NDSU Crop and Pest Report
Weeds


ISSUE 12  July 17, 2003

PERENNIAL SOWTHISTLE AND CANADA THISTLE CONTROL

Dr. Rod Lym, NDSU Weed Scientist, Perennial/Noxious Weeds, has submitted the following information on control of perennial sowthistle and Canada thistle. For additional information see ND Weed Control Guide, pages 56-57, and paragraph T2 on page 102.

Ally continues to be the treatment of choice for perennial sowthistle control in crop. Ally XP at 1/10 oz/A applied in cropland provided nearly 100% perennial sowthistle control 1 and 12 months after treatment (MAT) (Table 1). Canada thistle control was also acceptable and averaged 84% the following growing season. The addition of Harmony Extra XP did not alter either perennial sowthistle or Canada thistle control. Curtail at 2 pints/A provided 94% perennial sowthistle control 12 MAT but only 73% Canada thistle control and cost approximately $9/A compared to $2/A for Ally XP.

In a separate study, post-harvest application of glyphosate provided excellent Canada thistle control the following growing season (Table 2). Express, Harmony Extra, and Curtail M provided approximately 95% Canada thistle control in wheat during the cropping season. However, control declined to approximately 70% the following spring with Express or Harmony Extra and to 51% with Curtail M if these treatments were not followed by post-harvest glyphosate. Canada thistle control averaged nearly 100% the following spring when glyphosate was applied either at 1 or 2 qt/A in the fall regardless if a herbicide had been applied during the previous cropping season or not.

Table 1. Control of perennial sowthistle and Canada thistle in cropland.

Treatment

Rate

Control

Cost

1 MATa

12 MATa

PESTb

CTc

PESTb

CTc

 

Product/A

% control

$/A

Ally XP

1/10 oz

100

87

99

84

2

Ally XP + H. Extra XP

1/20 + 1.5/10 oz

97

85

96

80

3

Ally XP + H. Extra XP

1/10 + 3/10 oz

99

81

98

68

5

Curtail

2 pints

96

76

94

73

9

Glyphosate

1 pint

65

24

55

10

4

LSD (0.05)

 

9

12

10

18

 

a Months after treatment.
b Perennial sowthistle
c Canada thistle.

 

Table 2. Control of Canada thistle in wheat.

Treatment

Rate

Wheat

Canada thistle

Cost

7 DATa

21 DATa

2 MATb

12 MATb

Spring

Fall

Product/A

% injury

% control

$/A

Express XP

Glyc

1/6 oz

1 qt

1

71

94

99

12

Express XP

Glyc

1/6 oz

2 qt

0

78

98

99

21

Express XP

Glyc

1/3 oz

2 qt

1

85

98

99

24

Express XP

-----

1/3 oz

0

1

81

94

63

6

H. Extra XP + 2,4-D

Glyc

3/10 oz+3/4 pt

2 qt

3

76

94

98

23

H. Extra XP + 2,4-D

Glyc

6/10 oz+3/4 pt

2 qt

3

89

95

99

26

H. Extra XP + 2,4-D

----

6/10 oz+3/4 pt

0

4

86

98

74

8

H. Extra XP

----

6/10 oz

0

3

85

97

70

7

Curtail M

Glyc

2 pt

2 qt

2

94

98

97

29

Curtail M

----

2 pt

0

1

96

96

51

11

None

Glyc

-----

2 qt

0

0

0

99

18

LSD (0.05)

 

1

21

7

9

 

a Days after treatment (spring).
b Months after spring treatment (spring).
c Glyphosate formulation was Roundup Ultra Max and was applied Sept. 26, 2002.

Richard Zollinger
NDSU Extension Weed Specialist
rzolling@ndsuext.nodak.edu

 


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