Trap Catches Aug 02- Aug 09, 2024.
With 13 traps reporting, we saw another jump in aphid numbers; with a total regional increase of about 70% more vectors captured this week than last. The increased numbers were approximately even across all trap locations with the average increase in vector capture numbers being ~75%, with an average increase in PVY Vector Risk Index of ~43%. While our PVY Vector counts and PVY Vector Risk Index values are well behind those of 2023, we're still on track compared our 12-year average for average number of vectors per trap and average PVY Vector Risk Index values. The top graph below is the current regional average PVY Vector data to 08/09/2024, the bottom graph is the average PVY Vector data from 2013-2023. The X-axis is the ISO week of the year, the graphs are arranged so the ISO weeks correspond.
Much of this week's capture was soybean aphids (5 times as many as last week). As reported by Bruce Potter in his most recent IPM Stuff newsletter (sorry to see that go, it was always informative and entertaining! Thanks, Bruce for all you did!), soybean aphid populations have been rising in the south and the Sturgis Dispersal Event is underway (so called as it usually occurs right around the Sturgis rally time). So a lot of the southerlies we've caught over the past week have likely been bringing our little soybean feeding friends (fiends?) up here.
Green peach aphid captures were down this week, but many other species were up. Small grain aphids continue to be numerous and even the number of non-vector species of aphids captured doubled over last week. Most of the aphid species vectoring PVY are non-colonizing species, they won't leave behind nymphs and there won't be colonies to let you know they've been in the field. So, we'll keep counting for now.
Bottom line - it seems we're well into the typical August population increase for our area, and with the warming temperatures predicted for the next week, numbers will likely remain on the increase. Remember, aphid vectors will continue to probe potato as long as it's green; consider the potential for PVY transmission to be present until vine kill...
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).
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.
Click on any image below for full-scale version.
Cumulative PVY Vector Risk Index to 8/09/2024
Cumulative PVY Vector Risk Index to 8/11/2023 for Comparison
Aphid Species Capture and PVY Vector Risk Index for the week ending 7/26/2024Cumulative Aphid Species Capture and PVY Vector Risk Index to 7/26/24
