Friday, July 28, 2023


Trap Catches to July 21-28, 2023.

What a difference a week makes, aphid numbers are way up...  Higher temperatures have driven aphid population development and is likely responsible for the increase in aphid flights we recorded for the last trapping period.  With 14 traps in MN and ND reporting, we had a total of 550 vector aphids captured in traps.  There were also high numbers of non-vector aphids recovered.  

We had the return of a single green peach aphids from Becker, MN.  The seasonal late season dispersal flights of soybean aphids has started with a total of 115 aphids from 12 of the 14 traps reporting.  English grain aphids, prominent in our small grains this season, are moving from small grains in search of alternate hosts as grain continues to mature; we recovered an overall total of 124 individuals with every site but two (Perham and Staples I) returning varying numbers.  The numbers and distribution of potato and thistle aphids were both up and cotton/melon aphids were also numerous and widespread. 

Along with the increased numbers, the PVY Vector Risk across the region rose, but wasn't consistent across all trap sites.  Compared to this time last year, both 2022 total aphids and vector species captured were about half of 2023 numbers.  Overall, this season's aphid captures seems slightly higher than the 2012-2020 average but still has roughly the same pattern of growth.  But, remembering last year's rapid late season increase in aphids, it's still too early to say what the rest of the season has in store...

So, you 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 7/28/2023

Cumulative PVY Vector Risk Index to 7/29/2022 for Comparison

Aphid Species Capture and PVY Vector Risk Index for the week ending 7/28/2023

Cumulative Aphid Species Capture and PVY Vector Risk Index to 7/28/2023