Friday, August 30, 2019

Trap Catches Identified to August 30, 2019


Aphid captures were up from last week, with 151 vectors being recovered from traps. A wide variety of species were captured this week, including some efficient vector species. The capture of 14 Green Peach Aphids from 3 locations (Ada, Crookston and Syre MN) caused a big increase in the PVY Vector Risk Index values in those locations.  With this week's capture, we are tracking higher than last season's totals, with potentially 2 weeks of trapping remaining.  Some locations are vine killing this week and will discontinue trapping. 

Ada MN again led aphid captures this week with 100 total vectors being recovered, including 7 Green Peach Aphids! This caused doubled the vector risk index for that location. Several other important vector species were also recovered from the Ada trap this week.  Syre also recovered numerous vectors this week (37) including 6 Green Peach Aphids and also saw a increase in its 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 - Aphid species that colonize potatoes, including Green Peach Aphids, preferentially colonize the field edge first, later dispersing into the rest of the field.  This may be a response to the contrast of the green canopy to the bare soil at the headland of potato fields.  If that is the case, it underscores the importance of scouting and protecting plants until vinekill is complete.

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 30, 2019.

Cumulative PVY Vector Risk Index for 2018 (for comparison)

Aphid Species Capture and PVY Vector Risk Index for Aug 24-30, 2019

Cumulative Aphid Species Capture and PVY Vector Risk Index to Aug 30, 2019