Trap Catches to Sept 02, 2022.
Aphid numbers seemed to have peaked. We recovered far fewer aphids per trap and overall regional numbers are way down this week, resulting in a decrease in the regional PVY Vector Risk Index. It should be noted that this season's cumulative PVY Vector Risk Index remains significantly higher than that of 2021.
(Click on image for larger version)
Green Peach Aphid capture numbers were lower this week, approximately only 60% of last week's numbers. But the species did increase their regional distribution this week, showing up at an additional two locations (Perham and one of the Staples trap locations).
Soybean aphids are also down this week, dropping to almost half of last week, but are also well distributed across the region. As the nights get colder, we should soon see temperatures that will trigger a movement from soybeans to Buckthorn.
There was a drop off in the number of most cereal aphids, with only one English Grain aphid being recovered all week. This is not surprising as cereal crops have matured in most locations and aphid dispersal from those crops will have ended. The only exception was Bird-Cherry Oat aphid, the only species to have an increase in capture numbers this week (although it was only 4 more than last week...) Other than that, all other species were captured at lower numbers.
The season is quickly winding down and many locations are vine killing and harvesting. Hopefully, the aphid numbers will continue to rapidly drop, the weather will stay fine for harvest and the remaining few weeks will go smoothly.
Have a great Labor Day Weekend! 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).
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.
Click on any image below for full-scale version.
Cumulative PVY Vector Risk Index to Sep 02, 2022
Cumulative PVY Vector Risk Index to Sept 03, 2021 (please note different scale)
Aphid Species Capture and PVY Vector Risk Index for the week ending Sep 02, 2022
Cumulative Aphid Species Capture and PVY Vector Risk Index to Sep 02, 2022
