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

Trap Catches Aug 16 - Aug 23, 2024.

With 9 trap locations reporting this week, the average number of vector aphid species recovered per location is slightly down from last week, but the change in species resulted in a similar level of PVY Vector Risk Index. Our numbers and PVY Vector Risk remain very close to the 2012-2023 average (see the chart below (see chart). The 12 year average of aphid vector populations in MN & ND indicates decreasing numbers through the end of August, but presence persists into September.

The only aphid species with a significant drop this week was soybean aphids. Most other vector species numbers were down slightly from last week with the exception of buckthorn, black bean, and potato aphids. The relative efficacies of soybean and the increasing species resulted in there being little change in the average PVY Vector Risk index from Aug 16 to Aug 23.

Some locations have already vine killed, but for those that have not, remember the adage - If leaves are green, by aphids they're seen! Yeah, corny, but true. As long as plant material is green and circulating, the plant is still susceptible to feeding by aphids and potential virus transmission.

Bottom line - aphid populations slightly decreased but the vector risk remained the same as last week. Meaning any field that is not yet vine killed remains susceptible to potential virus transmission...

The top chart shows the average regional aphid vector captures/trap and PVY Vector Risk Index to Aug 23, 2024. The lower graph shows the regional average aphid vector captures/trap and PVY Vector Risk Index averaged from 2012 to 2023. The dates are expressed in ISO Week numbers (a standardized method of presenting dates across years).

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).