Wednesday, August 9, 2017

Trap Catches Identified to Aug 04


Sorry last week's report is late, we've had some technical difficulties!  This is officially a high aphid year!  With the increasing numbers of vectors, we strongly recommend scouting and the use of crop oils.  Anti-feeding insecticides should be applied if required (see below).

We continue to see high aphid numbers as well as an increasing PVY risk index. Sites that had high vector numbers include: Ada (282), Brooks (164), Crookston (99), Gully (116), Hoople (199), Humboldt (108), Lake of the Woods (86), McVille (145), Sabin (176), Staples (149) and Verndale (159). Meaning that in 11 of 16 traps reporting this week, we had high numbers.

Green peach aphid was found in 5 locations as well, including: Gully (1), Humboldt (3), Lake of the Woods (2), Sabin (2) and Verndale (1).  Small grains are maturing so we're also seeing an increase in small grain aphids (Ada had 219 Corn Leaf Aphids in their trap this week).  Soybean aphid numbers remain up, with the current outbreak of soybean aphid in MN & ND, we can expect large numbers of these insects to be moving into seed potato fields.

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.
Total 2016 PVY Risk Index for Comparison
Weekly Trap Capture by Location
Cumulative PVY Risk To date by Location

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