As a group of Northern California clingstone peach growers crowded around, Roger Duncan fired up a tractor-mounted string blossom thinner and started in on a row of Ross peaches in an orchard south of Modesto. Duncan, a University of California (UC) farm adviser in Stanislaus County, was clearly pumped up about the possibilities of the Darwin PT 250.
Imported from Germany, the thinner has so far shown to have a huge impact on growers’ bottom lines, said Duncan. In fact, the $16,000 unit may very well pay for itself in just one year of use, he said. What comes as a surprise to many, however, is that the thinner doesn’t just save growers money on thinning costs by reducing the amount of hand labor.
Duncan says that the greatest boon to the grower comes from an increase in gross income because of increased fruit size due to thinning earlier in the season. “The sooner you thin, the less inter-fruit competition you have,” he said. “It’s like the ‘Old Lady In The Shoe.’ If you kick kids out earlier, the remaining kids get bigger.”
For example, in one trial on Loadel and Tuolumne orchards, Duncan said the time required to hand thin was reduced by 27% and 22%, respectively, resulting in cost savings of $386 and $297 per acre. Even better, the yields were increased by 2.8 and 3.0 tons per acre, respectively, resulting in gross income gains of $997 and $954. Add it up and the growers realized net per acre income gains of $1,383 on the Loadel and $1,251 on the Tuolumne orchards.
However, it’s important to note that these impressive results came in a warm, short growing season and generally heavy sets in the test orchards — ideal for a blossom thinner. In addition, the trees were trained to a “V,” not the more traditional vase training system (like the trees in the photo). “When the trees are trained to a ‘V’ you will get a wall of flowers,” he said. “That’s what we think will work the best.”
It’s also important to note that in addition to the training system, the variety selection will have a great impact on results. Because it’s important to thin the early season varieties as early as possible to reduce competition and give the remaining fruit more time to size up, the thinner will work best on them. Growers won’t see such potentially dramatic increases in yields in the varieties harvested late in the season.
There can also be a wide variation in how the unit itself is employed. It has 24-inch rubber cords attached in columns along a 10-foot boom. You can add additional strings, and it stands to reason that the more strings you have, the more thinning you will do. In addition, the more strings you have, the fewer revolutions per minute you will need to get the same amount of thinning.
Ordinarily, growers will run the Darwin in the range of 175 to 225 rpm, moving through the orchard at about 1.5 miles per hour. Depending on the variety, the training system, the stage of bloom, as well as a host of other factors, growers will want to adjust their approach accordingly, said Maxwell Norton, who is Duncan’s UCCE counterpart in Merced County. “For instance, if the blossoms are coming off easily, you can turn it down, but if they’re not coming off as easily, you can turn it up,” he says. “You can tweak it in several different ways.”
Unfortunately, during this March demonstration, the Darwin was stuck on its maximum speed of 350 rpm. Duncan had to halt the demonstration almost immediately for fear he might do a number on grower Chuck Voss’s trees. But the growers on hand seemed undeterred by the glitch, in part because of testimonials from growers such Paul Van Konynenburg, who farms west of Modesto. Van Konynenburg said he bought a unit prior to last season, and it paid for itself in the 2010 crop year. “Now I’m doing all my Loadel and Tuolumne (blocks) with it,” he said, adding that he was doing checks on other varieties.