Friday, August 18, 2023


Trap Catches to Aug 11 - Aug 18, 2023.

With 14 trap locations reporting this week, catches were down from last week (780 vector aphids this week, down from 891 last week).  However, due to the species captured, the increase in PVY Vector Risk Index was greater than that of last week (115.9 this week compared to 106.7 last week).  Much of this was due to greater numbers of green peach aphids being captured this week (23 this week compared to only 4 last week).  We are in a high vector risk year, far exceeding that of last year at this point.  In 2022, however, most of our vector capture came in the last two weeks of August.  Hopefully we won't continue that pattern. Our current pattern of trap catches does fit the pattern of the 2013-2020 average trap capture but is much higher (note the y-axis scale on the 2 graphs below). 

A total of 780 vector aphids were recovered in traps from August 11-14.  These included a rise in green peach aphid, the most efficient vector of PVY.  Green peach aphids were recovered from 6 locations, several of which were the same locations this vector was captured last week.  Soybean aphid captures were higher than last week, and, as with last week, were collected at all traps locations.  English grain aphids were recovered from all but one trap location and numbers were basically the same as last week (1 less...).  Potato, thistle, cotton/melon, and buckthorn aphids were all numerous and collected at most locations.   Many of these, especially green peach aphids, are very effective vectors of PVY, and their presence in high numbers skewed the PVY Vector Risk Index to be higher than last week's even though 110 more vector aphids were captured last week.  

As mentioned, last year's population mostly came on late in the summer, however, we've already exceeded both the cumulative number of vector aphids captured last summer.  Our PVY Vector Risk Index is also higher than last year's total.  The 2013-2020 averages do indicate late season increases are possible.  Hopefully the weather will cool, especially the night lows, and the populations will start to decrease.  But given the current situation, vector management is probably a good idea...

So, you keep scouting and we'll keep counting. 

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 8/18/2023

Cumulative PVY Vector Risk Index to 8/19/2022 for Comparison

Weekly Aphid Species Capture and PVY Vector Risk Index for all sites reporting the week ending 8/18/2023

Cumulative Seasonal Aphid Species Capture and PVY Vector Risk Index for all sites to 8/18/2023