Aphid Alert 1999, No. 10, August 18

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 18 August.

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

Captures of winged green peach aphid averaged 4.3 per trap at 12 locations during the week ending 18 August. Data from two sites, Linton, ND and Mandan, ND are not yet available. This is the highest rate of green peach aphid capture that we have experienced in the 5 years that we have operated traps in the Red River Valley, 1991-1993, and 1998-1999.

We are quite certain that most of the green peach aphids and the turnip aphids (the aphid species that has been the most abundant in our traps this summer) are coming from canola. Aphid numbers in canola fields are often extremely high. It may be that the insecticides used on canola have contributed to this problem by eliminating aphid natural enemies.

In seed potato fields, we have observed a very strong "edge effect" associated with this "invasion" of winged green peach aphids, i.e., we find greatest numbers of winged aphids on the outside rows (e.g., the first 20 meters) and few winged aphids on the interior of potato fields. As time progresses, we expect these invaders to disperse across the field depositing their progeny.

All the winged green peach aphids captured in traps of the Aphid Alert network are sent to Dr. Ben Lockhart, Department of Plant Pathology, to assay by PCR for the presence of leafroll (PLRV) and mosaic (PVY). To date (data available only for captures through 8 August), all have tested negative for both viruses. However, some current season infection has been observed by state seed potato inspectors. Most of the current season infection of PVY and PLRV observed in seed fields has been in the first 6-7 rows. Spraying the margins of potato fields with Monitor or Provado (Admire in Canada) to kill newly arrived winged green peach aphids and prevent establishment of their progeny could be effective at this time.

Many of the seed potato fields we have visited are decidely late in tuber-bulking. For growers in this situation, early vine-kill will not be an option. It may be advisable to harvest and treat the outside rows as a separate seed lot.

If you are monitoring your crop for aphids, keep in mind that aphid flight mostly occurs on warm, sunny days when wind speeds are very low (e.g., 1-2 mph). Therefore, not surprisingly, aphid flight activity is most likely in early morning or late afternoon. When the weather is cold, windy, or wet, expect little aphid flight activity. By timing your sampling to coincide with circumstances favorable for flight you will have the best chance of detecting invasion before the aphids have dispersed in your field.

Captures of other aphid species known to be potential vectors of PVY have declined for the second consective week. Numbers are now far lower (<4%) than on the same date last year. There have been few "cereal aphids" captured this year other than bird cherry-oat aphid. With the cereals ripening there are now few cereal aphids flying. This year, the most abundant, non-potato colonizing, potential vectors of PVY have been turnip aphid, suflower aphid and corn leaf aphid.

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 16 August

  Aphid species # captured % of total capture
PLRV/PVY vectors green peach aphid 5 38.5
  potato aphid
   
PVY vectors bird cherry-oat aphid
  corn leaf aphid 3 23.1
  English grain aphid
  greenbug
  sunflower aphid
  thistle aphid 1 7.7
  turnip aphid
   
Identified non-vector species   3 23.1
   
Unidentified   1 7.7
   
  Total 13

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Climax, MN, week ending 16 August

  Aphid species # captured % of total capture
PLRV/PVY vectors green peach aphid 15 14.7
  potato aphid
   
PVY vectors bird cherry-oat aphid
  corn leaf aphid 5 4.9
  English grain aphid
  greenbug
  sunflower aphid 1 1
  thistle aphid
  turnip aphid 78 76.5
   
Identified non-vector species  
   
Unidentified   3 2.9
   
  Total 102

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Gully, MN, week ending 16 August

  Aphid species # captured % of total capture
PLRV/PVY vectors green peach aphid 2 2.2
  potato aphid
   
PVY vectors bird cherry-oat aphid 17 18.7
  corn leaf aphid 1 1.1
  English grain aphid
  greenbug
  sunflower aphid 23 25.3
  thistle aphid
  turnip aphid 38 41.8
   
Identified non-vector species   3 3.3
   
Unidentified   7 7.7
   
  Total 91

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Hollandale, MN, week ending 18 August

  Aphid species # captured % of total capture
PLRV/PVY vectors green peach aphid 1 2.5
  potato aphid
   
PVY vectors bird cherry-oat aphid 1 2.5
  corn leaf aphid 22 55
  English grain aphid
  greenbug
  sunflower aphid 3 7.5
  thistle aphid
  turnip aphid 1 2.5
   
Identified non-vector species   3 7.5
   
Unidentified   9 22.5
   
  Total 40

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Karlstad, MN, week ending 18 August

  Aphid species # captured % of total capture
PLRV/PVY vectors green peach aphid 20 19.6
  potato aphid 1 1
   
PVY vectors bird cherry-oat aphid 3 2.9
  corn leaf aphid 3 2.9
  English grain aphid
  greenbug
  sunflower aphid 32 31.4
  thistle aphid 1 1
  turnip aphid 33 32.4
   
Identified non-vector species   4 3.9
   
Unidentified   5 4.9
   
  Total 102

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Little Falls, MN, week ending 17 August

  Aphid species # captured % of total capture
PLRV/PVY vectors green peach aphid 2 6.1
  potato aphid
   
PVY vectors bird cherry-oat aphid 2 6.1
  corn leaf aphid 11 33.3
  English grain aphid 1 3
  greenbug
  sunflower aphid 4 12.1
  thistle aphid 1 3
  turnip aphid 8 24.2
   
Identified non-vector species  
   
Unidentified   4 12.1
   
  Total 33

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Morris, MN, week ending 16 August

  Aphid species # captured % of total capture
PLRV/PVY vectors green peach aphid 8 38.1
  potato aphid
   
PVY vectors bird cherry-oat aphid
  corn leaf aphid 8 38.1
  English grain aphid
  greenbug
  sunflower aphid
  thistle aphid 3 14.3
  turnip aphid 2 9.5
   
Identified non-vector species  
   
Unidentified  
   
  Total 21

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Williams, MN, week ending 16 August

  Aphid species # captured % of total capture
PLRV/PVY vectors green peach aphid 5 13.2
  potato aphid
   
PVY vectors bird cherry-oat aphid 5 13.2
  corn leaf aphid 16 42.1
  English grain aphid 1 2.6
  greenbug
  sunflower aphid 1 2.6
  thistle aphid 1 2.6
  turnip aphid 3 7.9
   
Identified non-vector species   4 10.5
   
Unidentified   2 5.3
   
  Total 38

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Cando, ND, week ending 13 August

  Aphid species # captured % of total capture
PLRV/PVY vectors green peach aphid 15 35.7
  potato aphid
   
PVY vectors bird cherry-oat aphid 4 9.5
  corn leaf aphid
  English grain aphid 2 4.8
  greenbug
  sunflower aphid
  thistle aphid 4 9.5
  turnip aphid 11 26.2
   
Identified non-vector species  
   
Unidentified   6 14.3
   
  Total 42

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Hoople, ND, week ending 13 August

  Aphid species # captured * % of total capture
PLRV/PVY vectors green peach aphid 85 (114) 58.2
  potato aphid 10 (13) 6.8
   
PVY vectors bird cherry-oat aphid 1 (1) 0.7
  corn leaf aphid 6 (8) 4.1
  English grain aphid 2 (3) 1.4
  greenbug
  sunflower aphid 7 (9) 4.8
  thistle aphid 6 (8) 4.1
  turnip aphid 19 (25) 13
   
Identified non-vector species   1 (1) 0.7
   
Unidentified   9 (12) 6.2
   
  Total 146/195

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

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Linton, ND, week ending 15 August

Data not available

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Mandan, ND, week ending 15 August

Data not available

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Rolette, week ending 13 August

  Aphid species # captured % of total capture
PLRV/PVY vectors green peach aphid 10 20
  potato aphid
                
PVY vectors bird cherry-oat aphid 2 4
  corn leaf aphid         
  English grain aphid 1 2
  greenbug   
  sunflower aphid 2 4
  thistle aphid 2 4
  turnip aphid 32 64
               
Identified non-vector species   1 2
         
Unidentified  
         
  Total 50   

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Walhalla, ND, week ending 13 August

  Aphid species # captured % of total capture
PLRV/PVY vectors green peach aphid 51 33.1
  potato aphid 2 1.3
        
PVY vectors bird cherry-oat aphid 1 0.6
  corn leaf aphid 3 1.3
  English grain aphid 4 2.6
  greenbug             
  sunflower aphid 2 1.3
  thistle aphid 11 7.1
  turnip aphid 61 39.6
         
Identified non-vector species   4 2.6
             
Unidentified   15 9.7
             
  Total 154

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