Aphid Alert 1999, No. 5, July 13

Summer 1999: Aphid trapping data

Results reported in this issue of Aphid Alert are total captures of winged aphids and species identifications for the following locations and sampling interval end-dates. Missing locations will be incorporated in this issue of the newsletter when available.

Discussion of results through week ending 13 July

Aphid numbers are increasing rapidly. Mean numbers of winged aphids captured in traps of the aphid surveillance network have been consistently higher than on the same dates last year. While numbers are still much lower than the peak densities that occurred in 1998, the trends portend a potentially serious situation. As of this date, aphid populations are at levels not reached until 1-2 weeks later in the year in 1998. Green peach aphids have been caught consistently in the traps the past two weeks. None of the green peach aphids captured prior to this past week have tested positive for mosaic (PVY) or potato leafroll virus (PLRV). Results from the testing of this week's green peach aphid captures will be reported early next week.

The great unknown in aphid trapping is whether the traps (pan or suction) measure anything more than local (within field) movement of winged aphids. We suspect they may not. Monitoring aphid flight will be most useful in terms of "virus management" if the captures actually do represent long distance (inter-field) dispersal. There are no established economic thresholds for vector numbers that we can reference for management decisions. Experience last year showed that green peach aphid captured before mid-Jul were usually not carrying virus. After mid-Jul, the proportion of green peach aphids carrying virus was considerably higher. We suspect that when total aphid captures approach 50 per trap or 1 green peach aphid per trap, the risk of virus spread is high. Obviously, aphid numbers are only part of this equation; the proportion of the aphid population that is capable of transmitting virus and the duration of the crop's exposure are also key elements.

Relatively high numbers of aphids are being found colonizing this year's potato crop. Most often, these are green peach aphid. The accepted threshold for wingless green peach aphid in seed potatoes is 3-10 per 100 leaves. In table stock, the threshold is 10X higher except in cultivars susceptible to "net necrosis." It is important to maintain control when population densities are still low, because it is virtually impossible to reestablish control after the population reaches outbreak levels.

This year, green peach aphid has also been found in relatively high numbers on a wide range of weed and crop hosts including canola, sugarbeet, redroot pigweed and lambs quarters. Aphids moving to potato from these sources are unlikely to be carrying virus. Green peach aphids moving from fields with a high incidence of potato viruses are very likely to be carrying virus. Turnip aphid numbers are generally declining. We believe these are coming to potato from canola.

We maintain a list of e-mail addresses to facilitate communication with those of you interested in receiving updates about this research or any resulting advisories sooner than this information can be delivered by mail or even before it is posted on the WWW. If you wish your name added to receive such messages please send us an e-mail at radcl001@umn.edu. In the message, write "Aphid Alert subscribe."

Errors: If you find errors, typographic or factual, we would appreciate having them called to our attention so they can be corrected. Phone: Robert Suranyi (218) 773-3346 or Ted Radcliffe (612) 624-773 or send an e-mail to radcl001@umn.edu.

 

Results

Minnesota: Baker, Climax, Gully, Hollandale, Karlstad, Little Falls, Morris, Williams
North Dakota: Cando, Hoople, Linton, Mandan, Rolette, Walhalla

Baker, MN, week ending 13 July

  Aphid species # captured % of total capture
PLRV/PVY vectors green peach aphid 3 3.8
  potato aphid 4 5.8
       
PVY vectors bird cherry-oat aphid 6 6.3
  corn leaf aphid    
  English grain aphid 3 3.8
  greenbug    
  sunflower aphid 10 12.7
  thistle aphid 8 10.1
  turnip aphid 11 13.9
       
Identified non-vector species   16 19
       
Unidentified   18 22.8
  Total 79  

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Climax, MN, week ending 13 July

  Aphid species # captured % of total capture
PLRV/PVY vectors green peach aphid 5 11.1
  potato aphid    
       
PVY vectors bird cherry-oat aphid 8 17.8
  corn leaf aphid    
  English grain aphid 3 6.7
  greenbug    
  sunflower aphid 1 2.2
  thistle aphid 4 8.9
  turnip aphid 4 8.9
       
Identified non-vector species   10 22.2
       
Unidentified   10 22.2
  Total 45  

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Gully, MN, week ending 13 July

  Aphid species # captured % of total capture
PLRV/PVY vectors green peach aphid 1 3.1
  potato aphid 1 3.1
       
PVY vectors bird cherry-oat aphid 11 34.4
  corn leaf aphid 1 3.1
  English grain aphid 3 9.4
  greenbug    
  sunflower aphid    
  thistle aphid 4 12.5
  turnip aphid    
       
Identified non-vector species   6 18.8
       
Unidentified   5 15.6
  Total 32  

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Hollandale, MN, week ending 15 July

Data not available

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Karlstad, MN, week ending 15 July

  Aphid species # captured % of total capture
PLRV/PVY vectors green peach aphid 1 3.1
  potato aphid 4 12.5
       
PVY vectors bird cherry-oat aphid 12 37.5
  corn leaf aphid    
  English grain aphid 1 3.1
  greenbug    
  sunflower aphid    
  thistle aphid 2 6.3
  turnip aphid 3 9.4
       
Identified non-vector species   4 12.5
       
Unidentified   5 15.6
  Total 32  

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Little Falls, MN, week ending 11 July

  Aphid species # captured % of total capture
PLRV/PVY vectors green peach aphid    
  potato aphid 6 18.8
       
PVY vectors bird cherry-oat aphid 15 46.9
  corn leaf aphid    
  English grain aphid 1 3.1
  greenbug    
  sunflower aphid    
  thistle aphid 3 9.4
  turnip aphid 2 6.3
       
Identified non-vector species   1 3.1
       
Unidentified   4 12.5
  Total 32  

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Morris, MN, week ending 12 July

  Aphid species # captured % of total capture
PLRV/PVY vectors green peach aphid 15 16.1
  potato aphid 2 2.2
       
PVY vectors bird cherry-oat aphid 2 2.2
  corn leaf aphid    
  English grain aphid 1 1.1
  greenbug    
  sunflower aphid    
  thistle aphid 46 49.5
  turnip aphid 4 4.3
  other vectors 1 1.1
       
Identified non-vector species   13 14
       
Unidentified   10 10.8
  Total 93  

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Williams, MN, week ending 13 July

  Aphid species # captured % of total capture
PLRV/PVY vectors green peach aphid    
  potato aphid 1 5
       
PVY vectors bird cherry-oat aphid 1 5
  corn leaf aphid    
  English grain aphid    
  greenbug    
  sunflower aphid    
  thistle aphid 9 45
  turnip aphid 1 5
       
Identified non-vector species   4 20
       
Unidentified   4 20
  Total 20  

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Cando, ND, week ending 9 July

  Aphid species # captured % of total capture
PLRV/PVY vectors green peach aphid    
  potato aphid    
       
PVY vectors bird cherry-oat aphid 3 30
  corn leaf aphid    
  English grain aphid 1 10
  greenbug    
  sunflower aphid    
  thistle aphid    
  turnip aphid 2 20
       
Identified non-vector species   1 10
       
Unidentified   3 30
  Total 10  

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Hoople, ND, week ending 9 July

  Aphid species # captured % of total capture
PLRV/PVY vectors green peach aphid 1 5.3
  potato aphid 1 5.3
       
PVY vectors bird cherry-oat aphid 9 47.4
  corn leaf aphid    
  English grain aphid    
  greenbug    
  sunflower aphid 1 5.3
  thistle aphid 2 10.5
  turnip aphid    
  other vectors 1 5.3
       
Identified non-vector species   3 15.8
       
Unidentified   1 5.3
  Total 19  

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Linton, ND, week ending 11 July

  Aphid species # captured % of total capture
PLRV/PVY vectors green peach aphid 6 4.1
  potato aphid 7 12.2
       
PVY vectors bird cherry-oat aphid 2 4.1
  corn leaf aphid    
  English grain aphid    
  greenbug    
  sunflower aphid 1 2
  thistle aphid 1 2
  turnip aphid 26 53.1
       
Identified non-vector species   3 6.1
       
Unidentified   3 6.1
  Total 49  

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Mandan, ND, week ending 11 July

  Aphid species # captured % of total capture
PLRV/PVY vectors green peach aphid 1 1.4
  potato aphid 7 9.9
       
PVY vectors bird cherry-oat aphid 7 9.9
  corn leaf aphid    
  English grain aphid    
  greenbug    
  sunflower aphid 1 1.4
  thistle aphid 4 6.6
  turnip aphid 41 57.8
       
Identified non-vector species   5 7
       
Unidentified   5 7
  Total 71  

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Rolette, week ending 9 July

  Aphid species # captured % of total capture
PLRV/PVY vectors green peach aphid    
  potato aphid 1 7.7
       
PVY vectors bird cherry-oat aphid 1 7.7
  corn leaf aphid    
  English grain aphid    
  greenbug    
  sunflower aphid 9 69.2
  thistle aphid    
  turnip aphid    
       
Identified non-vector species   1 7.7
       
Unidentified   1 7.7
  Total 13  

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Walhalla, ND, week ending 8 July

  Aphid species # captured % of total capture
PLRV/PVY vectors green peach aphid    
  potato aphid 1 16.7
       
PVY vectors bird cherry-oat aphid 2 33.3
  corn leaf aphid    
  English grain aphid    
  greenbug    
  sunflower aphid    
  thistle aphid    
  turnip aphid    
       
Identified non-vector species   1 16.7
       
Unidentified   2 33.3
  Total 6  

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