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Anew growth regulator that nurseries can use to promote branching of young apple and cherry trees should be available for use this year.

Dr. Don Elfving, horticulturist with Washington State University in Wenatchee, said Tiberon, which contains the active ingredient cyclanilide and is produced by Bayer CropScience, received federal registration last fall. He has been testing the product since 2000.

Bayer markets a number of cyclanilide products for various crops. Elfving said the active ingredient induces branching in a large number of plants.

"It seems to work on about 50 percent of the species on which it’s tried, and it does a nice job of branching," he said.

It will promote branching on apple cultivars that don’t branch well naturally, such as Cameo, which tends to grow strongly without branching, he said. What makes cyclanilide interesting as a branching promoter is that it can induce lateral branching but doesn’t do that by damaging the central leader, Elfving said. Many of the branching agents tested in the past appear to cause some physical injury to the top growing point of the tree. Elfving said it’s not known exactly how cyclanilide works, but it is probably an auxin transport inhibitor, which temporarily reduces the apical dominance, allowing buds to begin growing. Once that happens, the buds continue to enlarge and form lateral shoots.

The product is registered only for use on nursery trees and is generally used in early summer.