Friday, August 16, 2019

Trap Catches Identified to August 16, 2019


It's been another big week for aphids with 200 plus aphids being recovered in the traps - of course, almost 100 of those came from one trap (must have been a busy week for aphids in Ada, MN!).  Lots of cereal aphids and a few Green Peach Aphids again this week, and a real mix of species at several locations...

The trap at Ada, MN recovered almost 100 aphids this week, more than half of which were English Grain Aphid (this doubled the PVY Vector Risk Index values for Ada).  Cereal fields in the region have turned and are coming up on harvest, explaining the movement of cereal aphids.  Never-the-less, 58 English Grain aphids in one week was a big capture!  Other than that, Cotton/Melon and Thistle Aphids were captured at several locations.  Soybean aphids have also been increasing (but are still at very low numbers) at a number of locations.  Green Peach aphids were recovered at 1 location this week..  

The PVY Vector Risk Index has doubled again this week and is on track with last year's.  Seems 2019 is quickly making up for a low start.  

If potatoes still have green leaves, there can still be transmission of PVY.  Aphid dispersal events are continuing and scouting and oil applications are again strongly recommended! 

Aphid Fact of the Week - Many of our PVY vectors don't overwinter in NW MN and NE ND.  Those that do generally will be seeking overwintering hosts within the next month.  For many of these species, this will also mean the development of male forms and eventual sexual reproduction which leads to the production of eggs (the overwintering stage of many of these species).    

As always, 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).

Click on any image below for full-scale version.

Cumulative PVY Vector Risk Index to August 16, 2019.

Cumulative PVY Vector Risk Index for 2018 (for comparison)

Aphid Species Capture and PVY Vector Risk Index for Aug 09-16, 2019

Cumulative Aphid Species Capture and PVY Vector Risk Index to Aug 09-16, 2019