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The powerful instrument 1-MCP (methylcyclopropene) is used to retain the firmness of apples in cold storage. But the product also shows potential as a tool for producers to use in the field to better manage harvest, according to a University of Pennsylvania researcher.

Dr. Jim Schupp, horticulturist for the University of Pennsylvania, has studied the preharvest use of Harvista (MCP) for several years, focusing on Cameo and Golden Delicious apples during the last two years to compare rates, concentrations, and methods of application. Harvista, the trade name for the MCP product manufactured by AgriFresh, was registered in 2008 by the U.S. Environmental Protection Agency for field application. Various trials in commercial and research settings were conducted last season in both east and west tree fruit production areas.

Previous Harvista research conducted by Schupp showed essentially the same results when rates of 150 and 75 parts per million were used, which led him to target rates of 0, 35, 55, and 75 ppm in 2007 and 2008. "The year before, research showed that 75 ppm was as high as you needed to go, and that rates could maybe even go lower than 75 ppm."

Harvista was applied four days before anticipated harvest, with fruit evaluated for maturity seven and 14 days after harvest. Fruit was held in regular air storage for 60 days, treated with and without SmartFresh (MCP), and evaluated again after sitting at room temperature for one week.

Ethylene reduction

Schupp, who shared the data during winter tree fruit talks at the Great Lakes Fruit, Vegetable, and Farm Market Expo in Grand Rapids, Michigan, found a significant linear response to both sample dates for reduced ethylene production from the field applications of Harvista.

The field applications of MCP also slowed down the starch hydrolysis in fruit and slowed development of soluble solids. "It’s definitely slowing down maturity," he summarized.

For the fruit held in storage, the preharvest Harvista applications reduced ethylene production and Harvista-treated fruit maintained firmness better than the control of no pre- or postharvest MCP treatments. But he doesn’t see Harvista as a replacement for SmartFresh in storage settings. "If you really want to have a significant impact on storage ethylene, SmartFresh application following harvest is still the way to go.

"When we used SmartFresh, it didn’t really matter what we did, we still had firmer fruit in storage. But we did see a benefit with Harvista applications as we increased the rate up to 55 ppm and we slowed the firmness loss in those samples."

Tricky working with gas

Schupp also compared application methods, working to develop concentration rates for air blast sprayers in comparison to handgun sprayers used in research settings.

"Harvista technology is a little bit ticklish to work with because it’s a gas," he said, adding that nozzle pressure needs to be kept constant to prevent gassing off the material too quickly.

All treatments received 57 grams of active ingredient per acre, but he varied the gallonage of the spray tank (200, 100, 67, and 50-gallons of water per acre) and tractor speed (1.25 and 5 miles per hour) to test different treatment concentrations. For the sprayer comparisons, treatments were made four days before harvest of Golden Delicious. Fruit was evaluated 7, 14, and 21 days after harvest and fruit were held in regular air storage, with and without SmartFresh, as well as controlled atmosphere storage where all fruit received SmartFresh applications.

All treatments resulted in reduced internal ethylene production and helped stave off the loss of firmness at harvest. Similar patterns were noticed in the starch indexing of the fruit. He concluded that the air blast sprayer is effective within the range studied.

In the concentration studies with Cameo apples, Schupp found that fruit firmness was as good in the 55 ppm rate studied as in the 75 ppm. He believes that 50 to 55 ppm would be the bare minimum rate, and that a 75 ppm rate would provide a margin of safety for spray variations of application technology.

He believes that the preharvest use of Harvista will allow growers to better manage their crop, spreading out picking and harvesting 10 to 14 days later—and still have fruit with excellent storage potential. He observed excellent stop-drop properties from Harvista in 2008 in which it provided three weeks of drop control.

For those interested in enhancing fruit quality in storage, he believes SmartFresh is still the best tool. "Harvista has a place in storage if you just want to hold fruit for a short period under regular storage. It’s not as good as SmartFresh, but it will confer some benefit, particularly in terms of slowing the loss of firmness."

Schupp believes that the real benefit of MCP is its ability to work fast. "Regardless of whether MCP is applied to apples on the tree or in the storage room, it kicks in within hours—not days. It means that you can run that application close to your anticipated harvest date, and by doing so, that fruit colors and loses the real blocky textures and develops good eating texture. You can get that fruit right to the edge and then stop it there and come back in two weeks for harvest."