Trap Catches Identified to July 24, 2020.
Even though aphid numbers increased this week, they remain low with 24 vectors recovered from 9 sites of the 17 sites reporting this week. We started to recover soybean aphids from a number of sites as well. All the data's below in the tables.
PVY Vector Risk Index is now lower than this time last year. Small grains continue to mature and we have not yet seen a flight of cereal aphids, so this may change in the next week or two. Overall, however, the aphid numbers appear relatively low this year..
But the presence of winged aphids does signal the continued need for scouting, we do have movement of aphids into potatoes. If you're not already, it's time to be scouting seed (and commercial) potatoes for aphids.
Many of the species we're recovering are non-colonizing species, meaning they may not show up when sampling potato leaves. But their habit of moving through fields, probing plants to assess host suitability means they are still a problem!.
Aphid Fact of the Week - There are two different types of adult aphids; winged and non-winged (referred to as alate and apterous forms respectively). The winged aphids are dispersal forms. In summer, they're the individuals who leave colonies that are becoming stressed from densities or decreasing food quality. In the late season, winged aphdis will return to overwintering hosts. The non-winged aphids are colony builders, they feed on host plants, give birth to live daughters and increase the size of the colony. A winged aphid's daughters will always be non-winged.
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 July 24, 2020.
Cumulative PVY Vector Risk Index for 2019 (for comparison)