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AUTHOR INFORMATION

Kevin Bradley
University of Missouri
Division of Plant Sciences
206a Waters Hall
Columbia, MO 65211
(573) 882-4039
bradleyke@missouri.edu

Make Sure You Burndown Cover Crops Effectively

Published: March 25, 2014

For those growers who may have planted cover crops last fall, it will be very important to apply an effective burndown to these species in the coming weeks.  Cover crops that aren’t effectively controlled prior to planting this spring can become a weed that takes moisture and nutrients away from the developing corn or soybean plants.  Tables 1-3 show some of our recent research results related to the effects of some common herbicide burndown programs on the control of different cover crop species.

Tables 1 and 2 show the response of wheat, cereal rye, annual ryegrass, crimson clover, hairy vetch, and winter pea to a variety of herbicide burndown treatments.  Table 1 shows the control provided by these treatments when applied earlier in the spring on April 5th, while Table 2 shows the control provided by these same treatments applied later in the spring, on May 1st.  As you can see from the results presented in both tables, it is very important to make a timely and effective burndown herbicide application, regardless of which cover crop species you have present.  Also, it seems clear from our results that the effectiveness of these different herbicide treatments will vary by cover crop species, but overall some of the species that have proven the most difficult to control in our research are annual ryegrass, wheat, and crimson clover.  On the other hand, some of the cover crop species that these burndown treatments have controlled fairly well include cereal rye, hairy vetch, and winter pea.   It is also important to note that tillage radish and oats winter-killed in our experiments, although they were a part of the study initially.  In our experiences so far in central Missouri, neither of these species will over-winter. 

Due to the troublesome and persistent nature of annual ryegrass, we also conducted a separate experiment to evaluate more treatments and timings for the control of this species.  The results from this experiment are shown in Table 3.  Once again, one of the most important take-home messages from this experiment is that the timing of the burndown herbicide application is critical to the level of annual ryegrass control achieved.  For example, in this experiment the average level of annual ryegrass biomass reduction with the glyphosate-containing treatments evaluated was 91% when applications were made to 5 ¾-inch annual ryegrass, but declined to 77 and 58% when these same herbicide treatments were applied to 14- and 36-inch annual ryegrass, respectively. 

There are two other things to keep in mind when it comes to the results of this study.  First, our base rate of Roundup PowerMax that we used in all of these treatments was 36 ounces per acre.  Based on the results from last year’s study it seems clear that this rate may need to be even higher for ryegrass.  Second, we weren’t able to include tank-mixes mixes of glyphosate plus certain grass herbicides like clethodim (SelectMax, Arrow, etc.) in the trial last year but there is some data coming out of the southern United States that shows these mixes are effective.  For example, several weed science colleagues in the southern states where ryegrass problems are more severe have seen good results with glyphosate plus Select Max at 10 to 16 ounces per acre.

Because ryegrass can be especially difficult to control in the spring, consider the following tips to achieve a more effective burndown of this species: 1) make sure to adjust spray settings (higher GPA, nozzle selection, etc.) to optimize spray coverage, 2) spray during daylight hours when annual ryegrass is actively growing, preferably at temperatures around 60 F, 3) spray at least 4 hours prior to sunset to allow for maximum herbicide translocation, and 4) try to avoid spraying when day or night time temperatures are forecasted in the 30’s for an extended period of time.

Table 1. Influence of early spring (April 5th) herbicide treatments
on the control of various cover crop species (Columbia, Missouri 2013)

Herbicide Treatment

Rate

Wheat

Cereal Rye

Annual Ryegrass

Crimson Clover

Hairy Vetch

Cereal Rye/Vetch

Winter Pea

*Avg. Control

 

product/A

% Control 21 Days After Treatment

 

Roundup PowerMax

28 fl ozs

83

98

93

22

20

100

72

70

Roundup PowerMax + 2,4-D

28 fl ozs + 1 pt

65

95

93

33

100

98

78

80

Roundup PowerMax + Clarity

28 fl ozs + 16 fl oz

62

95

88

28

98

98

97

81

Roundup PowerMax + Sharpen

28 fl ozs + 1 fl oz

78

97

92

87

15

95

80

78

Roundup PowerMax + Aatrex

28 fl ozs + 1 qt

32

68

78

38

18

78

70

55

Roundup PowerMax + Canopy

28 fl ozs + 4 ozs

37

63

73

35

15

65

45

48

Gramoxone
Inteon

4 pts

30

57

28

22

20

58

33

35

Gramoxone Inteon + 2,4-D

4 pts + 1 pt

32

57

32

30

95

65

83

56

Gramoxone + Aatrex

4 pts + 1 qt

40

70

78

80

18

75

38

57

LSD0.05:

------------------------------ 15 ------------------------------

 

 

Table 2. Influence of late spring (May 1st) herbicide treatments
on the control of various cover crop species (Columbia, Missouri 2013)

Herbicide Treatment

Rate

Wheat

Cereal Rye

Annual Ryegrass

 Crimson Clover

Hairy Vetch

Cereal Rye/Vetch

Winter Pea

*Avg. Control

 

product/A

% Control 21 Days After Treatment

 

Roundup PowerMax

28 fl ozs

37

93

65

57

97

90

85

75

Roundup PowerMax + 2,4-D

28 fl ozs + 1 pt

30

92

77

58

100

93

85

76

Roundup PowerMax + Clarity

28 fl ozs + 16 fl oz

32

82

67

43

97

82

90

70

Roundup PowerMax + Sharpen

28 fl ozs + 1 fl oz

27

90

75

90

100

78

100

80

Roundup PowerMax + Aatrex

28 fl ozs  + 1 qt

30

33

32

32

98

30

87

49

Roundup PowerMax + Canopy

28 fl ozs + 4 ozs

18

30

22

28

92

23

83

42

Gramoxone
Inteon

4 pts

92

97

95

100

100

100

98

97

Gramoxone Inteon + 2,4-D

4 pts + 1 pt

92

100

95

95

100

98

100

97

Gramoxone + Aatrex

4 pts + 1 qt

95

100

95

82

99

100

100

96

LSD0.05:

------------------------------ 11 ------------------------------

 

 

Table 3. Influence of herbicide treatments and application timings
on the control of an annual ryegrass cover crop (Columbia, Missouri 2013).

 

Application Timing and Ryegrass Stage

Herbicide Treatment

Rate

Early (April 2) 5.75”; Tillering

Mid (April 22) 14”; Pre-boot

Late(May 16) 36”; Boot

 

product/A

% Biomass Reduction 28 Days After Treatment

Roundup PowerMax

36 fl ozs

93

80

63

Roundup PowerMax + 2,4-D

36 fl ozs + 1 pt

92

75

57

Roundup PowerMax + Clarity

36 fl ozs + 1 pt

87

65

64

Roundup PowerMax + Sharpen

36 fl ozs + 1 fl oz

90

76

54

Roundup PowerMax + Aatrex

36 fl ozs  + 1 qt

91

81

55

Roundup PowerMax + Canopy

36 fl ozs + 4 ozs

88

79

47

Roundup PowerMax + Basis Blend

36 fl ozs + 1.25 ozs

83

78

56

Roundup PowerMax

72 fl ozs

90

78

65

Gramoxone Inteon

4 pts

78

77

44

Gramoxone Inteon + 2,4-D

4 pts + 1 pt

90

77

52

Gramoxone Inteon + Aatrex

4 pts + 1 qt

87

82

54

Gromoxone Inteon + Lorox

4 pts + 24 ozs

89

83

50

Gramoxone Inteon + Sencor + 2,4-D

4 pts + 4 ozs + 1 pt

90

87

60

Liberty

29 fl ozs

35

50

34

Liberty + Atrazine

29 fl ozs + 1 qt

71

50

45

LSD0.05  (treatments x timings):

-------------------- 15 ------------------

 

 

 

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