Duration of yellow nutsedge competitiveness after treatment with various herbicides J. A. Ferrell*, H. J. Earl, W. K. Vencill University of Georgia

CYPER Competition C4 perennial that reproduces vegetatively Higher photosynthetic rate than most crop species. Yield reductions between 59 and 87% for corn, rice, and soybeans. Alternate host for pathogens.

Objectives Determine time required for glyphosate, bentazon, imazapic and halosulfuron to render SORHA physiologically noncompetitive

Physiologically non-competitive 50% reduction in net carbon assimilation (A N )  Biomass accumulation most common parameter to describe competitiveness  Biomass accumulation directly linked with A N  50% reduction in A N was a comparative indicator of competitiveness

Materials and Methods CYPER grown in greenhouse for 20 wk Herbicide Treatments  Glyphosate 840 g ai ha -1  Halosulfuron 140 g ai ha -1 + NIS  Imazapic 70 g ai ha -1 + NIS  MSMA 2200 g ai ha -1 + NIS  Bentazon 840 g ai ha -1 + COC Plants treated at ~25 cm

CYPER plants before treatment

Materials and Methods Photosynthesis and Stomatal Cond.  Li-Cor 6400  PPFD = 1200 µmol m -2 s -1  CO 2 concentration (sample side) = 360 µmol mol -1

Materials and Methods Experiment conducted twice Randomized Complete Block Design with 5 replications All data normalized to the control The data were pooled across runs

Effect of Herbicide on A N Error bars = LSD(0.05)

Effect of Herbicide on A N Error bars = LSD(0.05)

A N50 Values Herbicide Rate (g ai ha -1 ) A N50 (days) Glyphosate b Halosulfuron701.6 a Imazapic702.1 a MSMA b Bentazon840--

Regrowth Biomass Herbicide Rate (g ai ha -1 ) A N50 (days) Regrowth (g) Glyphosate b2 a Halosulfuron701.6 a0 a Imazapic702.1 a0 a MSMA b5 a Bentazon b

Bentazon recovery Label suggests bentazon should be applied sequentially (7-10d) for CYPER control. Pattern of A N decline and recovery 5 DAT has been observed in rice.  Recovery was attributed to metabolism  85% metabolism observed 4 DAT

Effect of Herbicide on g s Error bars = LSD(0.05)

MSMA and g s MSMA possibly inhibits the malic enzyme in C4 plants (Knowles and Benson 1983). Accumulation of malic acid may lead to photooxidative damage (Devine et al. 1993). Hypothesis Cellular leakage, leading to guard cell dysfunction, resulted in unregulated water losses via stomata. Compromised cuticular integrity caused water loss from epidermal cells.

Conclusions Halosulfuron and imazapic renders CYPES physiologically non-competitive more quickly than glyphosate, MSMA, or bentazon. A single application of bentazon did not control CYPES g s highly correlated with A N, except for MSMA

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