Friday, August 13, 2021


Trap Catches to August 13, 2021.

Aphid vector numbers decreased again this week, although we did see the first Green Peach aphid of the year (but only 1 so far!).  Most species numbers were down over all.

Soybean and Corn Leaf aphids remained roughly the same while English Grain aphids were only half of last week's numbers.  A single Green Peach aphid was recovered from the Ada, MN site.  Numbers of other vector species were also down over all.  Non-vector aphid species decreased by 20% but there are still numerous aphids flying.  

While the season appears to be slowing, remember our peak aphid flights in Minnesota and North Dakota occur through August, explaining why most of our PVY is transmitted later in the season.  There's still a lot of time for aphids to find green plants, so continue appropriate disease management tactics.

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 13, 2021

Cumulative PVY Vector Risk Index to Aug 13, 2020 (for comparison)

Aphid Species Capture and PVY Vector Risk Index for the week ending Aug 13, 2021

Cumulative Aphid Species Capture and PVY Vector Risk Index to Aug 13, 2021