WSU engineers are developing a vibrating actuator that will be used with a mechanical harvester to shake limbs and remove fruit without damaging the trees.
A four-year research project that aims to make sweet cherry production more efficient, profitable, and sustainable marked the halfway point with an informational meeting and tour for growers.
The four-year project is partially funded with a $3.9 million grant from the federal Specialty Crop Research Initiative and involves scientists and companies in Washington, Michigan, California, and Oregon. Horticulturist Dr. Matt Whiting and engineer Dr. Qin Zhang with Washington State University in Prosser are project leaders. Whiting said he hopes the project will be funded for at least a fifth year.
The project addresses the the entire supply chain from growing to marketing and has six main objectives:
1 Develop efficient orchard systems
New cherry growing systems must be more precocious and productive, Whiting told growers at the November meeting. The canopy and crop load must be precisely managed, and pruning and training must be simple and systematic. The canopy should form a compact fruiting wall that can accommodate new technology and improve labor efficiency and fruit quality. It should minimize the environmental footprint.
Whiting developed the Upright Fruiting Offshoots (UFO) system to respond to these requirements. With trees on Gisela rootstocks, there’s the potential for fruiting in the second year.
Nursery trees are planted at a 45-degree angle and then bent to horizontal. Buds are removed from the lower side of the leader, and upright shoots encouraged to grow on the top side every 12 inches or so. Bending the trees flat immediately after planting tends to promote overly vigorous upright shoots from the base of the trunk, he has found, so he now recommends waiting until the terminal shoots break. After the trunk is laid flat, the terminal shoot is either cut off or bent upwards to form an upright.
There are just two rules for maintaining the trees: 1) Cut out lateral growth coming off the uprights; 2) Take out the most vigorous uprights with renewal cuts.
WSU graduate student Antonia Sanchez Labbe has been testing different types of renewal cuts (flush cut, six-inch stub, or stub with one or two buds) at different timings (full bloom, postharvest, and dormant). She found 100 percent regrowth from the stubs with buds, compared with as little as 30 percent with some of the other cuts, and had most success at the full-bloom timing.
Labbe has tried applying the growth regulator Apogee to the shoot tips to control growth.
Research has also been done to compare the efficiency of various cherry training systems by monitoring the volume of fruit picked in a given time. Overall, the UFO and Kym Green Bush were the most efficient systems to harvest, Whiting said. In tests at Olsen Brothers Ranches at Prosser, Washington, the picking rate on fifth-leaf Tieton UFO-trained trees on Gisela 5 rootstocks was 30 to 35 percent faster than in a central leader block in the same orchard, using the same crew. The UFO block had a crop of 11.4 tons per acre versus 7.1 tons per acre in the central leader.
Eleven of the 12 pickers in the Olsen crew preferred working with the UFO trees. The other picker liked the fact that in the central leader trees he could stand under big branches and drop the fruit into the bucket, whereas the fruit on the UFO system was less visible.
2 Find the genes relating to abscission
In order for sweet cherries to be harvested mechanically, they must fall easily from the tree. The cherries are treated with Ethrel (ethephon) to loosen them from the stems, but it is helpful if they have a low pedicel-to-fruit retention force—preferably 400 grams or less, Whiting said. Geneticists at WSU are working to identify the genes involved with low pedicel-fruit retention force so that the university’s cherry breeding program can use markers to select for that characteristic when developing new varieties for mechanical harvest.
Whiting said if a grower is planting an orchard that might be mechanically harvested in the future, the retention force of the variety would be important. Bing responds well to the Ethrel treatment and the fruit loosens from the stems, whereas Chelan doesn’t respond to Ethrel. Selah naturally loosens easily from the stems.
3 Find engineering solutions to improve labor efficiency
Zhang has been developing a vibrating actuator to shake the trees to loosen the cherries. The actuator will be tested on an over-the-row system as well as on ground equipment.
Meanwhile, Picker Technologies, LLC, is working on a fruit collection and handling system for cherries and has built a prototype of a mobile harvest platform. The company intends to incorporate a system to produce ultrafine ice particles that can be sprayed onto the cherries in the bin during harvest to cool them down and plans to include in-field sorting to detect soft or bruised fruit or doubles.
4 Extend shelflife and consumer appeal
Researchers at Michigan State University’s School of Packaging are looking for novel packages that can extend the shelflife of cherries. They have been testing a clamshell pack made of polylactic acid (PLA), with and without microperforations in the lid. The package, which is compostable and recyclable, limits fruit weight loss and fungal growth.
5 Develop markets for stem-free cherries
Tests at WSU’s School of Food Science showed that consumers preferred the appearance of stemmed cherries and thought stemmed cherries were more convenient to eat than stem-free. However, there was no difference in their willingness to purchase stemmed or stem-free.
Consumers found Ethrel-treated cherries less acceptable than untreated fruit, though Whiting said he was not sure why. The test will be repeated next year.
6 Analyze the profitability of the system
WSU and Oregon State University economists are developing interactive economic models to validate the profitability and feasibility of mechanical harvesting of sweet cherries, and of partial mechanization. They are looking at how harvest technologies could impact the bottom line for small, medium, and large growers.