Trap Catches Identified to August 02, 2019Greetings
Trap counts for the Aphid Alert Network continue to rise; higher catches were seen in all sites reporting. The Ada MN trap reported a total of 42 aphids from 8 different vector species. The Crookston, Gully and Staples trap sites all reported double digit catches of vectors as well. A number of different vector species were recovered but no Green Peach Aphids so far. As expected, a lot of sites were reporting cereal aphids, especially English Grain Aphid - this species seems to have had a good year...
The overall PVY Vector Risk Index values remain similar to those of last year but we are catching up... If aphid numbers continue to increase, the PVY Vector Risk Index could quickly rise.
Aphid Fact of the Week - Many aphid species, including many of the aphids that vector PVY, have a strong preference for eating a particular species of plant during the summer season. As our summer progresses and many of those plant species mature and their physiology changes, the nutritional quality of their sap decreases. Aphids, in response, will eventually develop a generation of winged aphids which will disperse, seeking food of greater nutritional value. This is why our aphid catches tend to rise later in the season and we begin to recover species like the cereal aphids.
As always, keep on scouting!
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 August 02, 2019.
Cumulative PVY Vector Risk Index for 2018 (for comparison)
Aphid Species Capture and PVY Vector Risk Index for July 19-26, 2019
Cumulative Aphid Species Capture and PVY Vector Risk Index to July 26, 2019