Trap Catches Identified to June 26, 2020.
The season Aphid Alert Trapping season has started. This year we have 20 traps established and 5 reporting this week.
The season has started slowly. Traps in 5 locations have reported weekly captures and vector numbers are low to this point. Only Crookston, Humboldt and Perham recovered vector species and the PVY Risk Index values are low.
Colorado Potato Beetle have been moving into fields, mating and egg laying has likely began in established fields. Time to start scouting for beetles, especially in fields where insecticides weren’t applied at-plant or where their efficacy is decreasing. Remember, early instar larvae (very small larvae) are susceptible to insect growth regulators, like Rimon, and it might be a good start. Likewise, contact insecticides. Like Torac, are going to be more effective earlier in the season when canopies aren’t as well established.
If you have a field where Colorado Potato Beetle aren’t being controlled by insecticides, please let us know. We’d like to get samples of that population to test for insecticide resistance. Contact Ian MacRae at 218-280-9887.
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 June 26, 2020.
Cumulative PVY Vector Risk Index for 2019 (for comparison)
Aphid Species Capture and PVY Vector Risk Index for the week ending June 26, 2020