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

Trap Catches July 26 - Aug 02, 2024.

With 14 traps reporting, regional aphid vector numbers are very similar to those of last week and lower this point in 2023. Total number of vectors remained very much the same although there were differences in the species collected. There was one significant difference, the number of trap locations reporting Green Peach Aphid (GPA) has risen and the species was reported from several locations in the region. This may represent recent rain systems coming from the south. Along with similar numbers of aphid vectors, the PVY Vector Risk Index increased by an amount similar to last week. Still, this represents an increase in cumulative seasonal risk.

New locations reporting GPA this week included Becker, Crookston, Forest River and Perham. Lisbon, which has reported GPA already this season, captured 1 again this week as well. So, while the numbers of GPA are low at each location, it's regional distribution may be increasing. It appears the species is now present across most of the trapping area. Soybean aphids were numerous again this week as their late summer dispersal continues. Small grain aphids continue to be numerous as do cotton/melon aphids.

Temperatures are supposed to cool over the next week, but our nighttime lows will remain high enough that we will still be seeing aphid reproduction. While the rate of population development will slow, it will likely not cease. Aphid vector numbers may drop over the next few weeks, but the season is probably far from over. In addition, existing populations remain.

As stated last week, proactive measures, such as the use of crop oils, are recommended through to vine kill. As long as plants are green, they remain attractive to aphids that can vector inoculum. The use of the insecticides Fulfill (active ingredient = pymetrozine) and Beleaf (active ingredient = flonicamid) have been shown to decrease the spread of PVY and also to be beneficial when use in conjunction with crop oils such as Aphoil or JMS Stylet oil.

Bottom line, aphid numbers may (we hope!) drop over the next week, but they're still out there. So... 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).