Trap Catches Aug 09-Aug 16, 2024.
With 11 traps reporting, the average number of aphid vectors captured per trap across the region remained similar to last week. There were, however, some important differences; the average captures of small grain aphids was slightly below last weeks, while the numbers of soybean aphids increased, especially at two trap locations. Our PVY Vector counts and PVY Vector Risk Index values remain behind those of 2023, and we continue to see very similar levels as the 12-year average for number of vectors per trap and PVY Vector Risk Index. The top graph below is the current regional average PVY Vector data to 08/16/2024, 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.
Soybean aphids continue to increase as their seasonal dispersal continues. This will likely continue until our nightly temperatures drop into the 40'sF. Green peach aphid captures increased over last week, and were captured from 4 locations, with the trap at Becker, MN returning 6 of the wee beasties. Small grain aphid numbers were lower than last week, which is not surprising given many locations are already harvesting wheat. As with last week, many of the aphid species recovered do not colonize potato. So, we'll keep counting for now.
Bottom line - The aphid populations were off to a slow start but we are now very close to the average 2012-2023 averages. The recent rains in some of our locations may slow aphid population growth but the 12-year average population declines don't occur until the end of the month.
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 8/16/2024 Cumulative Aphid Species Capture and PVY Vector Risk Index to 8/16/24
