Friday, August 3, 2018

Aphid Alert 8-03-2018

Trap Catches Identified to August 3rd


The vector numbers took a jump this week - aphids are starting to fly!  And, with apologies to Forrest Gump, this week's catch seemed to be summed up as: life is like a box of aphids, ya never know what yer gonna get....  

We recovered a total of 130 aphids,120 of which were vector species (15 different species!) from 13 of the 14 sites reporting. Sabin and Perham reported the heaviest flights with 32 and 24 vector aphids respectively.  

The number of species recovered in the traps this week was surprising, 
just about every vector aphid species we monitor was represented.  About 1/3 of the aphids captured were small grains aphids; no surprise there, even the latest planted grain is maturing and wheat harvest has begun, so grain aphids are seeking less senescent host plants. 

And the opening ceremonies for Sturgis are today (Aug 3) and our little 'biker bugs' are on the move (kudos again to Bruce Potter for coming up with the Sturgis Dispersal Event) and we're starting to see an increase in soybean aphid captures (although nothing like last year).  Soybean aphids were captured at Ballard (1), Crookston (1), Humboldt (1), Perham (1), Sabin (4) and Stephen (1) - so we're seeing movement across a broad area.  Populations in the soybean fields seems to remain low with only a few locations reporting populations at or above threshold.  

We also recovered 2 Green Peach Aphids, one from Sabin and one from Crookston.  Other aphids in the mix included Potato, Sunflower, Thistle, Cowpea, and Blackbean aphids.  Buckthorn aphids were also a frequent catch being recovered from 8 of the reporting sites.

This mixed assortment might reflect the colder nights we've been having lately.  In many species the movement from summer to overwintering hosts is triggered by temperature and photoperiod.  Cooler night temperatures can cause the development of a winged generation of adults whose purpose is to disperse back to the overwintering host.  Even in species that don't have their overwintering host here (such as green peach aphid), you'll still get those dispersal forms (aphids don't have access to Google Maps, they therefore have no idea their winter host isn't in the neighborhood).

So, numbers aren't that high but lots of different species out there - and they have to land somewhere.  So keep an eye on those fields...

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 to August 03, 2018

Cumulative PVY Vector Risk Index for 2017
(Included for comparison)

Aphid Species Capture + PVY Risk - Week of July 29, 2018

Total PVY Risk and Species Capture to August 03, 2018

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