Friday, June 29, 2018

Aphid Alert June 29th, 2018

Trap Catches Identified to June 29th


This week the traps recovered very few aphids and there was very little vector pressure. With 6 sites reporting, we recovered 4 total vectors - 2 from Ada, 1 from Perham and 1 from Nebraska. Good news - no Green Peach Aphid this week!

We're seeing fewer captured aphids and lower vector pressure than at this time last year. However, vectors are present and if you haven't started scouting, you should.  If you have, keep it up! The storms that have rolled through in the past week can effect aphid numbers so scouting will be necessary to keep track of vector numbers.  Remember, start at the field's edge, aphids have a strong preference for settling on plants neighboring bare soil.  Also check plants bordering open areas within fields, holes of 1m diameter or greater can serve as a beacon for winged aphids.  With all the rain in some areas, we're going to see some open spots in fields....

Keep scouting and don't drown out there!

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).