Aphid Alert 1999, No. 11, August 25

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. Data for missing locations (no data) will be incorporated into this week's issue of the newsletter once the samples have been received and sorted.

Figure 1 (below). Mean number of winged green peach aphid captured per trap across all locations reported, 1998 data (blue line) and 1999 data (maroon line). These data are also available in table format (Table 1).

graph showing captures of winged green peach aphids per trap from 1998 and 1999 year to date

Figure 2 (below). Mean number of winged aphids of species known to be capable of transmitting PVY (exclusive of green peach aphid) captured per trap across all locations reported, 1998 data (blue line) and 1999 data (maroon line). These data are also available in table format (Table 1). Summary of observations for week ending 25 August.

graph showing captures of PVY vectors other than green peach aphids per trap from 1998 and 1999 year to date

Green peach aphids per trap declined from 4.30 per trap last week to 3.19 per trap this week. Captures of other potential PVY vectors declined slightly, from 8.82 per trap last week to 8.50 this week.

All winged green peach aphids captured in traps of the Aphid Alert network to date (14 June through 18 August) have tested negative for potato leafroll virus and potato virus Y. Last week, 230 green peach aphids were submitted for testing (Table 1). These results are markedly different from those of last summer, when the first PLRV-positive green peach aphids were collected 14 July. In August of 1998, 59% of the winged green peach aphids captured tested positive for PLRV and in September, 86%. Results of the PCR testing of this weeks captures will be reported here by Wednesday of next week.

The absence of any positives for either PLRV or PVY in the aphids collected this year is consistent with our interpretation that these are migrants moving into the potato crop from hosts other than potato. As indicated in previous updates, we believe canola is the principal source of these winged aphids. Most canola is now mature and much is harvested so that source of green peach aphid is essentially finished. Also, with the recent wet weather, we are seeing a very high level of fungal mycoses (disease) among the remaining green peach aphids on canola. Aphid-infecting fungi are likely to be much less effective in suppressing green peach aphid on potato because of the heavy use of fungicides to control potato late blight.

We are now observing development of winged aphids in potato fields (i.e., the immature stages are developing winged pads). Aphids developing on potatoes are much more likely to acquire and transmit potato viruses. Much current season transmission has already occurred. We believe that to date this has mostly been secondary transmission, i.e., within field transmission from plants grown from infected tubers.

Phil Glogoza, Extension Entomologist at NDSU, has pointed out to us there was relatively little use of insecticides on canola in North Dakota this year. Therefore, our previous suggestion that insecticide use on canola could have contributed to this year's green peach aphid buildup was probably unfounded. Phil observes that the southward expansion of canola production in recent years may simply be providing a very suitable host for green peach aphid arriving from southern overwintering sites (green peach aphid is not known to overwinter outdoors in Minnesota or North Dakota).

We know that many seed potato producers have already killed their potatoes. Unfortunately, many seed lots were planted late this year and early killing will not be a realistic management alternative for these. From this point, routine applications of Monitor or Provado (Admire in Canada) every week or 10 days is probably advisable.

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 23 August

  Aphid species # captured % of total capture
PLRV/PVY vectors green peach aphid 14 43.8
  potato aphid
   
PVY vectors bird cherry-oat aphid 3 9.4
  corn leaf aphid 6 18.8
  English grain aphid 1 3.1
  greenbug
  sunflower aphid 1 3.1
  thistle aphid
  turnip aphid 3 9.4
   
Identified non-vector species   2 6.3
   
Unidentified   2 6.3
   
  Total 32

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Climax, MN, week ending 25 August

  Aphid species # captured % of total capture
PLRV/PVY vectors green peach aphid 13 16.9
  potato aphid
   
PVY vectors bird cherry-oat aphid 4 5.2
  corn leaf aphid 11 14.3
  English grain aphid 2 2.6
  greenbug
  sunflower aphid 7 9.1
  thistle aphid 2 2.6
  turnip aphid 34 44.2
   
Identified non-vector species  
   
Unidentified   4 5.2
   
  Total 77

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Gully, MN, week ending 23 August

  Aphid species # captured % of total capture
PLRV/PVY vectors green peach aphid 5 11.1
  potato aphid
   
PVY vectors bird cherry-oat aphid
  corn leaf aphid 16 35.6
  English grain aphid 1 2.2
  greenbug
  sunflower aphid 19 42.2
  thistle aphid 1 2.2
  turnip aphid 1 2.2
   
Identified non-vector species   2 4.4
   
Unidentified  
   
  Total 45

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Hollandale, MN, week ending 25 August

  Aphid species # captured % of total capture
PLRV/PVY vectors green peach aphid
  potato aphid
   
PVY vectors bird cherry-oat aphid 1 3.1
  corn leaf aphid 18 56.3
  English grain aphid 1 3.1
  greenbug
  sunflower aphid
  thistle aphid 1 3.1
  turnip aphid
   
Identified non-vector species  
   
Unidentified   11 34.4
   
  Total 32

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Karlstad, MN, week ending 25 August

  Aphid species # captured % of total capture
PLRV/PVY vectors green peach aphid 22 56.4
  potato aphid
   
PVY vectors bird cherry-oat aphid 1 2.6
  corn leaf aphid 3 7.7
  English grain aphid 2 5.1
  greenbug
  sunflower aphid 2 5.1
  thistle aphid 1 2.6
  turnip aphid 4 10.3
   
Identified non-vector species   1 2.6
   
Unidentified   3 7.7
   
  Total 39

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Little Falls, MN, week ending 23 August

  Aphid species # captured % of total capture
PLRV/PVY vectors green peach aphid 3 10
  potato aphid
   
PVY vectors bird cherry-oat aphid 2 6.7
  corn leaf aphid 16 53.3
  English grain aphid
  greenbug
  sunflower aphid
  thistle aphid
  turnip aphid 2 6.7
   
Identified non-vector species  
   
Unidentified   7 23.3
   
  Total 30

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Morris, MN, week ending 23 August

  Aphid species # captured % of total capture
PLRV/PVY vectors green peach aphid 9 29
  potato aphid
   
PVY vectors bird cherry-oat aphid
  corn leaf aphid 12 38.7
  English grain aphid
  greenbug
  sunflower aphid
  thistle aphid 1 3.2
  turnip aphid 5 16.1
   
Identified non-vector species  
   
Unidentified   4 12.9
   
  Total 31

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Williams, MN, week ending 23 August

  Aphid species # captured % of total capture
PLRV/PVY vectors green peach aphid
  potato aphid 1 2.2
   
PVY vectors bird cherry-oat aphid 6 13.3
  corn leaf aphid 18 40
  English grain aphid 2 4.4
  greenbug 1 2.2
  sunflower aphid 2 4.4
  thistle aphid
  turnip aphid 2 4.4
   
Identified non-vector species   7 15.5
   
Unidentified   6 13.3
   
  Total 45

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Cando, ND, week ending 20 August

  Aphid species # captured % of total capture
PLRV/PVY vectors green peach aphid 2 22.2
  potato aphid
   
PVY vectors bird cherry-oat aphid 1 11.1
  corn leaf aphid 3 33.3
  English grain aphid
  greenbug
  sunflower aphid 1 11.1
  thistle aphid
  turnip aphid 2 22.2
   
Identified non-vector species  
   
Unidentified  
   
  Total 9

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Hoople, ND, week ending 20 August

  Aphid species # captured * % of total capture
PLRV/PVY vectors green peach aphid 65 (71) 46.1
  potato aphid 4 (4) 2.8
   
PVY vectors bird cherry-oat aphid 4 (4) 2.8
  corn leaf aphid 1 (1) 0.7
  English grain aphid 2 (2) 1.4
  greenbug
  sunflower aphid 3 (3) 2.1
  thistle aphid 4 (4) 2.8
  turnip aphid 54 (59) 38.3
   
Identified non-vector species   1 (1) 0.7
   
Unidentified   3 (3) 2.1
   
  Total 141/155

*Actual numbers in sorted subsample (projected numbers in total collection)

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Linton, ND, week ending 23 August

  Aphid species # captured % of total capture
PLRV/PVY vectors green peach aphid 6 9.2
  potato aphid
   
PVY vectors bird cherry-oat aphid
  corn leaf aphid 2 3.1
  English grain aphid 1 1.5
  greenbug
  sunflower aphid 2 3.1
  thistle aphid
  turnip aphid 53 81.5
   
Identified non-vector species  
   
Unidentified   1 1.5
   
  Total 65

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Mandan, ND, week ending 23 August

  Aphid species # captured * % of total capture
PLRV/PVY vectors green peach aphid 19 61.3
  potato aphid
                
PVY vectors bird cherry-oat aphid 1 3.2
  corn leaf aphid 2 6.5
  English grain aphid 1 3.2
  greenbug   
  sunflower aphid 1 3.2
  thistle aphid 2 6.5
  turnip aphid 5 16.1
               
Identified non-vector species  
         
Unidentified  
         
  Total 31   

*Actual numbers in sorted subsample (projected numbers in total collection)

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Rolette, week ending 20 August

  Aphid species # captured * % of total capture
PLRV/PVY vectors green peach aphid 7 (16) 9.3
  potato aphid
                
PVY vectors bird cherry-oat aphid
  corn leaf aphid         
  English grain aphid 1 (2) 1.3
  greenbug   
  sunflower aphid 8 (18) 10.7
  thistle aphid
  turnip aphid 55 (123) 73.3
               
Identified non-vector species   2 (4) 2.7
         
Unidentified   2 (4) 2.7
         
  Total 75/168   

*Actual numbers in sorted subsample (projected numbers in total collection)

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Walhalla, ND, week ending 20 August

  Aphid species # captured % of total capture
PLRV/PVY vectors green peach aphid 43 30.1
  potato aphid 2 1.4
        
PVY vectors bird cherry-oat aphid 2 1.4
  corn leaf aphid 8 5.6
  English grain aphid 3 2.1
  greenbug             
  sunflower aphid 2 1.4
  thistle aphid 5 3.5
  turnip aphid 61 42.7
         
Identified non-vector species   3 2.1
             
Unidentified   14 9.8
             
  Total 143

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