Friday, August 11, 2023


Trap Catches to Aug 04 - Aug 11, 2023.

And another big week for aphid flights!  Only 11 traps were reporting this week.  Several have been negatively impacted by last week's weather and may need some maintenance to get back online.  However, with 6 fewer traps reporting, our numbers of vector captures this week is only slightly below that of last week's 17 traps.  So, while the average number of vectors captured is slightly lower than last week, the average capture per trap increased by about 30% (average trap catch of all aphids last week was approximately 66/trap; this week's trap captures averaged 92 total aphids per trap).  All things considered, it looks like aphid flights ramped up this week.  A large part of this week's capture were vector species and, accordingly, the PVY Vector Risk Index took a large jump.  

All traps reporting collected soybean aphids this week, some at very high numbers.   Three geographically separated sites sites reported green peach aphids this week, although only single individuals.  Very high numbers of English grain aphid were captured again this week, trap locations close to small grain production areas were hit pretty heavy and suffered an increase in PVY risk.  Potato aphids were common as were thistle, cotton/melon, and buckthorn aphids. A variety of other vector species were present in lower numbers.  The overall aphid flight included a large number of non-vector species.  

This is the second week traps recorded high flight numbers of vector species.  This looks very much like the start of a high vector pressure late season.  Most of our PVY transmission in MN & ND likely occurs in late season (certainly that is the time of highest vector flight) and higher vector population at that time does increase the potential for disease transmission.  Consequently, appropriate measures such as antifeedant insecticides and the use of crop oils should definitely be considered.

The weather next week may be turning a bit warmer.  That may mean more flight activity which will increase probing on plants in the field.  Those locations close to traps reporting any of the species that colonize potatoes (esp green peach, potato, foxglove, buckthorn, and black bean aphids) should continue to scout for colonies.  Although non-colonizing species can be as, or more important vectors of PVY, scouting may not provide good estimates of their potential presence in fields.  However, note their presence in local traps in the network and that will provide some indication.

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 8/11/2023

Cumulative PVY Vector Risk Index to 8/12/2022 for Comparison

Weekly Aphid Species Capture and PVY Vector Risk Index for all sites reporting the week ending 8/11/2023

Cumulative Seasonal Aphid Species Capture and PVY Vector Risk Index for all sites to 8/11/2023