Growth Regulators to Aid in Apple Tree Training and Growth Control

Increasing branching

Most training systems rely on developing 3 to 5 main branches close to the ground and then second and/or third layers that parallel the bottom branches. The trees you receive from a nursery may not have enough branches, or branches may not be located at the proper place on the tree. The traditional way to fix this problem is to severely head the tree back and try to force new branches to arise at desirable locations. On small-caliper trees this method often works well, but on larger-caliper trees (5/8 inch and up), forcing branches on the trunk is very difficult.

Using a growth regulator composed of cytokinins and gibberellic acid (BA+GA) such as Promalin, Perlan, or Typy in such cases can help stimulate additional branches to grow. Foliar applications should be made when new shoot growth is approximately 1 to 3 inches long, approximately 2 to 4 weeks after bloom. Apply 125 to 500 ppm (0.25 to 1.0 pt/5 gal) of spray mixture. Thoroughly soak the area of the tree where you want buds to break. A buffering agent (e.g., buffer X) or nonionic wetting agent (e.g., Tween 20 or Triton X-100) should be added to the tank at a rate of 0.2 to 0.3 percent (1 to 2 oz/5 gal) before adding BA+GA. The final spray solution should have a pH no greater than 8.

Thoroughly wet the foliage and bark of trees to be treated. Five to 10 gallons of spray mixture applied with a pressurized hand sprayer will treat 200 to 300 nonbearing trees 1 to 4 years old.

BA+GA may also be mixed with latex paint and applied directly to buds. Apply in the spring when terminal buds begin to swell, but before shoots emerge. DO NOT apply after buds break. Applications made after buds have broken may cause injury to tender shoot tips and fail to promote shoot growth from that point. The application rate is 5,000 to 7,500 ppm (0.2 to 0.33 pt/pt of latex paint). Add a buffering agent or a nonionic wetting agent to the latex paint at a rate of 0.5 to 1.0 percent (0.1 to 0.15 oz/pt of paint) before adding BA+GA. The wetting agent improves the dispersion of BA+GA in the latex paint; it also improves wetting and absorption through the waxy layer of the bark.

Uniformly apply the BA+GA-latex paint mixture with a brush or sponge and thoroughly cover the bark surface. NOTE: Apply only to one-year-old wood (see Table 1-17).