Welcome to the Aphid Alert update for the week ending September 01. Trap catches took a further drop this week but several trap locations are still reporting numbers well above last year's. The number of locations reporting is starting to decrease as well, with only 8 locations sending in samples this week.
Only two Green Peach Aphids (GPA) were recovered this week, 1 from Gully MN and the other from McVille ND. Ada led this week's trap catch with 75 vectors, followed by Perham with 22, Gully with and 20 and Lake of the Woods with 15. Al other reporting locations had trap catches in the single digits. PVY Vector Risk Index values are slowing but very high for the whole season. As mentioned last week, most PVY transmission in this region occurs in the later part of the season. Aphid flights are decreasing but still much higher than flights at this time last year! 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