Gibberellic acid on cherries
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
Cherries have natural tendency to produce “blind wood.” This phenomenon is associated with the flower bud formation on the young wood, so after the harvest we are left with long bear spots with no spurs. Research done by MSU’s Dr. John Bukovac, showed that it is possible to manipulate the flower bud formation in favor of spur development by applying gibberellic acid.
When do we apply gibberellic acid?
If you used to go by the calendar, the general recommendation is to apply the spray three to four weeks after full bloom. Perhaps, a more accurate timing would be when you have five to seven fully developed leaves on terminal growth.
Gibberellic acid (GA) will induce spur development, thus reduce “blind wood” formation and provide greater bearing capacity. How much gibberellic acid you need to a use will be the function of the tree vigor. High vigor requires a low rate; low vigor demands higher rate.
Material: Pro - Gibb 4% - commercial form of gibberellic acid.
Rate: General recommendation is 10 - 25 ppm.
10 ppm = 4 oz. / 100 gallons of water
15 ppm = 6 oz. / 100 gallons of water
20 ppm = 8 oz. / 100 gallons of water
25 ppm = 10 oz./ 100 gallons of water
How to apply
Gibberellic acid should be applied in 50-150 gallons in water. For best results, apply gibberellic acid when the temperature is 70ºF or above. At lower temperatures, the uptake has not been adequate, and the applications were less successful.
Dr. Bukovac has found that use of surfactants can yield various results; it shows no effect to some effect to over-response with phytotoxicity. Silicon-based surfactant caused phytotoxicity. In conclusion, do not use surfactants!
Young, non-bearing trees
In the environment where the trees are mechanically harvested, it is particularly important to insure good vegetative growth in the first few years following planting. Well-developed trees with a strong framework, will be able to provide uniform and plentiful bearing capacity. That is why the trees are not allowed to produce fruit in the first five to seven. By spraying gibberellic acid in high concentration (100 ppm or 40oz in 100 gallons of water) over the given span of years, there are very few flower buds, with most of the buds being converted into vegetative buds clustered in spurs along the shoots.
Timing of the application on the young trees, is the same as for the mature trees. The difference is in the concentration of gibberellic acid applied. To insure almost no flowers, use 100 ppm or 40 oz. of Pro - Gibb 4 percent in 100 gallons of water. If tree vigor is low, a second application, three weeks following the first one, may be helpful. Two applications of 50 ppm about two weeks apart are more effective than one application of 100 ppm. Do not treat more than twice in one year.
Bringing young trees into bearing
Following the early years of high concentration sprays of gibberellic acid, it is essential to bring trees into full bearing, gradually. If the plan calls for getting the trees into bearing in the eighth year after planting, in the fifth year concentration of gibberellic acid sprays should drop from 100 ppm to 75 ppm, in the sixth year there is a need for further concentration reduction to 50 ppm, in the seventh year concentration is down to 30 ppm. After this gradual “introduction” into production, the program for gibberellic acid should follow the outline proposed for trees in full production.
Following this protocol, trees are allowed to produce in increments that are higher from year to year. As the concentration of gibberellic acid decreases, the yield increases. If the concentration of gibberellic acid is allowed to suddenly drop from 100 ppm to 25 ppm or 15 ppm, that would lead to fruit oversetting, overcropping and stunting the growth.
Application timing is the same as for the mature trees: once there are five to seven fully expended leaves on terminal growth.
Caution: Do not spray gibberellic acid on the trees in the year of planting!