Mechanical harvesting has been used in a handful of Florida’s citrus groves for decades.

But a couple of innovations on the horizon could significantly improve the system at a time when production costs are skyrocketing and labor supplies are uncertain.

The optimism stems from the Environmental Protection Agency being close to registering an abscission agent after years of industry testing.

In addition, a University of Florida researcher says he thinks he’s found a compact harvester that will allow mechanical harvesting in high-density dwarf trees, which an increasing number of citrus growers are planting to help address citrus greening.

Important piece of the puzzle

Spraying an abscission agent on a tree is a key component of the mechanical harvesting system because it loosens fruit so that it will fall off more readily.

Jackie Burns, center director and professor at the University of Florida’s Institute of Food and Agricultural Sciences’ Citrus Research and Education Center at Lake Alfred, says a product she has worked with for 15 years finally is nearing registration.

A full registration package was submitted to the Environmental Protection Agency in January.

The compound, CMNP, is a chemical that originally was tested in the 1970s by the Florida Department of Citrus. But because of freezes in the 1980s, reduced acreage and an abundance of labor, pursuing an abscission agent became a low priority.

The program was revived in the mid- 1990s, and researchers screened more than 500 compounds submitted by several manufacturers.

Burns says she was fortunate to acquire some of the compound that previously was tested and include it in more recent tests.

“This one rose to top,” she says. “There was nothing as effective or selective as this compound.”

Spraying the abscission agent on Valencia orange trees three to five days before harvest loosens only the mature fruit.

The agent is citrus-specific and has no effect on other fruits or vegetables.

It helped remove fruit less aggressively and more quickly than anything else tested.

Only mature fruit targeted

The most significant aspect of the abscission agent is that it provides some selectivity, says Paul Meador, chairman of the Florida Citrus Commission’s Citrus Harvesting Research Advisory Council and president of Everglades Harvesting & Hauling Inc. in LaBelle.

When late-season Valencias are ready for picking in May and June, there actually are two crops on the tree—the ripe, current crop and the quarter-size green fruit for the following season. The abscission agent loosens only the mature fruit so it can be gently removed without affecting next year’s crop, he says.

“Without abscission, selectivity becomes a real problem when you get to Valencias,” Meador says. “It’s held us back from mechanizing further.”

Currently, growers must suspend mechanical harvesting around May 10 because the process removes too much of the green fruit, says Carson Futch, whose company, P&H Solutions Inc., serves as the mechanical harvesting consultant for Johnson Harvesting Co. in Wauchula.

The agent will allow mechanical harvesters to run for an additional 21 to 30 days, making them more efficient, he says.

It also will enable growers to be less labor dependent in the spring, when workers often move out of Florida and on to other growing regions.

In addition, the abscission agent will help early in the season, when the fruit holds especially tight to the trees.

“It will shine for us early and late,” Futch says.

The fruit removal rate could increase up to 15 percent by using the abscission agent, says Fritz Roka, associate professor and agricultural economist at the Southwest Florida Research and Education Center in Immokalee.

Since the compound causes scarring in the form of a cosmetic ring on the blossom end of the fruit, it’s only used for processing oranges, not fresh varieties, Burns says. But she is hopeful that the effect can be reduced, and eventually it will be available for fresh fruit.

An added benefit

Tim Spann, assistant professor in horticultural sciences at the Lake Alfred center, has found what appears to be an unintended benefit of an abscission agent in the mechanical harvesting system.

Using machine picking removes up to 250 percent more leaves, stems and dead branches than hand picking, he found. An abscission agent reduces the amount of debris to levels equal to or less than hand picking.

“An abscission agent would really knock that back,” Burns says.

It’s difficult to anticipate how much the compound will cost, but Burns says, “We believe that it will be manageable.”

Registration should be complete within the next year or so.

Smaller machines

Meantime, Reza Ehsani, associate professor of agricultural and biological engineering at the Lake Alfred center, says only about 7 percent of growers use mechanical harvesting methods. But that could change as growers switch to high-density dwarf trees.

“The good thing about small trees is that mechanical harvesting becomes a lot easier,” he says.

Instead of the massive machines that cost more than $1 million apiece, growers can use smaller, less-expensive machines, such as an over-the-row olive harvester from Oxbo International Corp.of Byron, N.Y., or a blueberry harvester from BEI International LLC of South Haven, Mich.

Roka says the smaller machines would cost about $300,000, plus $100,000 for two “goats” to service them.

In tests, the smaller harvesters with no modifications were used on a couple of rows of dwarf trees.

“The result was very encouraging,” Ehsani says. The machine removed up to 95 percent of the fruit easily. In some cases there was some tree damage because the machine’s tree entrance tunnel was not designed for citrus.

The results should be even better if the machines are modified, such as changing the dimension of the shaking mechanism, installing conveyor belts appropriate for citrus fruit, and adjusting the shaking frequency and amplitude.

Ehsani says he plans to demonstrate one of the smaller machines at a mechanical harvesting field day next spring.

Huge potential

“The potential for mechanical harvesting is huge,” Roka says.

The key is getting them built and used over sufficient acreage that economies of scale take over.

With 85 percent of a crop going into a trailer, growers should be able to save 25 to 30 cents per box compared with hand-picked citrus, he says.

Despite slow progress and even occasional setbacks, mechanical harvesting eventually will take hold in Florida, Meador predicts.

“We’ve seen the transition in many other areas, from sugar cane to grape harvesting,” he says. “It’s just a matter of time.”

Mechanical harvesting symposium set for April

The University of Florida Institute for Food and Agricultural Sciences has scheduled an International Symposium on Mechanical Harvesting and Handling Systems of Fruits and Nuts, April 2-4, 2012, at the Citrus Research and Education Center in Lake Alfred.

The event, sponsored by the UF/IFAS Citrus Mechanical Harvesting & Abscission Program, is designed for scientists, growers, harvesters, handlers, processors and others interested in the practices and concerns associated with the technology.

Topics during the two-day symposium include harvesting systems, abscission aids, harvesting aids, robotic harvesting, automation and new machine designs.

The third day will feature an optional tour of mechanical harvesting of citrus and other crops in central and southwest Florida.

For symposium information, call Jim Syvertsen, faculty organizer, at (863) 956-1511 or e-mail

For registration information, call Sharon Borneman, conference coordinator, at (352) 392-5930 or e-mail Early registration deadline is Jan. 20.