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

Trap Catches Aug 31 - Sept 06, 2024.

With 5 trap locations reporting, the average number of vector aphid species recovered per location has again significantly declined this week, as has the average PVY Vector Risk Index values at each location. The early September drop in aphid numbers agrees closely with the 2012-2023 average of regional aphid population dynamics (see chart).

While numbers are lower, important vector species remain in the trapping area. Both Becker, MN and Crystal ND traps recorded green peach aphids this week. Soybean aphids are lower but still widely distributed (both MN and ND sites reported this species). Other aphid species, including non-vectors, have decreased.

Heavy aphid infestations in central MN commercial fields have continued, becoming wide spread in some fields. Thee higher temperatures this week may continue to drive reproduction somewhat but the cool nights will ameliorate that increase. Many fields have been vine killed and so this is not problematic. For those that are continuing to grow and populations are difficult to control, several aphid-targeted insecticides may be effective; Transform (Cortev; sulfoxaflor), Sivanto Prime (Bayer Cropscience; flupyradifurone), or Sefina (BASF; afidopyropen) are all effective aphicides and have performed well in field trials.

For those locations that have not yet vine killed, virus transmission remains a concern as long as plant material is green and circulating.

Bottom line - aphid populations and PVY Vector Risk significantly decreased again over the last week. 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 Sept 06, 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).