Friday, June 22, 2018

Kick off to Aphid Alert 2018 - June 22nd

Trap Catches Identified to June 22nd


Welcome to the 
inaugural 2018 Aphid Alert report! This year, we have 19 trap locations, including one new site in Grenora, ND.

So far this year, we have seen very few aphids and very little vector pressure. With 6 sites reporting, Perham did capture 1 Green Peach Aphid. Only 5 other vector species were recovered from the traps.

Aphid numbers are lower than they were at this time last year. There are a few factors at play that could explain a delayed start for aphids. A late spring and early dry conditions, as well as wind events, such as the one in the figure below below that could have brought that Green Peach Aphid up to Perham.  The winds bringing some aphid species (including Green Peach Aphids) into our area from the south have very specific conditions and have to terminate in rain. NOAA's Air resources Lab has a great online tool to backtrack wind events (HYSPLIT); we use this tool to check if certain wind events may be bringing aphids our way.

As the summer progresses, the various storm events as well as increasing temperatures may well causes the vector populations to rise, so we will make sure to keep you updated!

In the meantime, 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).

6/22/2018 Cumulative PVY Risk (click to enlarge)

2017 Cumulative PVY Risk (click to enlarge)

Weekly Catch 6/22/2018 (click to enlarge)

HYSPLIT Backtrack of wind events ending with a rain event on May 29, 2018 (click to enlarge)