Trap Catches to Aug 05, 2022.

Aphid vector numbers continued to rise this week, putting us into a later growing population than last year.  By this time in 2021, aphid captures had already peaked and were decreasing while this year's populations are still growing (see graphs below).  Last year's level of both aphid capture and PVY Vector Risk at this time of the season were much higher, mostly because of the number of English Grain Aphids which were numerous at all trapping locations in 2021.  The temperatures drought of 2021 drove aphid numbers high early in the summer.  This year, more moderate temperatures and more frequent rain have both moderated aphid population dynamics while providing better late season conditions for aphid populations in the area.  

(Click on image for larger version)

The species composition of the aphid captures are different this year, with no individual species dominating the catch to the extent that English Grain Aphid did last year.  That being said, Thistle Aphid was common this week and has become the most numerous vector captured this year and the only one to be recovered at all trapping locations.  Soybean Aphids are starting to increase and are being recovered from more trap locations.  This is not surprising for this time of year, Bruce Potter in Lamberton reported today that the southern migration has started this week.  We can probably expect more Soybean Aphids in our traps next week.  Cereal aphid numbers continue to rise, with the later maturing grain crop this year, these species also may well increase next week.  We also recovered our first Green Peach Aphid since 2020 this week.  Green Peach Aphid is, of course, the most effective vector of PVY.  Only a single Green Peach Aphid was recovered, lets hope she's lonely!   

So... Keep scouting, and we'll keep counting...

Scouting for aphids in potatoes:

- Select leaves from the lower to mid canopy. Start at the edge of the field.

- Lower, older leaves will have more established colonies and aphids prefer the balance of nutrients found here; aphids are rarely found on leaves in the upper canopy.

- Avoid leaves on the ground or in contact with the soil.

- In seed potatoes there is only a threshold for PLRV (10 aphids/100 leaves), reactive application of insecticides an effective control for PVY.

- The use of feeding suppressing insecticides, such as pymetrozine (Fulfill®) or flonicamid (Beleaf®) and refined crop oils, such as Aphoil and JMS Stylet Oil, at or prior to field colonization by aphids may reduce the transmission of PVY within fields. Some other insecticides, such as clothianidin (Belay®), imidacloprid (Admire Pro® or Provado®), and spirotetramat (Movento®), have also been demonstrated to reduce the transmission of PVY.

- In table stock potatoes, a treatment threshold of 30 aphids /100 leaves should deter yield loss due to aphid feeding.

The PVY Risk Index Index

Not all species of aphid are equally efficient at transmitting PVY, some are better than others (green peach being the most efficient vector of PVY).  So, the total number of aphids in a trap don't necessarily reflect just how much vector pressure there is at that location.  The PVY Vector Risk Index compares aphid numbers, incorporating their relative vector efficiency compared to the Queen of PVY vectors (green peach aphid!).  Using averaged reference comparisons from the literature, we multiply the number of each aphid species captured by its efficiency compared to Green Peach Aphid to more accurately depict risk posed by the species being trapped.  We then sum the totals.  The PVY-VRI values are presented on the tables below but also on maps comparing current cumulative risk to the total risk from the sample sites of last year (to compare with your local winter grow out results).

Scouting for aphids in potatoes:

- Select leaves from the lower to mid canopy. Start at the edge of the field.

- Lower, older leaves will have more established colonies and aphids prefer the balance of nutrients found here; aphids are rarely found on leaves in the upper canopy.

- Avoid leaves on the ground or in contact with the soil.

- In seed potatoes there is only a threshold for PLRV (10 aphids/100 leaves), reactive application of insecticides an effective control for PVY.

- The use of feeding suppressing insecticides, such as pymetrozine (Fulfill®) or flonicamid (Beleaf®) and refined crop oils, such as Aphoil and JMS Stylet Oil, at or prior to field colonization by aphids may reduce the transmission of PVY within fields. Some other insecticides, such as clothianidin (Belay®), imidacloprid (Admire Pro® or Provado®), and spirotetramat (Movento®), have also been demonstrated to reduce the transmission of PVY.

- In table stock potatoes, a treatment threshold of 30 aphids /100 leaves should deter yield loss due to aphid feeding.

Click on any image below for full-scale version.

Cumulative PVY Vector Risk Index to Aug. 05, 2022

Cumulative PVY Vector Risk Index to Aug 06, 2021 (please note different scale) 

Aphid Species Capture and PVY Vector Risk Index for the week ending Aug 05, 2022

Cumulative Aphid Species Capture and PVY Vector Risk Index to Aug 05, 2022