Monday, July 2, 2012

Time to Start Scouting – Green Peach Aphid Present in Crookston Plots

For seed potato growers and others concerned about potential vectors of Potato Virus Y (PVY)
Winged Green Peach Aphid (GPA) were recovered from our suction trap at the UMN-NWROC in Crookston, these would have been flying during the past week.  There are also wingless green peach aphids in a high proportion of plants at the plot edges but at relatively low numbers.  For those of you who have not yet done so, it’s time to start scouting fields for aphids!

As a quick reminder, aphids are sap suckers, have live young (all female in the summer) and they have winged forms which disperse the colony to new areas and non-winged forms which build colonies on new plants.  When an aphid feeds, it sticks it’s straw-like mouthparts (called stylets) into the plant to suck up some sap and determine if the plant is a suitable host, if it is, the aphid will remain and feed for a period of time prior to probing a new spot on the leaf.  GPA is the most effective vector of PVY, a vector is an organism that can pick up the virus from one plant and transmit it to another (a virus transport system!).  PVY is what is termed a non-persistent virus, it is acquired from an infected plant within seconds by a vector, and the vector can transmit it to another plant immediately when the aphid probes.  When aphid populations are large, the virus spread can be rapid and extensive. 

To scout 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. However, the use of feeding suppressing insecticides and/or refined crop oils (see below) may reduce the transmission of PVY within fields. In table stock potatoes, a treatment threshold of 30 aphids /100 leaves should deter yield loss due to aphid feeding.

As mentioned, controlling the vectors of PVY with insecticides has not proved successful in managing the spread of the disease.  There has been recent research that indicates insecticides that function as anti-feedant compounds or feeding blockers, such as Fulfill® (Syngenta Crop Protection) and Beleaf® (FMC Corp.) applied when aphids are entering the field have shown some efficacy in decreasing the impact of PVY.  Another management tactic to decrease within field spread of PVY is the use of mineral oils, such as JMS Stylet Oil® or Aphoil®, which can prevent aphids from probing plants and appear to keep virus off of stylets.  These finely distilled oils should be applied at least once a week but twice per week appears more effective.

A good websites for info:

The link to the old Aphid Alert which ran from 1998-2003:
The old Aphid Alert had some very good info on aphid biology and identification:

Aphid Trap Updates will Follow weekly!!

Comments and questions will be answered (maybe a few days later, but I will answer!)