Friday, August 17, 2018

Trap Catches Identified to August 17th


Aphid vector numbers are down a bit from last week...

We recovered a total of 236 aphids, 206 of which were vector species. We're still seeing high diversity in the species captured, recovering aphids from 12 different aphid species from 15 of the 16 sites reporting. Hoople (42), Sabin (33), Ada (29), Gully (22), and the site in Nebraska (26) led the counts in trap captures this week.

Green Peach Aphids were up a bit this week (a total of 5 from 4 different locations) and the grain aphid counts remain high.  Perham received a fair number of Soybean Aphids, suggesting they got a southerly or Southwesterly wind, bringing aphids up from the more heavily populated soybean fields in the south. The PVY Vector Risk Index remains low as the season wraps up.  Here's hoping that transfers into a low PVY year!

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).

Cumulative PVY Vector Risk Index Map to August 10th, 2018

Cumulative PVY Vector Risk Index Map for 2017 
(included for comparison)

Aphid Species Capture + PVY Risk - Week of August 5th, 2018

Total PVY Risk and Species Capture to August 10th, 2018