Friday, July 5, 2019

Trap Catches Identified to June 21 - July 05


Welcome to the first edition of Aphid Alert for 2019!

We apologize for the late start this year, we had difficulties obtaining some of our supplies.

We had 4 traps responding in the first week of trapping, Crookston, Humboldt and Gully MN and Tappen, ND. We had significant captures of Damson-Hop and the closely-related Cannabis aphids last year.  Both are suspected vectors of PVY and so we'll be counting and reporting on both species this year.  

Other insect populations in potato are sporadic this season, with Colorado Potato Beetle numbers being very low in many locations.  But as plants have emerged in most locations and aphids are starting to fly, it might be useful to consider oil applications.

**NOTE - we mistakenly reported a trap return from Grenora last week.  Unusual, because Grenora hadn't yet started their trap! Turns out this was a vial from last year we had out for training purposes. OOPS!!
Corrected maps and data are below!!

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 July 05, 2019

Aphid Species Capture + PVY Risk - Weeks of June 21 - July 05, 2019