Saturday, July 10, 2021


Trap Catches to July 09, 2021.

Aphid vector catch numbers increased significantly this week with the PVY Vector Risk Index values doubling in the past 7 days.  Cereal aphids are dispersing from the senescing small grains; most trapping sites reporting in the past week captured English Grain Aphids, and many reported Corn Leaf or Bird-Cherry Oat aphids.  Soybean aphids have also started their summer dispersal flight with most sites recovering low numbers of this aphid.  Cotton/melon and Buckthorn aphids were also recovered at several sites this week.  

The weather conditions still favor aphid population development and we expect further cereal aphid flight over the next couple of weeks.  The most numerous species reported this week are non-colonizing species, they don't become established on potato but they do enter potato fields and probe plants to assess if they're suitable food sources.  This probing is sufficient to acquire virus particles on their mouthparts.  After they determine potatoes aren't a viable food host, these aphids will fly to another plant, relatively close by and probe that one.  Non-colonizing aphids will work their way across a field trying plants and moving on.  Consequently, they will spread any PVY inoculum in the field.  Unfortunately, because they don't form colonies on potato plants, they're unlikely to be spotted with standard scouting techniques.  But colonizing species are being recovered as well, so it's still important to keep up the field scouting.

Increasing flights of colonizing and non-colonizing aphid vectors in our traps are good indications that the risk of PVY spread is increasing in the region.  The use of refined crop oils may well be a good addition to management practices (see below).

We'll keep reporting numbers.  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 09, 2021

Cumulative PVY Vector Risk Index to July 10, 2020 (for comparison)

Aphid Species Capture and PVY Vector Risk Index for the week ending July 09, 2021

Cumulative Aphid Species Capture and PVY Vector Risk Index to July 09, 2021 

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