Glyphosate hinders purple nutsedge (Cyperus rotundus) and yellow nutsedge (Cyperus esculentus) tuber production

The phase-out of methyl bromide requires alternative nutsedge management options in vegetable systems. Options that target tuber production, the primary means of reproduction, will be most beneficial. A study was conducted to evaluate the response of purple nutsedge and yellow nutsedge foliar growth and tuber production to a range of glyphosate rates. Glyphosate was applied at six rates between 0.41 and 2.57 kg ae ha(-1) to 5-wk-old nutsedge plants with multiple shoots. The rate of glyphosate needed to reduce growth 50% (I(50)) was similar for purple nutsedge foliar growth (0.58 kg ha(-1)) and tuber biomass (0.55 kg ha(-1)). In contrast, I(50) for yellow nutsedge foliar growth was 0.73 kg ha(-1) which was greater than the I(50) for tuber biomass (0.41 kg ha(-1)). First-order tubers, those directly attached to the initial tuber, had an I(50) of 0.70 and 0.44 kg ha(-1) of glyphosate for purple nutsedge and yellow nutsedge tuber biomass, respectively. For all higher-order tubers, I(50) values ranged from 0.29 to 0.60 and 0.14 to 0.30 kg ha(-1) of glyphosate for purple nutsedge and yellow nutsedge tuber biomass, respectively. Glyphosate at 0.74 kg ha(-1) prevented fourth-order purple nutsedge and third-order yellow nutsedge tuber production (terminal tubers for yellow nutsedge). Fifth- and sixth-order purple nutsedge tuber production was eliminated by the lowest tested rate of glyphosate (0.41 kg ha(-1)). Effective nutsedge management options will require consistent control between spring and autumn crops. Glyphosate is economical, poses no herbicide carryover issues to vegetables, and minimizes nutsedge tuber production; therefore, it is a suitable candidate to manage nutsedges.