Trap Catches Identified to September 09, 2019
Aphid captures per location were similar to last week, but fewer locations are reporting with the waning season. A wide variety of species were captured this week, including some efficient vector species. Green Peach Aphid numbers were down to only 3 this week from 2 locations (Crookston and Syre MN). With this week's capture, we are still tracking higher than last season's totals and the PVY Vector Risk Index values.
Ada MN again led aphid captures this week with 76 total vectors being recovered, including Soybean, Corn Leaf, Sunflower, Potato and Cotton/Melon aphids. Crookston and Syre both recovered Green Peach Aphids this week and increases in their PVY Vector Risk Index.
Aphids continue to be entering potato fields in numbers and Oil and early vinekill are recommended practices to decrease late season movement of PVY. Remember: If Potatoes Are Green, By Vectors They'll Be Seen!
Aphid Fact of the Week - The low evening temperatures and decreasing photoperiod will be signalling aphids currently on their summer hosts to develop a winged generation, which will disperse back to overwintering hosts.
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 09, 2019.
Cumulative PVY Vector Risk Index for 2018 (for comparison)
Aphid Species Capture and PVY Vector Risk Index for Aug 30 - Sept. 09, 2019
Cumulative Aphid Species Capture and PVY Vector Risk Index to Sept. 09, 2019