Always capricious but, in the mood, Mother Nature can also be quite forgiving. Consider tender fruit. Just 15 per cent of an orchard’s blooms need to be pollinated for yield to be profitable.

This means that either the blossoms or the developing fruit need to be thinned. Apple and pear growers have access to chemical thinners to help manage crop loads to ensure good fruit sizing and quality while peach growers are restricted to thinning fruit by hand. And topping out at more than $1013/ acre, the long- held practice currently results in a peach production expense ranking second only to harvest labour costs.

This recent metric from the Ontario Ministry of Agriculture, Food and Rural Affairs (OMFARA) provides a timely focus on new technologies targeted at helping to reduce labour costs.  One such product is Accede, a new plant growth regulator (PGR) from Valent BioSciences, and the first chemical thinner registered in the United States for use on peaches and nectarines. Its active ingredient, ACC, encourages the plant to produce ethylene, a gas acting as a naturally occurring plant hormone to regulate fruit drop, colouring, and ripening. The product is already registered for use in Canadian apples. Depending on approval of Valent’s application to the regulators, the technology could be available to tender fruit growers as a minor use extension to the label in as little as a couple of years.

University of Guelph pomology professor John Cline has hands-on experience with Accede, having just completed six trial growing seasons using the product’s soluble granular formulation. This project gained more hands on deck in 2022 with Kathryn Carter, an OMAFRA fruit crop specialist, and in 2023 with Sofia Franzluebbers, an MSc candidate at Guelph.

The Canadian team has been encouraged by previous trials in the U.S. where Accede was shown to reduce peach fruit set by an average of 40 per cent and nectarine fruit set by an average of 25 per cent. When sharing these results at a product webinar in November 2023, Valent BioSciences noted that ACC can be applied from pink bud to petal fall to achieve these results.

“The earlier the thinning, the better effect on size because you’re not wasting carbohydrates of the tree,” said Jozsef Rocsko, senior product development manager, Valent BioSciences. This points to chemical thinners possibly becoming a valuable tool to help overcome poor sizing for early-season peach varieties.

As for labour benefits, Anna Wallis, IPM co-ordinator for fruit at Cornell University, noted, “A first application of Accede in peaches at 20 per cent bloom and a second application at 100 percent bloom can result in a significant reduction in fruit, cutting follow-up hand thinning almost by half. And using ACC can decrease the number of picks for some peach varieties, resulting in additional labour efficiencies.” 

While Accede is a soft or biopreferred chemistry, it should be used judiciously. Cold temperatures appear to amplify the effect of the ACC active ingredient, and growers should always apply the product conservatively, according to variety.

Todd Burkdoll from Valent BioSciences was involved with trials in California’s Central Valley in 2017. At that time, there was no label for post petal fall. After that point, applications were observed to cause leaf drop.

“Coverage, concentration and timing are critical,” says Burkdoll. “Do not go over 600 ppm. Growers need to observe open flowers for peak effectiveness.”

John Cranmer, a 25-year veteran employee at Valent BioSciences advises growers to go slow. “Treat one row first at a rate of 300 ppm. PGRs work best under slow drying conditions. If temperatures warm up quickly, the product will have less efficacy, and the product needs eight hours of a rain-free period.”

A key learning has been not to mix Accede PGR with Fontelis fungicide. A re-entry period of 12 hours is needed. Another learning: set up the sprayer correctly for uniform coverage. Proper application of product to the upper canopy results in better thinning. All that said, growers will need to see how the product works on different peach cultivars.

Reporting on Ontario trials, Cline has collected data from the Simcoe Research Station as well as commercial orchards in the Vineland area. Despite Accede already being registered in Canada for apple thinning, trials on peaches and nectarines are needed to support a User Requested Minor Use Label Extension (URMULE).

Trial participants including David Hipple, Beamsville, are hopeful the product becomes a labour-saving tool. “My potential use may be dependent on the season,” says Hipple. “Weather plays a role.”

In Cline’s experience, the best timing for spraying is between pink bud and full bloom.  Faced with the risk of frost, the recommended approach is to lower the application rate.

“We’ve also noticed that if there’s winter injury and a low flower count, then it’s best not to over-thin,” says Cline. “On the plus side, we’ve noticed that the product works well at temperatures as low as 2°C. When temperatures are less than 5°C, lower rates are required to prevent overthinning.”

Trial work started in 2023 on both Japanese yellow and European blue plums. A principal objective of PGR use is for crop load management but the end benefit is to help size fruit.

“When the product is used at optimal concentrations to thin plums, there may be an increase of 10-15 per cent in fruit size,” says Cline. “For growers, the question will be deciding where the cost benefit is in reducing labour or in increasing fruit size, or both.”

Cline has funding for four trials in 2024, two with plums and two more with peaches. Funding for the trials comes from the University of Guelph Agri-Food Innovation Alliance program, OMAFRA, Ontario Tender Fruit Growers, the Niagara Peninsula Fruit and Vegetable Growers’ Association, BC Fruit Growers’ Association and Valent BioSciences. Specific funding from NSERC is targeted at understanding how the product works in the plant.

New technology claiming to reduce farm labour costs is often like the Holy Grail, long sought but never seen. Canadian growers are waiting to see if PGRs can make a difference on 8,600 acres of peaches, nectarines, and plums across the country.