Blue Alfalfa Aphid Issue Summary

May 20, 2013

Of all of the insecticides evaluated against blue alfalfa aphid (BAA) by Eric Natwick of Imperial County, almost every insecticide applied to alfalfa this spring gave initial knockdown of BAA. Blue alfalfa aphid populations resurged in 7-10 days. Treatments giving 70–75% control (reported by PCA’s) were combinations of a pyrethroid with an organophosphate.

Possible factors for our BAA issue:

  • High initial aphid populations
  • Smaller than expected populations of predators and parasites; particularly the seven-spotted lady beetle

                May be weather related or pesticide related

  • Potentially more insecticides to alfalfa than in the past; partially due to cowpea aphid
  • Lack of “bio-rational” for weevil and aphid management in alfalfa
  • Growers are spraying at the time of year when there are the fewest beneficial insects in alfalfa. The insecticides along with cool weather may be preventing or delaying the buildup of beneficial insect populations

 

Blue Alfalfa Aphids per Sweep, Holtville, CA, 2013.

Treatment

fl oz/acre

1 DPTw

3 DATxz

7 DAT

10 DAT

14 DAT

PTAyz

Check

--------

105.05 a

58.58 a

38.83 a

82.50 a

39.10 b

54.75

Warrior II

1.92

127.80 a

10.95 bc

8.63 c

15.55 b

24.23 bc

14.84 b

Endigo ZCX

4.0

84.00 a

1.08 f

3.05 c

4.48 b

13.73 c

5.58 bc

Besiege

9.0

103.05 a

5.55 cd

2.93 c

16.63 b

21.60 bc

11.68 b

Cobalt Advanced

24.0

69.75 a

2.23 de

1.60 c

5.73 b

6.60 c

4.11 c

Mustang

4.3

91.48 a

4.53 d

3.20 c

13.13 b

18.13 bc

9.74 b

Stallion 3.025 EC

9.25

95.98 a

3.53 d

2.38 c

14.33 b

13.45 c

8.42 bc

Stallion 3.025 EC

11.75

105.05 a

2.08 ef

2.25 c

5.48 b

22.45 bc

8.06 bc

Danitol

16.0

115.23 a

13.98 b

22.28 b

65.45 a

65.45 a

41.79 a

 

Blue Alfalfa Aphids per Ten Sweeps, Holtville, CA, 2013.

Treatment

fl oz/acre

PTw

3 DATx

7 DATz

14 DAT

PTAyz

Check

--------

58.48 a

65.66 a

82.64 a

86.36 a

78.22 a

Paradigm VC

3.84

60.02 a

17.12 b

18.68 b

20.16 b

18.65 b

Baythroid XL

1.9

49.58 a

11.84 b

23.20 b

26.12 b

20.39 b

Mustang

4.3

54.44 a

11.42 b

15.40 b

23.00 b

16.61 b

Lorsban Advanced

24.0

81.56 a

8.20 b

7.28 c

15.34 b

10.27 c

Warrior II

1.92

72.64 a

14.58 b

6.94 c

15.92 b

12.48 bc

Means within columns followed by the same letter are not significantly different, LSD; P= 0.05.

w Pre-treatment

x Days after treatment

y Post treatment average

z Log10 (X+1) transformed data used for analysis, ACTUAL MEANS REPORTED


By Vonny M. Barlow
Author - Entomology/IPM /Crop production Advisor
By Eric T. Natwick
Author - Entomology Advisor, emeritus