Trap Catches to Aug 26, 2022.

Another big week for aphid captures.  A total of 418 aphids were captured across all locations this week (350 of which were vectors of PVY), compared to only 316 last week (of which only 290 were vectors).  So our aphid numbers rose again this week.  Typically, our aphid numbers start to decrease by the last week in August.  It will be interesting to see what happens next week.

(Click on image for larger version)

A large number of Green Peach Aphids were recovered again this week resulting in a big rise in the Regional PVY Vector Risk Index.  Soybean Aphids continue to be active and were recovered at multiple locations.  Both Corn Leaf and English Grain Aphids continue to be numerous as do Thistle Aphids and Cotton/Melon Aphids.  Cannabis aphid captures have also increased this week.  

For the first time this year, the number of vector species aphids have surpassed that of 2021 and our PVY Vector Risk Index is more than twice that of this time last year.  The late season increase of aphids capable of vectoring PVY has made this a high risk year.  

Several locations in MN and ND have already been able to start vine kill.  But if there's still green material in the field, PVY can still be vectored by aphids.  So, given the number of vector populations present, appropriate management should be considered.   

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).

Click on any image below for full-scale version.

Cumulative PVY Vector Risk Index to Aug. 26, 2022

Cumulative PVY Vector Risk Index to Aug 27, 2021 (please note different scale)

Aphid Species Capture and PVY Vector Risk Index for the week ending Aug 26, 2022

Cumulative Aphid Species Capture and PVY Vector Risk Index to Aug 26, 2022