Monday, July 30, 2018

Aphid Alert July 27, 2018

Trap Catches Identified to July 27th


We are seeing a continuing trend of increased vector pressure this week; 43 aphid vectors (from 13 different species) were recovered from 9 of the 13 sites reporting this week. Sabin and Ada reported the heaviest flights with 12 and 9 vector aphids respectively.  

For the second week in a row, there were no Green Peach aphids collected.  We are, however, still seeing flights of grain aphid species. Soybean aphids were recovered from the traps at Ada and Ballard (1 from each location), There have been hotspots of soybean aphids reported from fields in several locations, including Crookston (although no local fields have been reported over threshold).  So keep monitoring for Soybean Aphids!

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 Vector Risk Index to July 27, 2018

Cumulative PVY Vector Risk Index for 2017
(Included for comparison)

Aphid Species Capture + PVY Risk - Week of July 22, 2018

Total PVY Risk and Species Capture to July 27, 2018

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