Trap Catches to Aug 12, 2022.
Another large jump in aphid numbers this week with an accompanying rise in the PVY Vector Risk. The increase through August so far for this year's regional aphid population seems to mirror the average population growth from 2013 through 2020. In other words, weekly captures are still increasing. The total numbers of PVY vectors are still only half what they were at this point last year, but if the weekly increase in numbers continues, our total counts could be close to 2021. The graphs below show the average regional weekly capture in 2021, the average regional weekly trap captures for this year, and the seasonal regional captures by week averaged from 2013 through 2020. Note that in 2021 (upper left graph), by August, weekly captures had peaked and were decreasing, this year (upper right graph), half way through August and our weekly captures are still increasing. The 8 year average pattern of weekly captures (bottom of the 3 graphs) indicates our typical peak occurs in August.
(Click on image for larger version)
Soybean Aphid numbers continue to increase, as do our cereal aphid numbers with Corn Leaf and English Grain aphid numbers taking a bit of a jump. Buckthorn Aphids were recovered from numerous trapping sites as were thistle aphids.
Another single Green Peach Aphid was recovered from the trap in Becker, MN and there have been potential recoveries in Manitoba as well. This indicates that there may have been at least a couple of immigration events this season. Green Peach Aphids do not overwinter this far north, and their populations are re-established from the south only by very specific low-level jet wind events. Looks like this has happened in at least two locations this year.
In any case, numbers are rising, vector species are present.
So... 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).
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 Aug. 12, 2022
Cumulative PVY Vector Risk Index to Aug 13, 2021 (please note different scale)
Aphid Species Capture and PVY Vector Risk Index for the week ending Aug 12, 2022
Cumulative Aphid Species Capture and PVY Vector Risk Index to Aug 12, 2022
