Friday, July 14, 2017

Trap Catches Identified to July 14


Welcome to the Aphid Alert update for the week ending July 14.  Eighteen sites are now reporting (one had a technical issue this week).

This looks like it could be turning into an aphid year.  The PVY Vector Risk Index is low, but rising in many locations.  Several traps had high catches this week and we're seeing a lot of diversity in the species being captured.  In some locations, this week's map is starting to look like last year's total PVY Risk Index map, and we generally get heavier flights starting the end of July.  

Six sites this week had trap catches containing more than 20 vectors of varying efficiencies: Humboldt (35), Ada (41), Crookston (49), Sabin (25), and Brooks (39) in MN and Hoople (26) in ND.  However, Green peach aphid (the most efficient vector) was recovered from traps in Perham, Crookston, Sabin, and Brooks. The presence of Green peach this year indicates we must have had a successful immigration flight in spring or early summer. 

This summer we're also seeing the return of our newest identified PVY vector, soybean aphid.  If you are growing soybeans this year, you may want to scout them for aphid.

Speaking of scouting, this is definitely a year for doing so.  If you haven't started, you should.  The increasing vector numbers also remind us that the use of crop oils (e.g. Aphoil, JMS Stylet Oil, etc) have been shown to significantly limit the transmission of PVY.  A tactic to definitely consider this year...

Remember, 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.

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).
Click on any figure to see full size version.

Cumulative PVY Vector Risk Index to Date

2016 PVY Vector Risk Total for Comparison
Weekly Catch by Location
Cumulative Species Catch to Date by Location