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In his study of the preharvest use of 1-MCP (methylcyclopropene) on apples, Dr. Jim Schupp observed some phytotoxic issues in Golden Delicious that "caused us a great deal of concern."

The University of Pennsylvania horticulturist said that he had never before had any phytotoxicity problems with MCP, so the phytotoxicity issues were alarming.

Most of the fruit cracking injury was found from dilute applications using the handgun and air blast sprayer, he explained.

Further study showed the phytotoxicity was related to the interaction of MCP and the application of captan/oil made for summer disease control. "It was not anything to do with MCP, but it was the interaction with MCP and captan and one percent oil that was used for summer disease control," he said, adding that the oil was mixed with Harvista to increase efficacy.

Schupp noted that they had a similar cracking incidence with Gala apples. While phytotoxicity issues were not detected at harvest in the fruit, after regular air storage, about 25 percent of the Galas were out of grade due to cracking at the calyx end.

"Again, we believe this was related to the captan/oil issue," Schupp stated.

SmartFresh representatives attending the presentation commented that the company is working on a new formulation for 2009 to resolve the phytotoxicity and other issues. Different application methods continue to be studied.