Numerous potato psyllids collected last week in Idaho’s Magic and Treasure Valleys tested positive for Lso (liberibacter), the bacterium that causes zebra chip. Lso-positive psyllids were found in the following counties: Payette (1 field), Owyhee (1 field), Canyon (4 fields), Twin Falls (3 fields) and Jerome (1 field).
This represents a sharp increase in the prevalence of Lso-positive psyllids relative to prior weeks this season. University of Idaho researchers are fairly certain that these results are accurate; however, out of an abundance of caution to avoid reporting any false positives, they are in the process of re-testing several samples that did not show as strong a positive result as others.
Those sites collected during Week 9 believed to be positive are being re-tested and are marked on the linked spreadsheets as “pending” in the “% Lso+ psyllids” column. UI expects to update these data next week when results from the additional tests come in. Psyllids were collected that are believed to be positive but that currently have a status of Lso-“pending” in the following counties: Payette (2 fields), Owyhee (2 fields), Canyon (2 fields), Ada (1 field) and Jerome (1 field).
Regardless, there clearly has been an increase in the prevalence of Lso-positive psyllids as well as relatively high numbers of psyllids overall. Therefore, growers are urged to maintain their IPM programs targeting psyllids and to be on the lookout for plants exhibiting zebra chip symptoms over the coming weeks. Foliar symptoms should be manifested about three weeks following inoculation, but will need to be confirmed by examination and testing of tubers. Click here for a description and photos of zebra chip symptoms, and please take suspicious plant samples to the Kimberly R&E Center or to your local UI Extension Center.
Potato psyllids were collected this week on sticky traps in potato in the following counties: Malheur (Ore.) (1 field), Payette (3 fields), Owyhee (5 fields), Canyon (13 fields), Ada (2 fields), Elmore (1 field), Twin Falls (2 fields), Jerome (3 fields), Gooding (1 field), Minidoka (2 fields) and Cassia (6 fields).
Researchers collected 245 psyllids this week from sticky cards (179 from “light” sites and 66 from “intense” sites). Two potato psyllids were collected in a vacuum sample on an intense site in Canyon County, and four nymphs were found on leaf samples from an intense site in Ada County. Of the total 247 psyllids captured this week, 152 came from the Treasure Valley. Psyllids were found in 38 of the 103 fields (37 percent) sampled last week.
Detailed results from the “Intense” sites can be found here.