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The majority of the Mac harvest is complete as of this week. Only McIntosh treated with ReTain remains suitable for CA storage at this point -- all other Mac fruit should be marketed ASAP with SI values averaging 6 or above. Fruit drop has been minimal, particularly under ReTain treated trees. Cool nights, mild days, and lack of rain and wind has made for the good harvest conditions.
With the Mac harvest nearly complete, the effort turns to Cortland, Macoun, Empire, and Delicious (roughly in that order). Certainly market demand for Cortland and Macoun means these fruit will be picked ASAP, and maturity indexes are advancing for these varieties. Empire and Delicious are moving along -- by late in the week or during next week they will be ready for harvest.
To help determine scald susceptibility and the need for pre-storage DPA treatment of Delicious apples, UMass researchers developed a model to predict the incidence of scald development based on harvest date, the number of days when the temperature is less than 50 degrees F., and starch index at harvest (Fruit Notes, Volume 63, Number 3, Summer 1998). An on-line calculator to predict Delicious scald susceptibility has been added to the UMass Fruit Advisor (). To use the calculator, you need to input harvest date, number of days less than 50 F., and starch index (SI) at harvest. Then, it will calculate a scald susceptibility INDEX, which is used to fine tune the need for DPA treatment and rate when storing Delicious apples. Using current information from the UMass HRC (Harvest Date = Sept. 26, number days less than 50 F. (from August 1) = 15 (data from WatchDog Data Logger, ), and SI = 2.5, the calculator predicted that more than 60% of Delicious fruit would be likely to scald during storage when harvested on this date. Therefore, pre-
storage treatment with DPA at 2000 ppm is advised. Note, however, that Dr. Greene's recommendation (see his report below) is to wait another week for Delicious harvest.
Weather favorable for red color development and maturation of fruit continues. Preharvest drop on ReTain-treated blocks of McIntosh remains good. However, harvest of these treated blocks should be done this coming week. Starch iodine values on September 25 for blocks of Macoun, Cortland and Empire that did not received ReTain ranged between 3.5 and 4.0, which is very close to what one would expect for this date. Harvest of these varieties, especially those fruit destined for CA storage, should begin within the week. Start of the harvest of Delicious should be delayed for another week.
Deerfield
Cortland 3.2
Macoun 4.0
Empire 3.8
Delicious 3.0
Liberty 3.2
Shelburne
McIntosh (ReTain) 5.5
Honeycrisp 6.5
Delicious 2.2
Golden Delicious 3.4
Belchertown
Cortland 3.0
Macoun 3.5
Empire 3.5
Delicious 2.5
Healthy Fruit is written by Dan Cooley, Ron Prokopy, Jon Clements, Starker Wright, Arthur Tuttle, Wes Autio, Bill Coli, and Duane Greene except where other contributors are noted. Publication is funded in part by the UMass Extension Agroecology Program, grower subscriptions, and the University of Massachusetts IPM Program. A text version can be e-mailed to you if you contact Doreen York. Please cite this source if reprinting information.
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