Friday, August 10, 2018

Aphid Alert 8-10-2018

Trap Catches Identified to August 10th


Looks like we have another big aphid week, folks!

We recovered a total of 301 aphids, 263 of which were vector species. In terms of aphid species, we are continuing to see a high diversity among those captured. This week, we recovered total of 15 different aphid species from 14 of the 16 sites reporting. We are seeing our heaviest flights in Grenora (80), Crookston (37), and Perham (36).

Last week, we recovered 130 total aphids, with the week before that topping off at 55 total aphids. Based on this trend, each week we are doubling the number of captured aphids. We saw this same trend occurring last summer towards the end of July to mid August, including a spike in cereal aphids. This does make sense, however, due to the maturing of grain which will lead to aphids seeking out better suited host plants.

We also recovered 2 Green Peach Aphids, one from Nebraska and one from Tappen.  Other aphid species captured included English Grain, Potato, Bird Cherry Oat, Pea, Buckthorn, Corn Leaf, Turnip, Greenbug, Thistle, Cowpea, Blackbean, Sunflower and Foxglove aphidsSoybean aphids were captured at Crookston (1), Nebraska (1), Perham (7), Sabin (1) and Staples (2) - so we're continuing to see movement across a broad area.

Josie noticed more winged aphids landing on her in the field, so had an idea that this week we'd see an increase in aphid numbers. This time of the year, there can be large flights coming into a field in search of better host plants, so population numbers can greatly increase in a matter of days. Some of our vector species, like Soybean aphids, don't colonize potatoes (deposit daughters on plants), so actually finding an aphid on a plant is rare compared to often a winged aphid may actually be visiting plants in the field (an advantage of suction traps, sucks 'em up as they're passing!)   Finding non-colonizing winged aphids on plants generally indicates there's a lot of movement going on.

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).

Cumulative PVY Vector Risk Index Map to August 10th, 2018

Cumulative PVY Vector Risk Index Map for 2017 
(included for comparison)

Aphid Species Capture + PVY Risk - Week of August 5th, 2018

Total PVY Risk and Species Capture to August 10th, 2018