Nurseries working to provide apple growers with the well-branched, “feathered” trees they want to plant can use the chemical MaxCel and will find it as effective and safer than Tiberon in inducing branching.

That’s the good news coming from Cornell University researchers and nurseries that have worked with them. They were all surprised last year by news that Tiberon, first used in 2009 to increase branching on nursery stock, would no longer be available after 2012.

New research shows that MaxCel works effectively, and does it without having the stunting effect on trees that Tiberon sometimes showed, especially on some varieties grown by nurseries in the eastern United States. Nurseries in the West did not see the stunting of tree growth and were more satisfied with Tiberon. It does take more applications of MaxCel to achieve the effect than it does with Tiberon.

The research was conducted by Dr. Terence Robinson, Cornell University horticulturist in Geneva, New York, and Mario Miranda Sazo, who is with Cornell Cooperative Extension in the Lake Ontario Fruit Program in Newark, New York. The research was done in 2010, 2011, and 2012 comparing three growth regulators—Promalin (a mixture of cytokinin and two gibberellins), MaxCel (the cytokinin benzyladenine), and Tiberon (cyclanilide). MaxCel is a product of Valent Agricultural Products and is used in thinning apples and pears. Tiberon is ­manufactured by Bayer Environmental Science.

The researchers’ work in 2010, done only in western New York, made them wary of Tiberon because it reduced terminal growth on trees, especially of the Macoun variety.  Growers who are using the tall spindle orchard system want trees to reach the 10-foot trellis wire in two years, and stunting the trees in the nursery didn’t seem like a good idea. While each of the four tested varieties—Gala, Acey Mac, Macoun, and Empire—showed some reduction in terminal growth rate after application of Tiberon, Macoun’s growth rate never recovered as the others did, the researchers said.

“Over the course of the eight weeks of measurements, Macoun appeared to be the most sensitive cultivar to higher rates or multiple sprays of low rates of Tiberon, followed by Acey Mac a bit less sensitive, followed by Empire, and then Gala, which was the least sensitive and had the quickest recovery in shoot growth rate following Tiberon treatment,” they reported.

Inducing branches

“Our results in 2010 with MaxCel have shown that three applications of 500 parts per million have given very good branching with most cultivars in New York,” they said.

With Tiberon, one or two sprays totaling about 100 ppm induced feathering. “Both MaxCel and Tiberon were very effective in inducing branching on the four varieties we tested,” they said.

In 2011, they tested lower rates of Tiberon and multiple doses of low rates, which gave less stunting, but tree height was still reduced compared to the MaxCel-treated trees.

“Lateral branching or feathering of nursery trees is controlled by apical dominance within the stem of the tree wherein the terminal bud of a nursery apple tree exerts control over the development of the lateral buds,” the scientists explained in a report in New York Fruit Quarterly in 2011.

“The young leaves in the apical bud produce a hormone called auxin that diffuses downward and inhibits the development of lateral buds lower down on the stem. Therefore, to produce a well-branched, highly marketable tree, apical dominance must be interrupted. Traditionally, nurserymen have accomplished this through the removal of small, undeveloped leaves, in a process called pinching or plucking.”

This traditional method is labor-intensive and led to initial work to find chemical methods to offset apical dominance and induce branch formation.

Dr. Don Elfving of Washington State University developed the use of Tiberon, which inhibits transport of auxin down the stem and allows branching of apple and cherry trees.  This led to widespread commercial use of Tiberon in 2009-2011 and the production of beautifully branched trees for several years.

However, the New York researchers observed some negative effects in the orchard where some trees were slow to begin to grow after planting. This effect was then studied in the nursery setting.

Tiberon treatment did improve branching and improved branch angles for all cultivars, and did so more than on MaxCel-treated trees. In addition, they said, many of the feathers on the Tiberon-treated trees were short, ideal for the tall spindle system.

“Flatter angles produced by Tiberon with other cultivars would be a significant advantage for the tall spindle system since less labor would be required to tie feathers or branches down after planting,” they said.

They concluded, however, “In general, MaxCel was a safer product than Tiberon under New York conditions.”

No choices

The question of which is better is somewhat moot since Tiberon will no longer be available.

Bill Howell, manager of the Northwest Nursery Improvement Institute, Prosser, Washington, holds out little hope that Bayer Corporation will change its attitude about marketing Tiberon to nurseries, which is a small use. The material is no longer patented, and Bayer manufactures the active ingredient to blend and make other products that are patented for other uses, mainly in cotton. Howell has asked Bayer to provide the active ingredient for the nursery industry. Although local Bayer representatives were sympathetic to the nurseries’ request, his letters to Bayer corporate officers have not been answered.

In 2012, the Northwest Nursery Institute partnered with Robinson and Miranda Sazo from Cornell to evaluate alternatives to Tiberon in Washington, New York, Maryland, and Ontario, Canada. The institute provided some funding to support the Cornell research, and two of its members volunteered trees, time, and workers to ­evaluate the chemicals.

In 2012, the researchers conducted branching trials comparing Tiberon, MaxCel, and Promalin, working with several nurseries, including Bill Pitts and Paul Wafler at Wafler Nursery in Wolcott, New York; Jack Snyder, Dick Snyder, and Shad Snyder at C & O Nursery in Wenatchee, Washington; and Pete Van Well, Sr., and Ric Van Well at Van Well Nursery in East Wenatchee, Washington; John Baugher at Adams County Nursery in Maryland; and Rob Haynes, Leslie Huffman, and Kathryn McFadden-Smith at Mori Nursery on Ontario, Canada.

Preliminary observations from the 2012 trials are that it took three times as many sprays with MaxCel to get the effect of one spray of Tiberon, so it means more work for the nurseries to use it. But MaxCel was effective at inducing branching at all locations. Tiberon seems to have worked better for nurseries in the West than for nurseries in the East, where the stunting effect appeared. A detailed report will be published later in the New York Fruit ­Quarterly.

MaxCel currently is labeled for use on apples for thinning, but not specifically for this use by nurseries to induce branching.  However, Valent is in the process of expanding the label of MaxCel to include the use in ­nurseries for branching.