Washington potato farmers can expect high pressure from psyllids, the insects that can carry zebra chip disease, researchers say.
Potato psyllid populations fluctuate from year to year, said Rodney Cooper, temperate tree fruit and vegetable research leader for the USDA Agricultural Research Service in Wapato, Wash.
The psyllid populations that occur in potatoes in late summer correlate with psyllid populations that occur on matrimony vine, a non-native shrub, in early spring.
When researchers cannot find psyllids on matrimony vine in March, the psyllid pressure in potatoes remains low. During years researchers find psyllids on matrimony vine in March, psyllid pressure can be high in potatoes later in the summer, Cooper said.
"This year, we are seeing a very large number of potato psyllid in matrimony vine," Cooper said. "In fact, we are seeing perhaps three times more psyllids on matrimony vine than we did leading up to the 2016 potato psyllid outbreak. If 2021 follows the same trends we have seen over the last five or six years, then growers can likely expect a high psyllid pressure this year."
Matrimony vine was first brought to the Pacific Northwest by homesteaders in the late 1800s or early 1900s.
It is the first potato psyllid host plant to leaf out in the spring, Cooper said. Psyllids can complete at least one generation on matrimony vine before the emergence of potatoes. The plant survives the hot dry conditions of summer by going into dormancy, which forces the psyllids to disperse in search of new host plants, including potatoes.
It appears that matrimony vine is a source of psyllids arriving in potato in the region, Cooper said. But the plant does not appear to be susceptible to the zebra chip pathogen and therefore not a source of infective psyllids.
In fact, psyllid populations seem to lose the zebra chip pathogen when reared on matrimony vine in the laboratory, Cooper said.
"While matrimony vine might be a source of psyllids arriving in potato, matrimony vine might also be the reason why zebra chip disease is rare in our region," Cooper said. "Without matrimony vine, potato psyllids might utilize less favorable non-crop hosts that have potential to be reservoirs of the zebra chip pathogen."
Even though the region's zebra chip infection rates in psyllids are lower compared to other areas, about 1 in 10,000, years when there are more psyllids still increase the risk, said Carrie Wohleb, regional vegetable specialist.
"They'll probably show up earlier, too, so we have a longer period of having to watch them," she said.
The researchers will continue to monitor potato psyllids on matrimony vine in early spring, and use the psyllid counts to forecast psyllid pressure later in summer.
Growers should remain vigilant and assess their risks, Wohleb said.
"If it does come into any one grower's field, and they don't identify it until late, it could mean some pretty serious losses if it went unnoticed," she said.
March 31, 2021 at 07:30AM
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High psyllid pressure expected for potatoes this year - Capital Press
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