Trap Catches to Aug 25 - Sep 01, 2023.
Another week with much lower aphid numbers. With 7 trap locations reporting, we continue to see a steady decrease in both total number of aphids, total number of vectors and average vector capture per trap decreasing. The season is winding down with several trap locations having now vine killed and shutting down traps. The total number of vectors and the regional PVY Vector Risk Index is almost double that of was at this time last year, so it's been a high vector pressure year.
Green peach aphids (GPA) were again recovered in 3 of the 7 sites. English grain aphids are no longer being recovered while soybean aphids, although less numerous are well distributed across the region. Most other vector aphid species have decreased and non-vector species are also down.
While this is good news overall, there are still vectors in the region and as long as vines are green, aphids will be attracted to them. Consequently, green plants means the potential for transmission of virus still exists.
You keep scouting and 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.
Cumulative PVY Vector Risk Index to 9/01/2023
Cumulative PVY Vector Risk Index to 9/02/2022 for Comparison
Weekly Aphid Species Capture and PVY Vector Risk Index for all sites reporting the week ending 9/01/2023
Cumulative Seasonal Aphid Species Capture and PVY Vector Risk Index for all sites to 9/01/2023
