Friday, July 21, 2023


Trap Catches to July 14-21, 2023.

With 14 traps reporting, we've seen a jump in aphid number this week.  A total of 81 PVY vectoring aphids were recovered.  Leading the vector species were English grain aphids and soybean aphids.  Much of the small grains are starting to mature with an associated decrease in food quality (from the aphids' point of view) and we can expect to see increasing numbers of grain aphids being capture in the traps.  Soybean aphids seem to also be on the move.

Our populations are similar to last year at this time and very close to the 2013-2020 average.  In most years, our aphid populations tend to rapidly increase through August.  During the growing season, aphids are all female and give birth to live daughters.  Colonies of aphids you find on plants are generally non-winged; they feed, have daughters and grow the colonies.  Crowded or a decrease in the food quality of their host plants triggers the development of winged forms that disperse to establish new colonies.  As average daily temperatures increase, aphid populations will tend to reproduce more rapidly, leading to increasingly dense aphid populations on host plants.  Consequently, the maturing hosts colonies feed upon through July and the associated higher temperatures drive the development of aphid colonies.  As the population gets larger, they not only get more crowded but feed more on their host.  The result is the creation of winged forms in multiple species during August.

Consequently, we may continue to see increases through the coming weeks. 

So, you 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).

Click on any image below for full-scale version.

Cumulative PVY Vector Risk Index to 7/21/2023

Cumulative PVY Vector Risk Index to 7/22/2022 for Comparison

Aphid Species Capture and PVY Vector Risk Index for the week ending 7/21/2023

Cumulative Aphid Species Capture and PVY Vector Risk Index to 7/21/2023