Trap Catches Identified to August 24th
The downward trend continues, with even fewer aphids this week than last!
This week we recovered a total of 133 aphids, 117 of which were vectors. We did, however, only have 10 sites reporting. Of those sites, we saw the heaviest flights from Sabin (36) and Staples (21). Soybean Aphid was moving last week, with 25 being captured between Crookston, Staples, Sabin and Ballard. If you have soybeans still in a susceptible growth stage (younger than R6), keep your eyes open. There was some good news for the trapping area - no Green Peach this week! However, Dr. Gloom (Dr. Neil Gudmestad) mentioned to us yesterday that there have been reports of Green Peach aphid in southern Minnesota and South Dakota. We don't have any traps down in southern MN so we sadly don't have data - may need to install a couple of traps down there next year...
Just because the year is winding down a bit, that doesn't mean that aphids are completely done wreaking havoc. Aphids will be active well into September, so unless you've vine-killed - you should still be 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).
Cumulative PVY Vector Risk Index Map to August 24th, 2018
Cumulative PVY Vector Risk Index Map for 2017
(included for comparison)
Aphid Species Capture + PVY Risk - Week of August 19th, 2018
Total PVY Risk and Species Capture to August 24th, 2018