Stone fruit thinning spray could offer growers a helping hand

Tender fruit growers learned of a new option for thinning peaches and plums coming to Canada that could reduce labour pressures and improve fruit quality. ~ Farmphotos.ca photo

By Luke Edwards

Use of an amino acid that’s already naturally occurring in fruit trees could help tender fruit farmers offset rising labour costs associated with hand thinning.

Attendees to the Ontario Tender Fruit Growers annual general meeting last month in Niagara-on-the-Lake learned about research into how 1-aminocyclopropanecarboxylic acid (ACC) could reduce the need to hand thin peach and plum trees by as much as 50 per cent. It’s a process already used with apple trees in Canada and stone fruit south of the border. With labour costs rising and availability dropping, John Cline said there’s some optimism around a product called Accede that has ACC as its active ingredient.

“Right now hand thinning is really the only option for thinning peaches,” said the professor of pomology and tree fruit physiology at the University of Guelph. Cline was a guest speaker at the March 26 tender fruit growers AGM.

In addition to offering relief for labour needs, Cline said research suggests the product could also improve other aspects, namely by offering earlier thinning opportunities.

“If you get your fruit off earlier, (the remaining fruit) should be able to size better,” he said.

Researchers are continuing to study the product on local farms. Research began a few years ago on peach and plum orchards. It’s already been labeled for apple growers in Canada for two years, Cline said. The plan from Valent was to release it for stone fruit growers this year, but that has now been pushed back to 2027.

ACC naturally occurs in fruit trees, and seems to lead to an increase in ethylene production, which causes fruit drop. Thinning fruit trees is a key step to ensure the tree’s energy is most efficiently utilized.

The research of Cline and his team looked at several aspects and variables, including spray rate. It’s already used in the United States, where a 300 to 600 parts per million application is recommended. Cline said he and his team wanted to be more precise.

“We wanted to optimize or find the ideal rate,” he said.

For peaches, he said their research suggested a 400 to 500 ppm application, done once sometime from pink bud to petal fall.

For plums, the rates were a little lower, to a maximum of 450 ppm. However, it can be applied on fruit up to 10 mm.

There were some issues with the product, though, Cline said, that could affect Canadian growers. They’ve tested the product over multiple years, and while in some years on some varieties they were able to approach the target of reducing hand thinning by 50 per cent, in other instances the impacts were more negligible.

The culprit, as is often the case in this part of the world, was Mother Nature.

“It’s likely much related to the weather,” he said.

It seems cooler temperatures can have a negative impact on effectiveness, so Cline cautioned growers to be careful if they choose to employ the spray when it becomes available.

The product can also cause leaf yellowing or leaf drop, though Cline said it seems the trees recover within a month or so.

Some research Cline has come across suggests the pedicel, which is the stalk that attaches to the flower, is the mode of action. This produces an added challenge, Cline said, as it’s a small target to reach, especially for peach trees.

The product is registered. More study on the product will be taking place in 2026.