In the December issue of Potato Grower magazine exactly a year ago, we reported on how zebra chip was spreading north—discovered the first week of Oct. in Idaho for the first time—and how non-infected psyllids had devastated crops in LaSalle, Colo., in 2010.
This year, Dr. Nora Olsen, University of Idaho associate extension professor in Kimberly, Idaho, updated aerial applicators in September at the Idaho Aerial Applicators Association Wet/Dry Clinic at the Gooding airport, on where we’re at with zebra chip.
She told pilots, who were in attendance to test their spray equipment and earn credits toward re-certification, that this year UI scientists scouted out areas that were hot spots for potato psyllids last year, putting out yellow sticky card traps.
The first psyllids were caught June 19. Some fields trapped psyllids on a daily basis while other fields hardly netted any, and hot spots were scattered all over the place—most of Twin Falls County, southern Jerome County and Murtaugh, just to name a few.
The first plants showed symptoms for zebra chip in mid-July—about on schedule for the expected three to five weeks to symptoms—on the edges on the fields. She points out this is problematic for aerial applicators, as there are typically houses and power lines in the way.
“We’ll probably see ground rigging coming back,” she says.
One thing she says they’re trying to better understand is the “why” behind the spots where psyllids are hot with the Liberibacter bacterium.
“In the Columbia Basin, the percentage of hot psyllids carrying this Liberibacter bacterium…is very low. We’re talking single digit percentages. In Idaho, we’re talking 30–50 percent are hot.”
She reports that they started seeing colonization in the fields in August, with the numbers skyrocketing in September.
“It’s going to be hard for us to figure out how to target those late flights,” she says.
She points out that there are two types of the Liberibacter disease—type 2 is found in the South and is a much more severe zebra chip. Type 1 has been found in California, New Zealand and the Pacific Northwest. It’s not as severe, she says, but it’s still doing a lot of damage.
Potato psyllids are not new to Idaho, but the disease is. She says it’s possibly a combination of migrating in and over-wintering, but they’re not sure.
We’re hoping for a harsh winter to see what that does to the population, and at pretty much all grower meetings and conferences this winter, Olsen will be encouraging growers to start this next year on a regimented spray program of the newer chemistries.
“We’re gonna have to be pretty strong from June up until vine kill, for sure,” she says.
Unfortunately, the jury is still out on the specifics.
“We’re still up in the air on what we need to recommend [for zc control],” she says.