Friday, July 28, 2017

Trap Catches Identified to July 28


Welcome to the Aphid Alert update for the week ending July 28.  The aphid year continues - with a vengeance!

Trap catch did vary slightly this week; some reporting record numbers while others not so much. The PVY risk index skyrocketed in some sites due to high vector capture. Vector numbers were up at Brooks (81), Gully (35), Moran (25), McVille (84), Hoople (92), Staples (39) and this weeks big one - Humboldt with 183 vectors.  A few Green Peach aphids were present as well in Staples (4), Humboldt (3), Gully (2) and Hoople (1).

This year continues to be a high vector year. Soybean aphids are still on the rise in some soybean fields throughout much of MN.  Some of these populations continue to show pyrethroid resistance. Meaning that some fields still aren't quite getting adequate control. This may add to the number of soybean aphids moving into seed potato production areas.  While soybean aphid does not colonize potatoes, it is indeed a vector. So remember to keep your eyes open. We have started to test for soybean aphid resistance in some NW MN fields. We are looking for samples from sites that are reporting levels of resistance. That way we will have a better idea of both where we are seeing this resistance as well as what the actual level of resistance is.

Scouting obviously should be on the To Do list by now.  Due to another week of  high vector catch numbers, crop oils are still highly recommended. Data shows that narrow range mineral oils (e.g. Aphoil, Stylet Oil) applied at least once per week can significantly decrease the spread of PVY (twice per week is even better).

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 figure to see full-size version.

2016 PVY Vector Risk Total for Comparison

Weekly Catch by Location

Cumulative Species Catch to Date by Location