Aphid Alert 2024 - Monitoring PVY Vectors in Minnesota and North Dakota

Friday, July 14, 2023

Trap Catches to July 7-14, 2023.

With ten traps reporting in, aphid captures remain very low; only 12 vector aphids were captured. We are starting to see the beginning of grain aphid flights. The first soybean aphid was also recovered this week; not surprising given local populations lead us to we believe soybean aphids successfully overwintered in northern Minnesota and North Dakota this year.

The species of vectors that were captured this past week were generally less effective vectors and so the PVY Vector Risk Index remains low. At this point last year capture numbers at several sites were higher and their and PVY Vector Risk values were almost twice what they are now (see below).

Warmer weather is predicted for the upcoming week, so aphid flights might heat up as well. We'll see what the traps capture...

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).