Friday, August 18, 2017

Trap Catches Identified to August 18


Welcome to the Aphid Alert update for the week ending August 18.  The number of vector captured in traps dropped slightly this week compared to last (901 total vectors captured last week and 853 this week).  These numbers, however, still are very high and the PVY Vector Risk Index continues to rise steeply with weekly jumps far larger than total Index values from last year.  The PVY Risk Index maps tells the story pretty clearly, we're having a very heavy aphid year with high populations in most areas.  We strongly recommend scouting and the use of crop oils.  Anti-feeding insecticides should be applied if required (see below) 

Trap catches at two locations were still in the hundreds this week (Humboldt with 337 vectors and Ada with 209).  Green peach aphid is still being recovered from numerous locations, some in high numbers.  Soybean aphid flights continue in several locations with ND now seeing movement of these aphids.  Corn leaf aphids remain numerous and Bird Cherry Oat aphids are also starting to rise.  Sunflower aphids took a rise in several of the northern locations and Buckthorn aphid flights are rising as well.  Hopefully the increased movement of both Soybean aphids and Buckthorn aphids will soon represent movement back to the overwintering host of both of these species, Buckthorn.

The PVY Risk Index map, weekly counts and cumulative PVY Index values are attached below.  Be advised of the increases in your area.

Remember, keep scouting!

Scouting for aphids in potatoes:
·         Select leaves from the lower to mid canopy.
·         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 for Full Sized Version

Total 2016 PVY Vector Risk Index for Comparison

Weekly Trap Capture by Location

Cumulative Seasonal Capture & PVY Vector Risk Index by Location