Trap Catches Identified to July 07
Welcome to the Aphid Alert update for the week ending July 07. Twelve of our 19 sites are now reporting and we expect the remaining 7 to be online by next week.
There were some aphids flying this week, but a lot of them were non-vector species. Overall, vector catch was relatively low but we did recover one Green Peach Aphid from Humboldt, MN, which also had several corn leaf aphids in their trap. The Crookston trap had the most diverse catch this week, while there was only one of each species, that trap captured soybean aphid, small grain aphids (English grain, Corn Leaf and Bird-Cherry oat aphids), a potato aphid, a turnip aphid and a Cotton/Melon aphid rounded out the vector count but they were all kept company by 9 non-vector aphids from 4 different species. While not the most numerous trap this summer (last week Gully had a total 21 aphids and was topped by the Ada trap which captured 43 aphids) it did take a while to ID everything in that jar!
To this point, the Vector Risk Index remains low, but with the increasing temperatures we can expect more activity in the coming weeks. So keep scouting...
Scouting for aphids in potatoes:
· Select leaves from the lower to mid canopy.
· 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 images for full sized versions...