Friday, July 29, 2016

Trap Catches Week of July 25-29


Aphid vector numbers remain low in most areas.  Central MN had higher populations than others but even those were not as high as last year.  

There were no Green Peach and only a few Soybean aphids recovered from traps this week.   However, as Bruce Potter, IPM Specialist in SW MN, always reminds us, once you hear the Harleys making their way to Sturgis, you know the flight of the soybean aphid can't be far away...  He refers to that aphids summer flight as the Sturgis Dispersal Event, and according to Bruce's blog (IPMStuff), the SDE may be starting soon.  That means we may well see increasing numbers of soybean aphids coming our way.

For those of you suffering Colorado Potato Beetles, I sent out a short note on beetles and potential management options.  Dr. Andy Robinson was kind enough to put it on the NDSU Potato Extension website at:  

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 Vector Risk 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 it's efficiency camopred 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 the map for full sized image...

Here are the week's trap capture by table and the season's cumulative PVY Risk Index graph