Saturday, August 24, 2019

Trap Catches Identified to August 23, 2019


Aphid captures dropped this week with only 91 vectors being recovered from traps. With grain being harvested, the first flush of cereal aphids seems to be decreasing.  Numbers of English Grain aphids were down across the region, but numbers of Bird-cherry Oat and Corn aphids were rising (although far less than English Grain aphids over the past 2 weeks).  Green Peach aphids continue to be present in the region with two locations each capturing one of these highly effective vectors.

Ada remains the hot spot for aphid captures with 60 aphids being recovered this week, almost half of which were Corn Leaf aphids.  Soybean aphids are still being captured but numbers remain low. Black bean aphid and Cotton/ Melon aphids were some of the other more common aphids recovered in traps this week. 

With this week's catch, the PVY Vector Risk Index is still tracking closely to that of last year.  I have heard that some growers will be initiating vine kill in the next week.  Not a bad decision; the presence of green plant material means there can still be transmission of PVY.   Aphid dispersal events are continuing and scouting and oil applications are again strongly recommended! 
Aphid Fact of the Week - Throughout the growing season, the aphid vector species we follow reproduce asexually; there are no males, no eggs and offspring are deposited as live nymphs on plants that are appropriate food sources. 
In the late summer / fall, decreasing night temperatures, daylight hours and food quality will trigger the development of a winged generation of male and female winged, reproductive aphids.  These winged reproductive stages will attempt to disperse to specific plant species, often different plant species from those upon which they've feed throughout the growing season.  Sexual reproduction will occur on these plants (referred to as the Primary Hosts) resulting in eggs that will overwinter on the Primary Host. 
Some of the vector species of importance, including Green Peach Aphid, probably don't make it through our winters due to the lack of specific primary host plants species or adverse climatic conditions (it's not easy to make it through the Polar Vortex!)

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 23, 2019.

Cumulative PVY Vector Risk Index for 2018 (for comparison)

Aphid Species Capture and PVY Vector Risk Index for Aug 16-23, 2019

Cumulative Aphid Species Capture and PVY Vector Risk Index to Aug 16-23, 2019