The majority of horticultural writers seem to favor the summer pruning of apple trees. The practice, and the arguments made in its favor vary widely and in some instances seem almost contradictory. On the other hand some experimenters and practical workers have obtained negative results by summer pruning from the view-point of crop production and tree growth. Dickens(1) caused unproductive ten year old apple trees in Kansas to bear satisfactorily during the fourth year of summer pruning. The Gardners' Chronicle(2) compiled the opinions of more than one hundrend eighty-five fruit growers who practiced summer pruning, and about 82% of these orchardists reported satisfactory results while the remainder expressed doubts as to the value of the practice. Opinions compiled from English fruit growers by the Journal of Royal Horticulture Society(3) (1908) showed that the consensus of opinion was uncertain as to the effects of summer pruning and that much depended upon soil, climate, varieties and season of practice. Drinkard(4) checked wood growth and greatly stimulated the formation of fruit buds by summer pruning but one year.
Batchelor, L. D. and Goodspeed, W. E., "Bulletin No. 140 - The Summer Pruning of a Young Bearing Apple Orchard" (1915). UAES Bulletins. Paper 91.