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   Home » Resistance » Control Options for Group II Resistant Weeds in Soybean

Control Options for Group II Resistant Weeds in Soybean

Mike Cowbrough, OMAFRA - Guelph
Francois Tardif, University of Guelph
Peter Sikkema, Ridgetown College, University of Guelph

1) Eastern Black Nightshade

Weed Staging: Weeds had not emerged for the pre-emergent (pre) treatments and were at the 4-leaf stage at the time of application for the post-emergent treatments.

Table 1. Group II resistant eastern black nightshade control, the range in control over two years, and the timing and product rate of various herbicide programs.

Product (Timing and Rate per acre)

Control (%)

Range (%)

Axiom (pre - 0.34 kg/ac)

83

70-95

Broadstrike Dual Magnum (pre - 0.624 L/ac)

85

78-91

Dual II Magnum (pre - 0.7 L/ac)

85

76-93

Frontier (pre - 0.56 L/ac)

81

70-91

Dual II Magnum (pre - 0.7 L/ac) + Blazer (post - 1 L/ac)

95

90-99

Dual II Magnum (pre - 0.7 L/ac) + Reflex (post 0.4 L/ac)

97

94-99

Lorox L (pre- 1.87 L/ac)

99

99

Blazer (post - 1 L/ac)

80

68-99

Reflex (post - 0.4 L/ac)

83

73-98

Bottom Line: There are numerous products that will provide over 80% control of eastern black nightshade. In general, the level of control is proportional to the herbicide program's cost. Applications of Lorox L, Dual II Magnum followed by Blazer or Reflex provided the best and most consistent control of eastern black nightshade, but are also the most expensive.

2) Common Cocklebur

Weed Staging: Weeds were between the cotyledon and 5-leaf stage at the time of application.

Table 2. Control of group II resistant common cocklebur and the timing and product rate of various herbicide programs.

Product (Timing and Rate per acre)

Control (%)

Basagran Forté (post - 0.9 L/ac) 92
Blazer (post - 1 L/ac) 91
Reflex (post - 0.4 L/ac) 63

One field trial conducted by Peter Sikkema in 2001.

Bottom Line: Both Blazer and Basagran Forté provide good control of common cocklebur.

3) Pigweed Species

Weed Staging: Weeds had not emerged for the pre-emergent (pre) treatments and were up to the 10-leaf at the time of application for the post-emergent treatments.

Table 3. Control of group II resistant pigweed and the timing and product rate of various herbicide programs.
Product (Timing and Rate per acre)

Control (%)

Blazer (post - 1 L/ac)

78

Blazer (post - 0.5 L/ac + Assist Oil)

69

Broadstrike Dual II Magnum (pre - 0.624 L/ac)

99

Boundary (pre - Dual II Magnum (0.54 L/ac) + Sencor (0.27 kg/ac))

99

Frontier (pre - 0.56 L/ac)

99

Lorox L (pre - 1.87 L/ac)

99

Reflex (post - 0.4 L/ac)

59

Sencor 75 DF (pre - 0.3 kg/ac)

99


One field trial conducted by Peter Sikkema in 2002.

Bottom Line: The post-emergent herbicides have tended to provide inconsistent control of pigweed. Therefore, a soil applied herbicide program should be used to target group II resistant pigweed.

4) Common Ragweed

Weed Staging: Weeds had not emerged for the pre-emergent (pre) treatments and were up to 10-leaf stage at the time of application for the post-emergent treatments.

Table 4. Group II resistant common ragweed control, the range in control over two years, and the timing and product rate of various herbicide programs.

Product (Timing and Rate per acre)

Control (%)

Range (%)

Axiom (pre - 0.34 kg/ac)

54

18-91

Boundary (pre - 0.54 L/ac Dual + 0.27 kg/ac Sencor)

64

8-97

Boundary (pre) + Blazer (post - 1 L/ac)

78

18-99

Boundary (pre) + Reflex (post - 0.4 L/ac)

83

38-99

Lorox L (pre - 1.87 L/ac)

83

68-96

Sencor 75 DF (pre - 0.3 kg/ac)

64

4-90

Blazer (post - 1 L/ac)

51

35-79

Reflex (post - 0.4 L/ac)

85

75-99


A summary of 4 trials conducted by Peter Sikkema in 2002 and 2003.

Bottom Line: Although not incredibly common, populations of triazine resistant common ragweed do exist. Therefore, products that contain metribuzin (i.e. Boundary, Sencor) will not control common ragweed. Furthermore, it would appear that when metribuzin is applied to triazine resistant common ragweed, "rescue" treatments with Blazer or Reflex have been ineffective. This may be because the weeds have been "hardened off" by the initial metribuzin application. If you are confident that triazine resistance is not an issue, then Boundary alone or Boundary followed by Reflex will provide good control of common ragweed. If common ragweed is both resistant to triazine and group II herbicides, then a post-emergent application of Reflex will provide the most consistent level of control.

5) Green Foxtail

Weed Staging: Weeds had not emerged for the pre-emergent (pre) treatments and were up to the 4-leaf stage at the time of application for the post-emergent treatments.

Table 5. A two-year average of group II resistant green foxtail control, the range in control over two years, and the timing and product rate of various herbicide programs.

Product (Timing and Rate per acre)

Control (%)

Range (%)

Axiom (pre - 0.5 kg/ac)

80

75-84

Dual II Magnum (pre - 0.7 L/ac)

87

78-96

Frontier (pre - 0.56 L/ac)

97

96-97

Poast (post - 0.19 L/ac)

99

99


A summary of 2 trials conducted by François Tardif in 2002 and 2003.

Bottom Line: Any of the soil applied grass herbicides will provide good control of group II resistant green foxtail. Alternatively post-emergent grass herbicides (i.e. Poast) will also provide good control of green foxtail.

6) Common Lamb's-Quarter

Weed Staging: Weeds were at the 4-leaf stage at the time of application for the post-emergent treatments.

Table 6. Control of group II resistant common lamb's-quarter's, the range in control over two years, and the timing and product rate of various herbicide programs.

Product (Timing and Rate per acre)

Control (%)

Basagran Forté (post - 0.9 L/ac)

99

Blazer (post - 0.5 L/ac + Assist Oil )

50

Reflex (post - 0.4 L/ac)

32

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