managing tropical spiderwort ( commelina benghalensis) in roundup ready cotton
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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.
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