Friday, July 20, 2018

Aphid Alert July 20, 2018

Trap Catches Identified to July 20th


There was a significant increase in aphid vectors this week; 51 aphid vectors (from 7 different species) were recovered from 11 of the 13 sites currently reporting.  This is a higher vector count than previously captured over the past 4 weeks COMBINED.  Ada and Crookston reported the heaviest flights with 20 and 10 vector aphids respectively.  

There were no Green Peach aphids collected this week but it appears that soybean aphids may be starting to fly (they recovered from Sabin and Ada in MN).  A few grain aphids were included in the mix as well.  As the grain matures and dries, the aphid population will respond by developing winged generations that will leave for, literally, greener fields....

These numbers have increased our PVY Risk Index in several locations and the appearance of Soybean aphid indicates that, if you haven't already started, it's time to start scouting your soybeans! The aphid season has begun, so keep your eyes open!

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).

Cumulative PVY Risk Index for the Week of July 16

Cumulative PVY Risk Index to the end of the 2017 Season For Comparison 
(Ie. How does the PVY Risk Index now compare to the end of last season?)

Weekly Capture 7-16

Total Capture + PVY Risk