Program makes inroads against Zebra chip
By John O’Connell
POCATELLO, Idaho — University of Idaho researchers have no plans to scale back on the intensive program they implemented in 2013 to track the tiny, winged insects that spread the crop disease zebra chip, despite a significant decline in infections.
UI Extension entomologist Erik Wenninger said the program has federal dollars available but will again need Idaho Potato Commission funding and continued cooperation from the industry to meet the same standards in 2014.
“Despite having a low incidence of zebra chip in 2013 and a low incidence of the bacterium (that causes it), I think it’s really important to get more years of data under our belt in order to get a full handle of the situation,” Wenninger said.
Zebra chip, caused by the Liberibacter bacterium, ruins potatoes by forming bands in tuber flesh that darken when fried. It first arrived in the Pacific Northwest in 2011.
In 2012, researchers monitored 14 growers’ fields and a field at the Kimberly Research & Extension Center, surrounding each field with 10 sticky traps to catch psyllids. Of 1,073 psyllids tested that year, 250 were positive for Liberibacter. In 2013, those 14 heavily monitored fields were supplemented with another 94 fields, each with four sticky traps.
The average number of psyllids found per card decreased from 0.56 in 2012 to 0.11 in 2013, and psyllid infection rates decreased from 23.3 percent positive psyllids to 2.7 percent. Few infected tubers have been found in the 2013 crop, following a 2012 crop with about 1 infection and certain fields with 3-15 percent infection rates.
“We’re told there’s pretty much zero zebra chip out there now in Idaho,” Wenninger said.
Though insecticide field trials were expanded in 2013, results were inconclusive due to light psyllid and zebra chip pressure. Next season, Wenninger said trials will likely involve inoculating plants in smaller plots.
Results were also inconclusive when UI analyzed processors’ data to study relationships between psyllid pressure and proximity to features such as waterways, greenhouses and dairies.
Idaho seems to be a “melting pot” of psyllid biotypes, unlike the Columbia Basin, where only the northwest biotype is prevalent.
Biotype distribution may be linked to a change in the Liberibacter strain present in Idaho from haplotype A in 2011 and 2012 to haplotype B in 2013. Differences in the strains are not fully understood.
Research conducted by UI Extension entomologist Arash Rashed in collaboration with Texas A & M AgriLife Research and Extension and USDA Agricultural Research Service scientists in Parlier, Calif., shows a single infected potato psyllid has a 50-70 percent success rate with transmitting the bacterium after 48 hours of exposure to a plant. When pressure was increased to four infected psyllids, the transmission rate ranged from 80 to 100 percent, Rashed said.
The research also found the amount of bacterium transmitted increased under higher psyllid pressure. Greater infected psyllid populations also correlated with elevated levels of certain phenolic compounds and glucose and sucrose in tubers, all associated with zebra chip symptoms.