Managing Tropical Spiderwort (Commelina benghalensis) In

Roundup Ready Cotton

A.S. Culpepper, J.T. Flanders, and A.C. York

University of Georgia and N. C. State

Spiderwort response to Roundup UltraMax*

20 oz 0 oz 30 oz 0 oz

40 oz 0 oz 50 oz 0 oz*Pictures 15 d after treatment. No plants died from any treatment. Six inch at time of application.

Typical RR Cotton Grower Program:

1) DNA at planting

2) Roundup at 3- to 4-leaf

3) Roundup at layby

Tropical Spiderwort Infestation

Red = severeOrange = moderateGreen = lightYellow = exist Gray = not found

2002 Prostko agent survey

Spiderwort’s Rank as Georgia’s Most Troublesome Weeds in Cotton

1998: not ranked*

2001: ninth*

2003: number 1

*Published in SWSS annual proceedings.

Tropical spiderwort infestation, Cairo, GA, 2001.

Grady Co. 2002

Objectives

Compare POST over-the-top herbicide options for spiderwort control

Compare POST-directed herbicide options for spiderwort control

Develop a systems approach for spiderwort management

*

Location

Two on farm trials in 2001 and 2002

***

Materials and Methods

Cultivar: various RR cultivars

Planted: May or June

Plot size: three or four rows by 30 feet

Design: split plot

Treatments: factorial arrangement with 3 early

POST by 8 directed options

Reps: 3 or 4 reps

Application Information

DNA applied at planting at each location

POST over-the-top treatments applied at 15 GPA

POST directed treatments applied at 15 to 20 GPA

Treatments applied at 3 MPH

Tropical spiderwort 1 to 4 inches, avg. 2 to 3 inch

Weed control visually estimated throughout season

POST Over-the-Top: Whole Plot

1. Roundup UltraMax (0.75 lb ae)

2. Roundup + Staple (0.032 lb ai)

3. Roundup + Dual Magnum (0.95 lb ai)

0

20

40

60

80

100

RU + Staple + Dual

21 DAT

Tropical Spiderwort Control with Topical Applications.

53 c60 b

80 a

% c

ontr

ol

UltraMax @ 4 leaf cotton + Dual Magnum 1 pt/A

1) Dayflower emerged 3 to 7 day after 4 leaf application. One inch of rain within 48 hr.

2) Prowl applied PRE. No layby.

0

20

40

60

80

100

RU + Staple + Dual

21 DAT

Late-season*

Tropical Spiderwort Control with Topical Applications.

49 b 48 b

69 a

% c

ontr

ol

53 c60 b

80 a

*Late-season control pooled over directed applications.

POST Directed Treatments: Subplot

1. Roundup UltraMax (0.75 lb ae)

2. + Direx (0.625 lb ai)

3. + Valor (0.032 lb ai)

4. + Aim (0.012 to 0.016 lb ai)

5. + Harvade (0.3 lb ai)

6. MSMA (2 lb) + NIS

7. + Direx (1 lb ai)

8. + Valor (0.064 lb ai)

Timely & precise applications were made with less than 9% herbicide injury noted.

Mid-Season Tropical Spiderwort Control with Directed Applications (21 DAT).

0

20

40

60

80

100

70 e

80 bcd

% c

ontr

ol

Roundup

+ Aim

+ Direx

+ Harvade

+ Valor

MS

MA

+ Direx

+ Valor

Data pooled over four locations. Directed main effect means presented.

79 bcd 75

de

85 ab 78

cd

83 abc

89 a

Prowl pre, glyphosate POST, glyphosate directed. 17 day after directed.

Prowl pre, glyphosate POST, MSMA directed. 17 day after directed.

Late-Season Tropical Spiderwort Control with Directed Applications.

0

20

40

60

80

100

44 c 42 c

80 a

% c

ontr

ol

Roundup

+ Aim

+ Direx

+ Harvade

+ Valor

MS

MA

+ Direx

+ Valor

Data pooled over four locations. Directed main effect means presented.

57 b

43 c

64 b

45 c

64 b

76 a

Four Most Effective Spiderwort Systems at Harvest. Pooled over 4 locations.

Herbicide system Control (%)

Herbicide cost ($/A)

Prowl, RU + Dual, Valor + MSMA 80 35.23

Prowl, RU + Dual, Direx + MSMA 75 29.57

Prowl, RU + Dual, Roundup + Direx 78 29.58

Prowl, RU + Dual, Roundup + Valor 73 31.93

Conclusions

1) Early POT applications of glyphosate + Staple are more effective than glyphosate alone on emerged spiderwort.

2) However, residual control from Dual appears to be more critical in the system.

Conclusions

3) MSMA was more effective than glyphosate at layby.

4) Direx and Valor were the most effective directed tank mix options due to residual spiderwort activity.