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 (AN)

Biomass accumulation most common parameter to describe competitiveness

Biomass accumulation directly linked with AN

50% reduction in AN 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 CO2 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 AN

020406080

100120140

0 2 4 6 8 10 12

days

AN (

% o

f c

on

tro

l)

glyphosate

imazapic

halosulfuron

Error bars = LSD(0.05)

Effect of Herbicide on AN

-10

10

30

50

70

90

110

130

0 2 4 6 8 10 12

days

AN (

% o

f c

on

tro

l)

MSMA

bentazon

Error bars = LSD(0.05)

AN50 Values

Herbicide

Rate

(g ai ha-1)

AN50

(days)

Glyphosate 840 3.2 b

Halosulfuron 70 1.6 a

Imazapic 70 2.1 a

MSMA 2200 3.3 b

Bentazon 840 --

Regrowth Biomass

Herbicide

Rate

(g ai ha-1)

AN50

(days)

Regrowth

(g)

Glyphosate 840 3.2 b 2 a

Halosulfuron 70 1.6 a 0 a

Imazapic 70 2.1 a 0 a

MSMA 2200 3.3 b 5 a

Bentazon 840 -- 44 b

Bentazon recovery

• Label suggests bentazon should be applied sequentially (7-10d) for CYPER control.

• Pattern of AN decline and recovery 5 DAT has been observed in rice. Recovery was attributed to metabolism 85% metabolism observed 4 DAT

Effect of Herbicide on gs

020406080

100120140

0 2 4 6 8 10 12

days

gs

(% o

f c

on

tro

l)

MSMA

glyphosate

halosulfuron

imazapic

Error bars = LSD(0.05)

MSMA and gs

• 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

• gs highly correlated with AN, except for MSMA

Any Questions?