Fruit Detachment Force of Southern Highbush Blueberry: An Aid to Selection of Cultivars Suitable for Mechanical Harvest

Blueberry (Vaccinium spp. ) acreage has expanded significantly in the last decade in the southeastern region of the U.S. and the value of Florida’s fresh-market blueberry industry has steadily increased to $73 million in 2009, up 87% from the 2007 season. Many new plantings are being established and this trend will likely continue for the near future. A number of factors have contributed to this trend; among them are the availability of commercial southern highbush cultivars from the University of Florida (UF) breeding program and the availability of dormancy-breaking chemicals. With these, growers from southern Georgia to southern Florida can harvest in the high-value market window of mid-April to mid-May. Currently, fresh-market blueberries are hand harvested in Florida at an estimated cost of $1.54/kg. However, mechanically harvested blueberries could lower harvest costs to <$0.22/kg, reducing harvest costs statewide by >$4 million. Blueberries mature at different times on the same plant, necessitating multiple harvests, and one factor affecting the adoption of mechanical harvest is fruit detachment force (FDF). Ideally, blueberries that are immature (green stage) or unripe (red stage) would have a higher FDF than those that are ripe (blue stage), enabling selective, multiple harvests. In May 2009 FDF was determined on full-sized green, red and blue fruit considered as having potential for mechanical harvest: three commercial cultivars (‘Sweetcrisp’, ‘Star’, and ‘Farthing’) and seven UF breeding lines (01-173, 06-465, 06-556, 06-553, 06-571, 06-80, 06-83). Individual fruit were detached (15 to 20/color stage) using a handheld, digital force gauge fitted with a dual wire, curved probe. For each reading, the stem adjacent to the pedicel was secured with one hand and the probe was inserted on either side of the fruit pedicel to contact the stem-end of the fruit. The gauge was then pulled out with uniform motion and maximum FDF was recorded upon fruit detachment. Green fruit required more FDF (1.8 to 3.5 N) than blue fruit (0.7 to 1.5 N) for all but ‘Sweetcrisp’. FDF for red fruit from lines 06-465 and 06-80 was lower than green fruit, but only the former was higher than blue fruit. These results indicate that green fruit from most of these cultivars/lines would not be removed from the bush with a properly adjusted mechanical harvester and that breeding line 06-465 shows potential for selective harvest of blue fruit.