Friday, July 21, 2017

Trap Catches Identified to July 21


Welcome to the Aphid Alert update for the week ending July 21.  The aphid year continues!

Trap catch was up in a number of locations and others are reporting steady populations, including some efficient vectors.  Vector numbers were up at Humboldt (32), Stephen (16), Brooks (37), Ada (28), Crookston (18), and Sabin (44).  A number of Green peach aphids were recovered this week as well; Humboldt (1), Staples (1), Stephen (1), Perham (1), Crookston (2), and Sabin (3).

Added to the high vector flight numbers, we have a few more curve balls... Soybean aphid populations are rising in NW MN with many fields nearing or already past treatment threshold.  A number of fields also have winged aphids, indicating the NW aphids are getting ready to move.  Some of the NW populations are showing pyrethroid resistance, meaning that some fields aren't getting adequate control and this may add to the number of vector species moving around seed production areas.  As we know, soybean aphid does not colonize potato but is a vector.  They'll move through the crop, probing plants to determine their suitability as a host.  Being disappointed, they will move onto the next plant candidate.  Being an insect and not very insightful, that next candidate is the neighboring plant.  They'll work their way through a seed field, probing and moving plant to plant, vectoring whatever inoculum is in the field.

Scouting obviously should be on the To Do list by now.  And given the high vector catch numbers, and the potential for more, the use of crop oils is strongly recommended.  Data shows that narrow range mineral oils (e.g. Aphoil, Stylet Oil) applied at least once per week can significantly decrease the spread of PVY (twice per week is even better).

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.

2016 PVY Vector Risk Total for Comparison

Weekly Catch by Location

Cumulative Species Catch to Date by Location