Trap Catches to Aug 18 - Aug 25, 2023.
With 9 trap locations reporting this week, we've seen a big drop in capture numbers. Not only are total regional captures are down (not surprising as some locations have vine killed), so are the average captures per location. Last week , average vector counts per trap were 55.7, this week an average of only 23.7 vectors were captured per trap. Some important vectors were recovered but the average per trap increase in the PVY Vector Index decreased as well from last week. As we move into September, hopefully aphid vector numbers will continue to decrease.
Green peach aphids (GPA) were again recovered in several sites this week and average numbers per trap were slightly higher than last week. Average English grain aphid numbers per trap were only 20% of last week. Soybean aphids, while still numerous and widespread were down by 60% per trap. Most other vector aphid species saw either a decrease per trap or stayed roughly the same as last week. Total regional vector capture this week was only 213 compared to last week's 780; this makes the average per trap capture 23.7 vector aphids per trap compared to last week's average of 55.7/trap.
While this is good news overall, it should be noted that as long as vines are green, aphids will be attracted to feed on them. Consequently, without vine kill, the potential for transmission of virus still exists. it's still advisable to practice the appropriate precautions.
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 8/25/2023
Cumulative PVY Vector Risk Index to 8/25/2022 for Comparison
Weekly Aphid Species Capture and PVY Vector Risk Index for all sites reporting the week ending 8/25/2023
Cumulative Seasonal Aphid Species Capture and PVY Vector Risk Index for all sites to 8/25/2023
