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

Friday, July 8, 2022

Trap Catches to July 08, 2022.

Aphid vector captures increased this week with more traps reporting and numbers at active sites slightly increasing. We are still well behind last year with fewer aphids being recovered in traps than in 2021 (see the maps below for a comparison of this year and July 09 last year). This is understandable given last year's drought played havoc with the fungal diseases that control aphid populations. The spring rains and cooler temperatures this year hopefully allowed those fungi to rebuild and cause some mortality.

Cereal aphids remain low as do soybean aphids. Mostly we have recovered species that are associated with several other crop hosts; cotton melon and buckthorn aphids have been recovered in different locations. The late planting in all cropping systems has probably contributed to the low aphid counts so far. As always, as other crops start to mature, especially small grains, we can probably expect to see some more aphids finding their way into potato fields.

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.