Monday, July 9, 2018

Aphid Alert July 6, 2018

Trap Catches Identified to July 6th


Welcome back from the holiday week, hope you had a great July 4th.  For the third week in a row, we have recovered few aphids with very little vector pressure. With 8 sites reporting, we recovered 3 total vectors - 2 from Perham and 1 from Lake of the Woods. We did find 1 Green Peach Aphid from Perham.

As we stated last week, recovering fewer aphids from the traps does not mean we should hold off or slow down on scouting. With the rain and standing water dissipating, that will leave open spots or sections of soil. These open spots are a huge target for aphids as they tend to be more attracted to plants directly next to bare soil.

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 Risk 7-06-2018

Cumulative PVY Risk 2017

Total Capture through 7-06-2017

Weekly PVY Risk 7-06-2018

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