Trap Catches Identified to September 11, 2020.
Aphid vector captures were down at all locations this week; the cooler temperatures slowing down reproduction and movement. There were a total of 63 individual aphids from 11 different species as compared to 172 aphids from 16 vector species last week. Still, there does seem to be several species well represented in the area.
Green peach aphids are still present, 7 being recovered from 4 locations (Humboldt, Sabin and Perham all reported GPA). Soybean aphid numbers are lower this week, as are numbers of small grain aphids. Thistle aphids have decreased but are still present, and buckthorn aphid numbers remain steady as they migrate back to their overwintering host.
Overall, this is an expected week, with the season winding down, many fields already vine-killed and harvest underway. We hope all's going well for everyone in the field.
As today is 9/11, lets also take a moment to remember those brave individuals who run towards danger in order to safeguard us all.
As always, 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).
Click on any image below for full-scale version.
Cumulative PVY Vector Risk Index to September 11, 2020.
Cumulative PVY Vector Risk Index to September 09, 2019 season (for comparison)