Friday, August 5, 2016

Trap Catches Identified Week of Aug01-05


Aphid vector numbers still remain low in most areas as does the associated PVY Vector Risk Index values.  The annual Soybean aphid summer dispersal flight hasn't yet started, although numbers of soybean aphid are variable throughout MN and ND, most soybean fields are in reproductive stages, meaning we'll see more winged aphids developing from those fields.

While aphid numbers remain low, there have been reports of potato psyllids in western and south central ND.  These insects are the vectors of the Liberibacter bacterium that causes Zebra Chip.  We don't yet know if the psyllids recovered this year are infectious with ZC  but tests are underway.  Even psyllids not carrying the Liberibacter bacterium can injure potatoes via toxins in their saliva injected into the plant when they feed.  This can cause "Psyllid Yellows", characterized by yellow or purple leaves, reduced tuber number and size, malformed tubers, and chaining of tubers.  Scouting and management options are outlined in a Psyllid Management publication which will be posted on the NDSU Potato Extension Webpage (, 

Meanwhile. we're still not out of the woods for aphids...

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 Vector Risk 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 it's efficiency camopred 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 the map for full sized image...

Table of Trap Catches Identified Aug 01-05

Graph of Seasonal Trap Catches to Aug 01