Issue link: https://read.dmtmag.com/i/616629
24 JANUARY 1, 2016 GOOD FRUIT GROWER www.goodfruit.com P lant growth regulators are useful tools to manipulate fruit trees and help make an orchard more productive, though they can't work miracles, Dr. Duane Greene, horticulturist at the University of Massachusetts, told Washington growers at a recent fruit school. It has to start with a well managed orchard, he said. "They do not undo a multitude of sins. They are not miracle workers. You can't transform poor quality fruit on poorly managed trees into good quality fruit." Plant growth regulators have many uses, but in his presentation at Washington State University's Fruit School on Apple and Pear Horticulture in November, Greene focused on use of the gibberellin synthesis inhibitor prohexadi- one calcium (sold under the brand names Apogee and Kudos) to control vegetative growth. Although tree growth also can be controlled by rootstock, crop load man- agement, tree training, pruning and root pruning, use of a plant growth regulator has several advantages. It's convenient, it can be started and stopped as needed, and the effect is not irreversible. Gibberellins are a group of hormones responsible for stimulating vegetative growth, and controlling production of those hormones is a very effective way to regulate tree growth, Greene said. There are several known gibberellin biosynthe- sis inhibitors, but prohexadione calcium is the only one approved for use in U.S. apple orchards. The compound is relatively benign, Greene said, and its registration was fast-tracked in the late 1990s. Besides controlling vegetative growth to enhance productivity, it is used in eastern U.S. growing regions as an alternative to streptomycin applications for controlling the shoot phase of fire blight. Two formulations are available in the United States. Apogee has been available since the compound was registered and is the one most widely used. However, Greene said there is still much to learn so that growers can take full advantage of it. Kudos was registered more recently. Both contain 27.5 percent active ingredient and have performed similarly in trials. In other parts of the world, prohexa- dione calcium is available under the brand name Regalis, which contains only 10 percent active ingredient but also includes magnesium sulfate in the formulation. Keys to success For the best results, growers should include either an equal quantity of mag- nesium sulfate or water conditioner with the Apogee to lower the pH level. At high pH levels, Apogee becomes inactive. A surfactant should also be included in the tank and an anti-foam agent if the sur- factant is one that foams. Apogee should Getting the most out of APOGEE Growth regulator should be applied as early in the season as possible. by Geraldine Warner "If you don't get it on early, you're going to lose a real opportunity." —Duane Greene S everal plant growth regulators are available for enhancing the quality of apples at harvest or for managing harvest maturity. Dr. Dana Faubion with AgroFresh, a major supplier of 1-MCP for the tree fruit industry, said 138 growth regulator products are registered for use on apples in Washington, of which about 23 affect fruit quality. Plant growth regulators fall into five classes of hormones: auxins, cyto- kinins, ethylene, anti-ethylene products and gibberellins. A hormone is a chemical messenger that sets a process in motion within the plant. NAA (naphthaleneacetic acid), sold by Amvac under the brand name Fruitone L, is an auxin that prevents fruit drop by inhibiting abscission. It can be applied between four weeks and one week before expected har- vest and is effective for two weeks. It has a two-day preharvest interval. A challenge of using this material is that high levels can accelerate fruit senescence and its effects can vary depending on the rate, timing and condition of the fruit. Promalin is a mixture of two growth regulators: gibberellic acid 4 and 7 (GA) and the cytokinin benzyladenine (BA). It is applied around bloom to enhance fruit size and typiness. Ethrel (ethephon) is a synthetic version of the ripening hormone eth- ylene. It can be applied before harvest to improve the red color of apples and degreen the fruit. However, this is a tricky chemical to use, Faubion warned, as it stimulates fruit respiration and production of ethylene inside the fruit and can make the apples turn greasy and soft, impairing storability. AVG (aminoethoxyvinylglycine), sold by Valent under the brand name ReTain, inhibits production of ethylene in the fruit to prevent fruit drop Enhancing fruit QUALITY Many growth regulators are available for apples. by Geraldine Warner