Friday, August 12, 2016

Trap Catches Identified Week of Aug 08-12


Aphid vector numbers remain very low compared to last year, and the associated PVY Risk Index values are also not accumulating as they did last year.  But we have reports from SW Minnesota that the numbers of soybean aphids in fields there are increasing rapidly and many winged forms are being found.  Check out Bruce Potter's SW MN IPM Stuff newsletter at:
If you've got soybeans in, you really need to read Bruce's page!  He presents a lot of information about why you should still be scouting soybeans for aphids - time of year is a lot less important than plant stage for determining if soybeans are still susceptible to yield loss from aphids.

If we get some strong southerly winds, we could be looking at some major immigration events into the upper Red River Valley.  

Meanwhile, with the potential for immigrating soybean aphids, we're still not out of the woods.  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 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...

Aphid Alert Trap Catch Identified Week of Aug08-12
The Seasonal Aphid Alert Trap Catches for 2016