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

Wednesday, July 7, 2021

Trap Catches to July 02, 2021.

There have been high numbers of aphids in some traps this week, but the number of aphids that vector PVY remains relatively low (although a little ahead of last year but much lower than 2019). The vast number of aphids recovered in traps up to July 02 have been non-vector species. Consequently, the PVY Vector Risk Index values remain low to this point as well.

The weather conditions still favor aphid population development and small grains are starting to senesce early. Several locations have reported late season aphids on wheat, as the grain dries, these populations will generate a winged generations that will disperse to the remaining green crops, like potatoes. All of this means aphid populations will continue to rise.

We'll keep reporting numbers. As always, keep on scouting!

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.