ISSUE 7   June 24, 2010

VOLUNTEER RR SOYBEAN CONTROL

Many fields have volunteer RR soybean. Many have asked how much Stinger (clopyralid) does it take to "really" control soybean with no regrowth. After some encouragement from one of our illustrious crop consultants, we quickly planted soybean in the greenhouse and at on June 24th when the soybean were unifoliate to 1st trifoliate stage. The following treatments were applied.

 

Rate per acre

Whole soybean plant

Soy leaves

10 DAA

14 DAA

14 DAA

COC

MSO

COC

MSO

COC

MSO

---------------------- % death --------------------

Stinger

1 fl oz

70

70

70

70

12

10

Stinger

2 fl oz

70

70

70

70

23

15

Stinger

3 fl oz

70

70

80

80

57

67

Stinger

4 fl oz

70

70

80

80

65

93

LSD (0.05)

 

na

na

5

5

9

9

By 10 days following application, no differences in treatments could be determined. An overall control rating of 70% was recorded but all growth had ceased and no plants resumed growth from buds in leaf axils. Even as of today’s date (Jun 22), no regrowth has occurred. Only the 3 or 4 fl oz/A rate with MSO caused plants to completely desiccate. In all other treatments, the growing points appeared dead but the leaves maintained their normal green color with no phytotoxicity showing. So, how dead do you need the plants to be? How much money are you willing to spend to "kill" soybean by using Stinger (clopyralid)? From this data, the 1 fl oz/A rate stopped plants from continuing to grow after application but did not cause "crispy" dead plants. Only the higher rates with the more aggressive MSO adjuvant "killed" soybean plants.

 

VOLUNTEER RR CANOLA CONTROL

Page 115 in the ND Weed Control Guide shows control of volunteer RR canola, corn, and soybean from selected herbicides. Much more information is need to complete this chart as not all herbicides are listed and data is lacking on later crop growth stages. Experiments were established this spring to study volunteer RR canola control from herbicides applied at the:

3.2 growth stage = flower cluster raised above the rosette
4.1 growth stage = 10-20% flowering

These stages are later than those listed in the weed guide. The 3.2 growth stage experiment was evaluated at 14 daa (days after application) with the following results.

Herbicide

Rate per acre

Vol. RR canola

14 DAA

- % control -

FirstRate

0.2 oz

50

0.3 oz

60

Flexstar

0.5 pt

99

 

0.75 pt

99

Cadet

0.7 fl oz

10

 

0.9 fl oz

20

Sharpen

1 fl oz

95

Ignite

22 fl oz

60

 

33 fl oz

70

Extreme

1.5 pt

50

Raptor

2 fl oz

50

 

4 fl oz

60

The 14 daa evaluation is preliminary as control could change for the better for most of the systemic herbicides. It appears that Flexstar and Sharpen had the most activity on bolted canola but the residue from Flexstar could interfere with rotation of some crops, like sugarbeet. Later evaluations will be made and results from the study where applications were made at the 4.1 growth stage will also be compiled.

Rich Zollinger
NDSU Extension Weed Specialist
r.zollinger@ndsu.edu


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