Apr 7, 2007

New Concept Cherry Harvester Has Its Debut

For years, cherry growers have worked with large trees.

It was a major challenge to contain their vegetative vigor and get them into full fruit production in less than six or eight years.

Now that growers can use dwarfing, precocious rootstocks, they need to learn opposite lessons ¬– how to promote vigor and reduce crop loads so as not to overtax the trees.

That assessment was made by Michigan State University (MSU) Horticulturist Greg Lang, speaking to growers at the second annual Cherry Variety Showcase at the Horticulture Research Station in Clarksville, Mich., July 7.

The event, designed to allow growers to taste and otherwise evaluate hundreds of sweet and tart cherry varieties, featured other components: Lang’s discussion of tree management, a visit to MSU’s new installation of high tunnels over a block of sweet cherries, and a look at a mechanical harvester that might be used to pick fresh-market-quality sweet cherries from the newer, smaller trees growers are planting.

Machine Harvest

The mechanical harvester was brought to Michigan by USDA Agricultural Engineer Donald Peterson, who has been working with it at the Appalachian Fruit Research Station in Kearneysville, W. Va., for a dozen years.

It was originally developed to selectively harvest ripe blackberries and other cane fruits for fresh market, he said, but that didn’t work out. However, the concept was used to build “an incredibly good” harvester for Florida juice oranges and another for picking fresh-market blueberries.

The machine worked well in blueberries, too, he said, providing quality as good as hand-picked, but some marketing glitches resulted in no machines reaching commercial fields.

After the showcase, visitors went to the orchard to see what this never-before-tried-on-cherries harvester might do.

It was very effective, easily removing all the tart cherries it could reach on standard-sized Montmorency trees. Since the machine was designed for berries, it couldn’t reach deep enough or high enough into the canopy to remove all the cherries, but it removed all the cherries it got close to.

That’s important, because this harvester doesn’t shake the whole tree. It just shakes what it touches.

The value of the shaker is being investigated by a team of researchers at MSU, who have obtained a grant to do it. The team includes ag engineers Richard Ledebuhr and Dan Guyer – who will evaluate how the machine works on the trees – and horticulturists including project leader Jim Flore, who will evaluate how the trees can adapt to the machine.

Initial tests, Ledebuhr said, were run using the harvester on different types of cherry trees maintained as part of the breeding work being done by Amy Iezzoni. Unlike truck shakers, this new shaker worked well on trees with willowy wood, on trees that were bush-like without large trunks or with low limbs under which trunk shakers would not fit, Ledebuhr said.

If the basic machine concept is good, then the horticulturists can adjust tree size, canopy shape and other factors to fit it.

Peterson called his machine a “direct-drive spike-drum canopy shaker.” Ledebuhr referred to it as a “mass balance finger drum shaker. “Whatever the name, the idea, Ledebuhr said, is for the two spiked drums to be shaken in such a way that when one pushes, the other pulls, transmitting action into the canopy and removing fruit.

The next step is to evaluate cherries shaken in this way to see if they can meet the hand-picked-for-fresh-market standards, Ledebuhr said. There are several reasons to think this can be achieved.

First, the trees can be shorter and lower to the ground. That means fruit doesn’t fall as far and doesn’t hit as many limbs on the way down, eliminating two sources of bruising.

Second, since not as much energy is put into the tree, cherries do less threshing about. While trunk shakers transmit enormous energy to the tree, this shaker was run by the equivalent of a lawn mower engine.

Harvesting in the demonstration was fast, too. The machine moved continuously down the row of cherries, never stopping or “indexing” as a trunk shaker would. In citrus, Ledebuhr said, the shaker worked so well growers remade their groves by hedging and blocking them into hedgerows.

There was no catching system on the demonstration machine, but Peterson said that part was no problem.

The machine is also being tested on sweet cherry trees in the Northwest, Peterson said.

Pruning for Balance

The new-style trees might better fit a fresh-market mechanical harvester, but growers have other things to learn just to manage the trees, Lang said. With the dwarfing Gisela rootstocks, “we need to promote vigor and reduce crop load. Crops become too heavy too soon,” he said.

Growers – and researchers – are trying to “prune for balance. What we do this year affects what happens two years from now,” he said.

Cherry trees bear on wood that is three years and older. In the first year they bear, fruit is supported by three-year-old fruiting spur leaves, which have seven to nine leaves per node; by non-fruiting spur leaves that are two years old and have six to eight leaves per node; and by new growth that has one leaf per node.

Thus, contrary to what it might seem, fruit on newly bearing trees are well supported by photosynthetic capacity. The ratio of spur leaf area to fruit clusters is about three to one.

Fruiting increases faster than leaf area. Fruiting can double in the second year, while leaf area increases much less, approaching a one to one ratio as the tree matures.

To keep a good leaf area, which Lang said is about 140 square centimeters per fruit, growers need to thin, fertilize and prune.

Heading cuts on younger trees increase leaf area by stimulating new growth of stem leaves and shortening the limb on which fruit is borne. Nitrogen fertilizer applied in the fall increases leaf number and size without increasing fruit set.

Lang is developing a computer model that can actually grow and manipulate a cherry tree on screen, showing the effect of pruning cuts and limb removal on tree production and health in future years.

High tunnels

At the Clarksville station, new Haygrove Tunnels were installed in June, too late for research this season but in plenty of time for next.

Haygrove’s Andy Crittenden talked about the benefits of growing sweet cherries under plastic: earlier fruit (from spring protection), larger and sweeter fruit (from letting them stay on the tree until full maturity), more fruit (from less frost damage and better pollination), less shipping cost to local markets and no cracking from harvest-time rain.

Pay-back time can be fast if a grower can harvest $10,000 worth of prime fruit from an acre instead of $4,000 in fruit damaged by untimely rains, he said.

Variety showcase

The Variety Showcase was organized in this, its second year, by Wally Heuser and Wanda Gale of International Plant Management, a company that searches for new and better varieties and propagates them for commercial production.

Heuser is the person who saw Gisela rootstocks at work in orchards in Germany and brought them to this country for evaluation and use.

Sweet cherries in the variety showcase included established varieties and varieties from test plots at MSU, Cornell’s Geneva Experiment Station and other sources. There also were red-fleshed “sweet tart” varieties from Europe, showing promise for sale in a fresh market niche here.

One variety that got a positive review is Regina, which was at perfect ripeness and was attacked in the orchard by visitors. Heuser said he thinks it has a future.

It has large, mahogany-red fruit, with good firmness and mild flavor. It is crack-resistant.

On the other side of the slate, it is not self-fertile and is “genetically a shy bearer,” Heuser said, and needs to be on a precocious rootstock. It blooms late and ripens late, making it frost-resistant but hard to pollinate.

Lang noted that many of the promising varieties are not self-fertile. Blocks of sweet cherries need to be planted with several varieties, three or four, to assure good pollination, even if mixed blocks don’t make harvest all that easy.

Wanda Gale said she is working with several dark cherries from Italy that are self-fertile and very low cracking. She is evaluating six varieties, the names of which end in Star.