Friday, July 17, 2015

Trap Catches Identified to 7-17

As you’ve heard us mention, not all species of aphid equally transmit PVY.  While Green Peach aphid, Myzus persicae, is the most efficient vector of the virus, some aphid species don’t transmit the virus at all and many fall somewhere in the middle.  The table below contains the relative efficiency factors (REF), or how well each aphid species transmits PVY compared to green peach aphid.  The REF values we are using are averaged from the literature.  Because not all aphid species transmit the virus equally, the total number of aphid vectors at a given site does not give us the whole picture into the risk of virus transmission.  We have created a value, called the Relative PVY Risk Index, which multiplies the number of each aphid species captured by the associated REF to more accurately depict relative risk of PVY transmission.  Keep in mind, this is a snapshot in time, the Relative PVY Risk Index for any week just represents which site got the most aphids that are most effective at vectoring PVY.  The Index doesn't indicate which site will have the greatest risk over the season but should provide insight for making management decisions.
 ref chart

This week, our Forest River trap had the highest Relative PVY Risk Index and thus the greatest risk of PVY transmission.  This site collected one green peach aphid and 34 total vector species.  Despite having fewer vectors than some of the other sites, Staples had the second highest Relative PVY Risk Index because it captured 4 buckthorn aphids, the second most efficient PVY vector.   Crookston, Sabin, Stephen, Motley, Tappen, and Hatton all had PVY Risk Indices over one.  A couple of traps were down this week but should be back up and running for next weeks catch.
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.
 7-17 table7-17 graph