Tools to Control Vigor and Obtain Colour in Pink Lady® Duane W. Greene University of Massachusetts, Amherst, MA USA

The Objective The mission of the symposium is to provide information to produce highly colored and appropriately sized apples that have the excellent harvest characteristics and possess the postharvest qualities suitable for extended storage. My contribution is to show how vegetative growth control and regulation of ripening are involved in this process.

Comprehensive Approach Appropriate control of vegetative growth requires integration and effective use of many pomological techniques. Ignoring just 1 or 2 cultural factors could make it difficult, if not impossible, to harvest a high quality fruit. The majority of this talk discuss plant growth regulator use, it will only be effective if trees are maintained using appropriate techniques.

Components Crop load management Rootstock Training system Appropriate pruning Nutrition Grower growth control techniques

Crop Load Management Establishing a balance between crop load and vegetative growth is a key annual challenge Fruit are sinks for photosynthate thus diverting vigor away from a shoot. The weight of fruit also play an important role in encouraging limbs to be brought down in a more horizontal direction thus reducing vigor. There are fruit quality problems associated with very heavy as well as light fruit set.

Rootstock Selection The degree of vigor in a tree can be predetermined by your selection of a rootstock that is compatible with your training system, soil vigor and tree spacing.

Training System Training systems are selected for a number of reasons: –In many environments there is a balance between light penetration and the need to protect fruit from sunburn. –Weather and location influence when it is necessary to make the initial growth regulator applications. –Labor inputs

PGRs to Control Growth Prohexadione-calcium (Pro-Ca) Ethephon NAA Other GA synthesis inhibitors

Prohexadione-calcium Regalis –10% active –Formulations sold in many countries Apogee and Kudos –27.5% –Formulations sold in the US and Canada places.

Keys to Successful Use Apogee and Kudos –High water pH and especially calcium can cause a significant reduction in response –A water condition or addition of ammonium sulfate using the weight of the Pro-Ca you put in the spray tank is recommended. –A surfactant –Perhaps an antifoam agent –No calcium containing compounds in the tank –A calcium residue on the leaf may affect response

Keys to Successful Use Regalis –Sufficient ammonium sulfate is already in the formulations so no additional water conditioning additive is necessary. Surfactant Defoamer if necessary

Time of Application The timing of the first application is important especially in areas where early shoot growth is common. –Sufficient leaf area to absorb Pro-Ca In areas where growth occurs over a long growing season early application is not critical. –5 to 10 cm of growth

Influence of location on growth rate and duration- Unrath

Time required for Prohexadione- calcium to achieve growth control

How Much Growth Control? Sunburn Poor Color

How Much Growth Control? The amount of growth control is determined by many factors: –When the sprays are initially applied –The amount of ProCa applied –The climate and length of growing season –Number of applications –Inherent vigor of the trees- rootstock, cultivar, soil, irrigation etc.

Terminal Growth

Side effects of the use of Prohexadione-calcium Increase in fruit set Reduction in June drop Increased difficulty in thinning adequately Possible reduction in return bloom (as a result of increased fruit set)

Influence of Prohexadione-calcium on fruit set and return bloom of McIntosh apples TreatmentFruit setReturn bloom (Mg/L)Fruit/ cm LCSABloom/cm LCSA Significance *** ***

Increase in Fruit Set

Increase in Red Color One of the challenges of growing apples in a warm climate is achieving good red color. Red color is caused primarily by anthocyanins and there are two main factors that influence this: –Light –Cool night temperatures

Increase in Red Color A primary goal of growth control is to increase red color by allowing good light penetration. Reducing shading is critical. In addition to culture and using growth retardants there are other options.

Reflective Films- Extenday

Regulation of Ripening Ethylene plays a key role in directing the ripening process in apples. Preharvest application of ethylene inhibitors are intended to delay ripening and allow the fruit to improve quality while delaying the ripening process. This is complex since ethylene production may be delayed while other parameters associated with ripening may continue to develop and advance.

Ethylene Inhibitors ReTain –This is an ethylene biosynthesis inhibitor –If ethylene is present around the fruit it has little effect on delaying ripening. –This is the prominent inhibitor used in the industry Harvista –This is an ethylene action inhibitor –It acts quite rapidly –Spray application is more difficult because is a gas and special application techniques must be used.

ReTain The degree to which ripening is delayed depends upon the time of initial application and the amount applied. –Early application (4-5 weeks before harvest) delays ripening more than if applied 2-3 weeks before harvest –Typically we apply about 830 g/ha for most varieties but with low ethylene producing cultivars we recommend ½ to1/3 that amount. Red color development is delayed and the extent of the reduction is cultivar dependent

ReTain Our goal in the Northeast US is to delay ripening and drop and allow fruit to increase in size, improve in red color and soluble solids. Ripening and fruit maturity are not stopped just delayed compared to untreated fruit. This delay allows color and soluble solids to increase under more favorable environmental conditions.

Influence of ReTain on ethylene production in McIntosh apples

Influence of ReTain on red color development in McIntosh apples

Influence of ReTain on starch rating of McIntosh apples

Influence of ReTain on flesh firmness of McIntosh apples

Harvista Frequently applied within 2 weeks of harvest A noticeable delay in ripening at harvest not always documented even when applied close to harvest SmartFresh is a better option to improve fruit quality in storage. If applied earlier it may be necessary to make another application.

Conclusion Prohexadione-calcium is an important orchard tool to improve fruit quality at harvest, primarily by controlling growth and improving light penetration. To be most effective it must be used on trees that are managed in conjunction with orchard management practices that help control growth and provide and appropriate amount of light into the canopy of the tree.

Conclusion ReTain and Harvista have been used to help fruit ripening in the orchard. ReTain has been used very effectively in the NE US and elsewhere to delay ripening and prevent preharvest drop which allows fruit to remain on the tree to develop good internal quality while increasing surface red color.