Welcome to the Aphid Alert update for the week ending September 08. The colder weather has brought along at least one good thing, the aphid vector numbers took a real tumble this week. With only 6 sites reporting this week, only 34 vector aphids were recovered from across the area (that number was 244 last week!) Only one site had vector numbers in the double digits; Humboldt reported 12 vector species (compared to 93 last week). No Green Peach Aphids were recovered in the past week and Soybean Aphid numbers likewise were much lower. Many locations have already vine killed. 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).
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Total 2016 PVY Vector Risk Index for Comparison
Weekly Trap Capture by Location
Cumulative Seasonal Capture & PVY Vector Risk Index by Location