Eye on psyllids
One year, it's the potato tuber worm; another year, it's the beet leafhopper. This year's public enemy insect is the potato psyllid. At both the Idaho Potato Conference and Washington/Oregon potato conference, the psyllid was foremost on the agenda of everyone attending.
Last fall's discovery of potato psyllids and zebra chip disease transmitted by psyllids in the Columbia Basin, Hermiston, Ore., and across the Columbia River in McNary, Wash., has grabbed the undivided attention of growers throughout the Pacific Northwest.
It's not as if psyllids just arrived in the United States. According to USDA-Agricultural Research Service's (ARS) Joseph Munyaneza, Ph.D., they were first found in Saltillo, Mexico, in 1994, and they crossed the border into Texas in 2000. Munyaneza spoke at both conferences on potato psyllid and zebra chip disease.
Munyaneza, a research entomologist at the at the Yakima ARS lab, described the aboveground symptoms of a psyllid infestation as resembling severe potato leafroll virus (PLRV) with leaf scorching and necrosis. When growers see these symptoms, they have to make positive identification prior to applying treatment - if it is a psyllid infestation, their efforts at treating the disease as PLRV will be a failure.
Psyllids can be the vector for transmitting the bacteria Candidatus Liberibacter to potatoes. Potatoes infected with the pathogen liberibacter will display zebra chip symptoms three weeks after inoculation. Foliar symptoms resemble PLRV, Potato mop top virus and PVY. Tubers will exhibit brown discoloration in the flesh, and upon frying will turn dark brown with splotches or streaks.
Munyaneza's research has determined that psyllids acquire liberibacter either by feeding on an infected plant or through birth from an infected female.
Munyaneza said that ZC-infected seed tubers do not transmit the disease, but they are slow to sprout, producing hair sprouts and weak yields.
Harry Strohauer, a grower in La Salle, Colo., has had firsthand experience with psyllid infestation. Strohauer estimates that he lost almost 90 percent of his potato crop to psyllids in 2010.
Advice for growers
Strohauer's advice for growers is to be pro-active and to monitor psyllid patterns.
"Once it's become an issue, you can't treat for it," Strohauer said. "You have to assume you're going to have psyllid, and treat for psyllid."
Strohauer said it's best to apply a systemic treatment in-furrow, so if you end up with psyllids your plants can withstand the pressure from the insects. He said that he uses Admire or Platinum in-furrow during planting, followed by Fulfill, Movento, Scorpion and Agri-Mek during the season, depending on the severity of the psyllid population.
Strohauer said he monitors the wind currents, places sticky traps in every field and pulls 100 petioles a week from each field when checking for psyllid infestation.
"Our program consists of monitoring everyone to the south of us," he said. "You have to decide what your program is going to be. Monitor the sticky traps and the petioles until vine kill. If it doesn't look like it's going to be one of those intense years, we'll begin to let up on our treatment."
Speaking at the Washington/Oregon potato conference, Alan Schrieber, president of Agriculture Development Group, said 2011 losses due to zebra chip in the Pacific Northwest were in the millions of dollars.
Schreiber said that at this time, there are more questions than answers about psyllids. They assume it overwinters and migrates into the Pacific Northwest, but Andy Jensen, director of research for the Washington State Potato Commission, found live psyllids on a bitter nightshade plant in a ditch in the Boise, Idaho, area in December.
Schreiber said there is no integrated pest management plan at this time, and urged growers to use neonicotinoids cautiously. He also emphasized that growers should limit the use of any insecticide to no more than two successive applications.
"You can't use neonicotinoids as a pre-emergent," he said.
He stressed that they can't let psyllids develop into a breeding population.
Schreiber presented two modes of action for growers to consider in controlling psyllids.
One at planting, with Admire/Gaucho mixes or Platinum/Cruiser mixed in-furrow, followed by Movento applied 70 days after planting, and MSO, followed again by Movento, applied 10 to 14 days later with MSO; followed by Agri-Mek, followed by Fulfill.
The second mode of action was a foliar program based on psyllid detection 50 days after planting. First application is Agri-Mek, followed by a second application of Agri-Mek; Fulfill, followed by Fulfill; Radiant, followed by Radiant; Provado, Actara, Venom, Belay or Assail twice, followed by Rimon twice.
--Bill Schaefer, managing editor