Trap Catches Identified to August 21, 2020.
We had another big week for aphid vector numbers, with very similar numbers to last week. A total of 287 vectors were recovered from 15 sites reporting. In fact, with this week's catch, we've caught up with 2019 and are pretty much at the same levels, but with different levels at different sites....
A number of efficient vector species were recovered from most locations. Green peach aphids were found in Sabin, soybean aphids had a large flight with large captures at several locations. There seems to be high numbers of thistle aphids this year and populations of damson-hop aphids have developed as well this year. Populations of potato aphids persist and the small grain aphids (bird-cherry oat, corn leaf and English grain aphids) continue to be well-represented in trap catches. Because many of these are efficient vectors, the PVY Vector Risk Index has risen this week to also be pretty much the same as this time last year.
Many seed fields are being vine killed and harvested. But remember, aphids will continue to probe any green plant material in the field, so inoculum can be moved until plants are killed.
Hope harvest goes well, keep an eye on the fields...
If you have a field where Colorado Potato Beetle aren’t being controlled by insecticides, please let us know. We’d like to get samples of that population to test for insecticide resistance. Contact Ian MacRae at 218-280-9887.
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 August 21, 2020.
Cumulative PVY Vector Risk Index to August 23, 2019 season (for comparison)