Friday, August 20, 2021


Trap Catches to August 20, 2021.

The numbers of aphid vector species decreased significantly this week.  The number of trap locations reporting decreased by 25%, but the number of vectors recovered decreased by 75%.    

The numbers of all vector species but Buckthorn aphids decreased this week, as did the number of non-vector  species.  The lower number of vectors resulted in only a small increase in the PVY Vector Risk Index.  

Our aphid population dynamics are very different from last year.  In 2020, a late season increase in vector numbers drove the PVY Risk higher.  It seems this year we are seeing an early decrease in vector numbers.  Compare the graphs below.  The first is the 12 regional year average weekly vector capture.  The second is the regional weekly vector capture to this point in 2021.  It remains to be seen if the pattern continues, but the high temperatures and drought this season may have driven both plant host and aphid populations along faster than in previous years.  Just a guess at this point...

Harvest is coming but the later varieties in areas that caught some moisture may still have a lot of green out there.  And that's just the color being sought by any vector still flying out there.

If It's Green, Then By Aphids It Can Be Seen!  

Yes, I know, that one's coming back to haunt me....  

 Keep scouting, 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).

Click on any image below for full-scale version.

Cumulative PVY Vector Risk Index to Aug 20, 2021

Cumulative PVY Vector Risk Index to Aug 21, 2020 (please note different scale) 

Aphid Species Capture and PVY Vector Risk Index for the week ending Aug 20, 2021

Cumulative Aphid Species Capture and PVY Vector Risk Index to Aug 20, 2021