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Pokeweed Management In Field Crops:An Update

Post emergence herbicide options for corn and soybeans.

Pokeweed populations have been on the rise in Pennsylvania field crops. There may be several reasons for this, including the increase in no-till acres where plowing used to control or suppress pokeweed, and secondly due to the reduction in the use of soil residual herbicides, particularly in soybean (because of Roundup Ready) and perhaps lower atrazine use rates in corn. Kelly Patches is starting her second year of her Master’s degree researching pokeweed management in no-till corn and soybean. Her work has been funded in part by the Pennsylvania Soybean Board, and we graciously thank them for their support.

The first thing to remember is that since pokeweed is a perennial, effective options for suppression or control are focused on POST herbicides in corn and soybean. During the summer of 2012, herbicide efficacy experiments were conducted in both these crops. Results from the corn and soybean studies show that glyphosate seems to be a key component in controlling pokeweed. Although Roundup Powermax® was the formulation of glyphosate used in these experiments, other brands should perform similar at the same application rate. Also, combinations of herbicides seem to work better than individual herbicides alone. Residual herbicides, such as atrazine, may also play an important role, as new seedlings emerged into late summer. Both the corn and soybean herbicide efficacy studies will be repeated this summer.  Keep in mind that these ratings are for end of season control and that longer-term control (e.g. year after application) is not considered.  We are currently collecting those data.  Here is a quick summary of last year’s results.

Corn herbicides

The corn herbicide efficacy trial was conducted in a field near Mt. Joy, Lancaster County, PA. Nine POST treatments were evaluated in Roundup Ready® corn (See Table 1.) The pokeweed ranged from seedling to an average of 3 feet tall at the time of application. All herbicide treatments provided at least 79% control, while atrazine + Callisto® and Roundup® + Permit® + Status® provided the highest control (91%). All herbicide treatments also provided at least 87% reduction of above-ground dry weight, while Status®; Callisto® + atrazine; and Roundup® + Permit® + Status® all provided above 95% reduction in dry weight.

Table 1. Effect of herbicide treatments on pokeweed control in no-till corn, 2012.

Herbicide

Rate

% Control

% Dry wt. reduction

 

(per/A)

   (8/22)

           (8/22)

Control

--

       0

                0

Roundup Powermax®

32 fl oz

       84

               94

2,4-D

1 pt

       89

               92

Clarity®

1 pt

       86

               87

Status®

10 oz

       88

               96

Callisto® +

3 fl oz

       91

               98

atrazine

1 pt

  

Permit +

0.67 oz

       79

               89

Status®

10 oz

  

Roundup Powermax® +

32 fl oz

       81

               88

Status®

10 oz

  

Roundup Powermax® +

32 fl oz

       82

               87

Callisto® +

3 fl oz

  

atrazine

1 pt

  

Roundup Powermax® +

32 fl oz

       91

               95

Permit® +

0.67 oz

  

Status®

10 oz

  
    

Soybean herbicides

Table 2. Effect of herbicide treatments on pokeweed control in no-till soybean, 2012.

Herbicide

Rate

% Control

% Dry weight reduction (9/4)

Soybean yield

 

(per/A)

   (9/4)

 

    (bu/A)

Control

--

      0

                0

        24

Roundup Powermax®

22 fl oz

      82

                92

        38

Roundup Powermax ®

44 fl oz

      92

                92

        45

Roundup Powermax ® followed by

22 fl oz

      95

                91

        42

Roundup Powermax ®

22 fl oz

   

Classic®

0.75 oz

      33

                49

        29

Harmony®

0.125 oz

      53

                55

        27

Synchrony®

0.375 oz

      48

                72

        41

Synchrony®

1.125 oz

      60

                79

        37

Roundup Powermax ® +

22 fl oz

      91

                88

        42

Synchrony®

0.25 oz

   

Roundup Powermax ® +

22 fl oz

      91

                90

        43

Classic®

0.33 oz

   

Roundup Powermax ® +

22 fl oz

      86

                73

        31

FirstRate®

0.33 oz

   

Roundup Powermax ® +

22 fl oz

      96

                88

        40

Raptor®

5 fl oz

   

The soybean herbicide efficacy study was conducted at the Penn State Rock Springs Research Farm near State College. Eleven POST treatments were evaluated in STS/Roundup Ready® soybeans. (See Table 2.) The pokeweed ranged from one to four feet tall at the time of application. Results show that Roundup® provided 75 to 92% control. The treatments without glyphosate were less effective.

Source : psu.edu


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