Aphid Alert 2023 - Monitoring PVY Vectors in Minnesota and North Dakota

Friday, September 3, 2021

Trap Catches to August 27, 2021.

Trap capture numbers remained very similar to last week's. The numbers of both vectoring and non-vectoring aphids were almost the same. While trap captures per trap were marginally higher than last week, overall numbers are low. This meant only a small increase in the PVY Vector Risk Index. As mentioned last week, the peak aphid flight obviously occurred early this year and so the risk from PVY vectors is lower than at this time last year (our current regional PVY Vector Risk Index is only ~41% of what it was last year).

The species composition is little changed from last week, Cotton/Melon aphids are down, Soybean aphid numbers are up. Buckthorn and cereal aphids remain relatively the same. Overall, these numbers are promising as the season winds down.

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.