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PREDICTING HARVEST SIZE OF McINTOSH APPLES 

 F.W. Southwickl 



It is known that apple fruit size at harvest from healthy trees can be predicted with 

 reasonable accuracy by measuring fruit size much earlier in the growing season. 

 Therefore, measurements of fruit diameters in July or later can be used to accurately 

 estimate average fruit size of Mcintosh in early- mid- or late-September, assuming 

 severe drought conditions do not develop during July or August. By taking some early 

 size measurements a grower can determine whether or not he should consider doing 

 some hand thinning to improve the overall size of the persisting fruit at harvest. The 

 earlier hand thinning is done after completion of the June drop, the greater the 

 improvement in size of the persisting fruit and the smaller the decrease in total yield. 



Data in Table 1 can serve as a guide, showing the approximate harvest size of Mcintosh 

 on September 15 when fruit diameters were measured on July 15 and August 1. It is 

 assumed that the Mcintosh were sprayed with Alar-85 in mid-July at a concentration 

 of 1000 ppm for pre-harvest drop control. To determine average fruit size, measure 

 at least 25 fruits a random on several trees in each block. A suitable measuring device 

 for measuring fruit diameters (Cranston Calpher) can be purchased from the McCormack 

 Fruit Tree Co., Inc., 611-A Englewood, Yakima, Washington 98908. 



Table 1. Prediction of fruit diameter (inches) of Mcintosh apples on September 15, 

 based on size on July 15 or August 1. 



Professor Emeritus, Department of Plant and Soil Sciences 



