Friday, August 25, 2017

Trap Catches Identified to August 25


Welcome to the Aphid Alert update for the week ending August 25.  Trap catches took a drop this week but numbers are still relatively high compared to last several years.  The average catch per trap last week was approx 67 vectors per trap location, although that was heavily influenced by two locations with over 500 aphids between them.  Even dropping those two traps out of the calculations, the remaining traps still averaged 33 vectors per location.  Traps this week averaged just 21 vectors per location.  The total trap catch for 2016, however, averaged only 29 per location for the entire cumulative season!  

The number of Green Peach Aphids (GPA) were down this week but 7 sites still captured a total of 9 GPA.  Soybean aphid numbers were also down this week but both Bird Cherry Oat and Corn Leaf Aphids, coming out of small grains, were still relatively numerous. 

Given the number of PVY vectors still present and flying across the entire region, it's important to remember that most of our PVY transmission occurs in the later part of the season.  Aphids leaving other host crops as they decline move to crops that are still green.  This would be a good year for early vine kill; if fields haven't yet been killed, this would be a good time to think about it.  

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