50 on day 3. In addition, together with the dose–response analysis of bud growth on day 6, it was shown that bud growth of purple nutsedge was more sensitive to root- or tuber-absorbed glyphosate or both than was tuber sprouting; the former had 1.25 mM of ED50. During the V1–2 stage, purple nutsedge injury, including shoot dehydration, wilting, and yellowing, appeared sequentially when glyphosate was absorbed. When compared with the dose–response of shoot greenness of purple nutsedge at the V5–7 stage under the root-absorbed glyphosate treatment, purple nutsedge at the V1–2 stage was less sensitive to root-applied glyphosate. Further studies for determining the efficacy of glyphosate applied on root and foliage of purple nutsedge at the V5–7 stage showed that injury from glyphosate occurred within 7 d after foliar treatment, and the ED50 values of glyphosate for shoot survival and leaf chlorophyll were 13.1 and 14.5 mM, respectively. However, the response of plants was less sensitive to root-absorbed glyphosate, which had an ED50 of 101 mM. This finding might be the result of direct injury of roots caused by glyphosate, resulting in the delayed and diluted effect of this herbicide from root to shoot.Nomenclature: Glyphosate; purple nutsedge, Cyperus rotundus L. #3 CYPRO.Additional index words: Dose–response, growth, young plant.Abbreviations: DAT, days after treatment; ED50, effective dosage causing 50% inhibition of response; EPSPS, 5-enol-pyruvyl-shikimate-3-phosphate synthase (EC 2.5.1.19).