Monday, August 10, 2015

Trap Catches Identified to 8-7

Aphid numbers remain high!  This is mostly due to large numbers of soybean aphid but we are seeing large numbers of english grain, blackbean, and buckthorn aphids in certain locations as well.  
We are seeing more green peach aphids in the traps, contributing to larger PVY Risk Indices.  Motley is on top this week with an index value of 23.49 followed by Ada at 13.91.  
Crookston, Erskine, Langdon, and Lake of the Woods are in good shape with risk indices at less than one.
As always, 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.

**NEW** PVY Vector Risk Index
As you’ve heard us mention, not all species of aphid equally transmit PVY and some are better at transmission than others (green peach being the most efficient vector of PVY).  So, the total number of aphids in a trap don't necessarily refelct just how much vector pressure there is at that location. We've created an index, the PVY Vector Risk Index, to compare aphid numbers and their relative efficiency as a vector compared to the Queen of PVY vectors (green peach aphid!).  Using averaged reference comparisons from the literature, we multiplies the number of each aphid species captured by the associated comparison 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.

8-7 table

8-7 graph