Friday, July 30, 2021


Trap Catches to July 30, 2021.

The aphid numbers decreased quite a bit this week - perhaps aphids don't like wood smoke!  The weather definitely had some effects on certain locations - apparently the Perham trap was blown over by powerful in-line winds - but our cooperators there got it set back up again.  

Unfortunately, the decrease in aphids was all in non PVY vectoring species (darn it!); the number of aphids that can vector PVY remain basically the same as last week.  There were, however, some small changes in what species were recovered.

English Grain aphids made up the vast majority of the vectors captured in suction traps.  Their continued presence probably reflects different planting dates for small grains this year.  There were slightly fewer Soybean aphids but they were recovered at several locations. Damson-hop and Cannabis aphids were both found in a couple of locations and Corn Leaf aphids are continuing to move as well.

The days are getting shorter but this is also the time of year when we typically have the greatest movement of aphid vectors and the greatest increase in risk of PVY transmission.  The graph below was calculated from our 12 years of Aphid Alert Trap data - it shows the average number of vectors recovered per trap by ISO-8601 week (a way of standardizing week numbers across all years).. 

Continued scouting is recommended, and use of crop oils and insecticides which stop feeding/probing may also prove necessary.  Remember, as long as there's green plant material, aphids will land and probe plants.  This means PVY can be vectored.  With the drought conditions and temperatures in several seed growing locations, care should be taken with oils to monitor for phytotoxicity.  

We will keep counting.  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 July 30, 2021

Cumulative PVY Vector Risk Index to July 31, 2020 (for comparison)

Aphid Species Capture and PVY Vector Risk Index for the week ending July 30, 2021

Cumulative Aphid Species Capture and PVY Vector Risk Index to July 30, 2021