Phacidiopycnis rot has a watersoaked appearance in its early stage. It can begin at either the stem or calyx of the fruit.
Pacific Northwest pear growers didn’t know they had Phacidiopycnis rot in their orchards until Israeli quarantine officials began rejecting infected fruit several years ago. In its early stages, the disease looks similar to gray mold.
It turned out that the disease was widespread in orchards throughout Washington and Oregon. Dr. Chang-Lin Xiao, plant pathologist with Washington State University in Wenatchee, estimates that it is found in more than 95 percent of orchards in Washington’s Wenatchee Valley, where most of the region’s d’Anjou pears are produced. “It’s very common,” he said.
The fungus that causes Phacidiopycnis overwinters in the orchard on dead tree bark or in cankers. Close to harvest, it colonizes pear stems. Infections are more likely when the weather is wet as harvest approaches.
Infections might not be apparent at harvest, or even when the fruit is packed. The fungus can be on the stem or calyx tissue without causing decay.
But when the fruit is held in temperatures warmer than cold storage, the fungus grows into the flesh of the pear and causes decay. Unlike gray mold, which turns the flesh of the pear brown, this type of rot has a watersoaked appearance at first, later turning brown to black.
At the time of shipping, producers might not know there’s a problem, but when it arrives at its destination, the infection might be obvious, Xiao said.
And that’s what happened when Israel first rejected fruit with the disease in 2000, said Dr. Mike Willett, vice president for scientific affairs at the Northwest Horticultural Council. The container had been held in a port for a time without refrigeration, and when it was opened in Israel, the disease was quite advanced with black pycnidia (the fungus’s fruiting bodies) covering the fruit.
The disease has been a continuing problem. Rob Peterson of Duckwall-Pooley Fruit Company, Hood River, Oregon, recounted during a meeting of the Pear Bureau Northwest’s export committee last summer how one load of pears was rejected by Israel and transshipped to neighboring Jordan. But Jordan refused to accept the pears because the container had been opened in Israel and the fruit might be infested with fruit fly. It could not be returned to Israel because it had no phytosanitary documentation from Jordan. After several days stuck on a bridge between the two countries, the load was taken to a chemical dump site and the fruit was buried.
Israel, which is a pear-producing country, is a significant market for U.S. pears in the late winter and early spring when its own supplies are gone. But Mark Powers, vice president at the Hort Council, said packers should avoid shipping to Israel if there is evidence of a fungal infection on the pears. The transit time from the West Coast to Israel is 45 days.
“It’s very serious,” Powers said. “It’s the end of the line for a lot of shipping lines.”
Willett said the Hort Council hopes that the matter can be resolved by more rigorous inspection of the fruit before shipping.
Xiao said the disease can be controlled by drenching the fruit with a fungicide before it is put in storage. Packers in the Wenatchee Valley have generally avoided drenching pears because of the risk of infecting them with blue mold spores, which Mertect (thiobendazole, or TBZ) does not control.
But two new postharvest fungicides—Scholar (fludioxonil) and Penbotec (pyrimethanil)—can be used as a postharvest drench, and are effective against blue mold and gray mold, as well as Phacidiopycnis. “They can take care of all three postharvest diseases,” Xiao said.
However, disposing of spent solution containing the new pesticides has been a problem. Packers can apply the solution to land or use it for dust abatement under a special wastewater permit process with the Washington State Department of Ecology, but that requires extensive soil sampling and residue testing, Willett said.
Willett said this really shouldn’t be a disposal issue, but a registration issue. The registrants never envisioned that the rates that packers are using would be applied in a field situation and so the rates used for environmental fate studies during the registration process were lower than the rates packers are applying to land as they dispose of the chemicals.
Willett said the Hort Council believes it should be the registrants’ responsibility to deal with the issue as a condition of registration and to do high-rate studies.
Jansen Pharmaceutical is the basic manufacturer of pyrimethanil, which is marketed as Penbotec by Pace International, Cerexagri, and FMC. Syngenta is the registrant for Scholar.
Another difficulty in using the new chemicals is that they don’t have tolerances in some countries, including Israel. Israel considers the international Codex Committee on Pesticide Residues when developing its maximum residue levels, but it can take years for Codex to set the levels for new products.
As an alternative to a postharvest treatment, Xiao recommends an application of Pristine (boscalid and pyraclostrobin) before harvest, which he said has proven more consistent than Ziram in controlling the disease. However, Willett said Pristine does not have a residue tolerance in Israel either.