USE OF ETHEPHON TO PROMOTE RED COLOR AND RIPENING
Ethephon, sold as Ethrel and Cepha, releases ethylene, a natural growth regulator. Ethylene stimulates ripening in fruits that have reached a certain minimum stage of maturity. Several changes accompany ripening of apples, including the following: They become softer; an abscission zone develops between fruit stem and spur; starch in the fruit is converted to sugars; internal production of ethylene increases; and the rate of respiratory heat production increases. In McIntosh and some other cultivars, the ability to develop red color in the fruit skin is stimulated as a ripening response. Use of ethephon will advance development of all the maturity-dependent changes.
Stimulated ripening may be desirable where fruit is needed for early fresh market, for increasing the sweetness of early cider, or for getting an early start on harvesting a large crop. In summer cultivars it may be possible to harvest in one picking rather than 2 or 3.
McIntosh that are treated with ethephon 2-3 weeks prior to normal first harvest can be ready to pick within 5-12 days after treatment. However, fruits that are ripened and picked more than about 1 week before normal are often inferior in quality and size compared to full-term fruits. The speed with which treated fruits ripen is influenced by the rate of ethephon applied, the nearness to normal ripening, the temperature during and after application, and the cultivar. High temperatures hasten all ripening responses except red color development. Serious losses have resulted in some instances where growers did not anticipate the potential problems. Treat only small amounts of any cultivar until you have experience with managing the harvest and the marketing of that cultivar. Inspect treated fruit daily for maturity (firmness) on the tree, and frequently after harvest. Move harvested fruit quickly into cold storage, market, or cider.
Uniform within-tree response to ethephon (and other growth regulator sprays) is rarely possible with concentrated, low-volume sprays. Response of each fruit is related to the amount of ethephon deposited on that fruit's spur leaves, and other very nearby leaves. Therefore, dilute application is recommended, spraying to completely wet all fruited areas.
DOSAGES. Where stimulated ripening is desired, the following ethephon rate choices are suggested:
• Use 1/3 to 2/3 pint per 100 gals. for summer cultivars that will be stored for no longer than 2 weeks. Apply within 4-10 days before normal first harvest.
• Use 1/3 to 2/3 pint per 100 gals. for McIntosh that will be held at 32oF for up to one month. Apply within 4-12 days before normal first picking.
• Use 1/4 to 1/2 pint per 100 gals. for McIntosh that will be held at 32oF until January 1. Apply 5-10 days before normal first picking. Ethephon-treated fruits intended for storage at 32oF for sale in November and December must be harvested quickly and cooled to storage temperature as soon as possible. Any delay in harvest or immediate cooling will result in fruit much too soft for these later sales.
The restricted entry interval for ethephon is 48 hours with written worker notification required. The preharvest interval is 7 days.
NAA for Ethephon Treatments. To delay fruit drop, naphthaleneacetic acid (NAA), 10-20 ppm can be included in the ethephon tank mix. The restricted entry interval and preharvest interval for NAA products are: 24 hour REI and 2 day PHI for K-Salt Fruit Fix; 48 hour REI and 5 day PHI for Fruitone-N.