1918] 



HOETICULTURE. 243 



formation of fruit buds, proper irrigation systems to produce apples of best 

 keeping quality, the best irrigation scheme for the production of relatively 

 large amounts of extra fancy and fancy fruits, and the influence of soil moisture 

 upon the health of the tree as indicated by winter injury and blight. The re- 

 sults of the experiments are presented in a series of tables and charts and 

 fully discussed. The investigation as a whole is summarized as follows: 



"The trunk of an apple tree makes its growth during the first part of the 

 growing reason. By August 1, 75 per cent of the total season's growth is com- 

 pleted. A cover crop greatly checks the rate of growth of the trunk. The 

 trunk growth of Jonathan apple trees is directly affected by the amount of 

 irrigation water applied during the first part of the growing season and by the 

 percentage of water in the soil the preceding dormant season (winter). The 

 latter factor may easily overbalance in its effect the former one. 



" The terminal (limb) growth of Jonathan apple trees is practically completed 

 by the first part of July. No growth is made after July 15. Irrigation after 

 this date has no effect on the wood growth of the tree. As a general rule, the 

 more irrigation water applied before July 1, the greater the terminal growth 

 although the percentage of moisture in the soil the preceding fall and winter 

 probably affects the terminal limb growth. A cover crop in an orchard greatly 

 checks the limb growth of the trees. 



" Jonathan apples grow very slowly from the time they are formed until about 

 July 15, completing less than 30 per cent of their total growth during the first 

 half of the total period they hang on the trees. Irrigation during this period 

 (before July 15) will not increase the size of the apples. Jonathan apples 

 grow most rapidly during the period starting about July 15 and ending about 

 two weeks before picking time, when the rate of growth becomes considerably 

 slower. Irrigation during this period of rapid growth has a very decided 

 effect in increasing the size of the apples although it has practically no effect 

 on the wood growth of the tree. 



" Heavy irrigations in the spring tend to increase the wood growth of an 

 apple tree and this tends to increase fire blight. A cover crop, preferably 

 alfalfa, greatly decreases the wood growth and so lessens the amount of blight. 



"Winter injury to apple trees, especially young trees, is usually the result 

 of the wood of the tree not being thoroughly ripened or due to the ground being 

 too dry during the winter. It is advisable to hold the water off during the 

 latter part of the summer and let the wood ripen ; then, if the fall is excessively 

 dry, to apply a late dormant irrigation just before the ground freezes. Chlo- 

 rosis or bunches of white leaves on apple trees is often a sign of overirrigation. 



" Where two plats were given an equal total amount of water for the season, 

 one early during the vegetative period of the tree and the other later during 

 the fruit developing season, the last mentioned system invariably produced 

 much the larger apples. Plats irrigated heavily early in the season produced 

 heavy foliage which was detrimental to the development of color on the apples, 

 riats which were not forced to excessive leaf and wood growth during the 

 vegetative period by early irrigation gave better color to the apples when 

 given liberal applications of water during the period of most rapid apple 

 growth. This experiment shows that fruit growers may, by irrigation, very 

 materially augment color in fruit production if the water is applied at the 

 right time. The plat which was given little irrigation early in the season 

 (before July) and liberal applications during the period of most rapid apple 

 growth (from July until two weeks before picking time) gave the highest per- 

 centage of extra fancy and fancy grades and aLso fruit of the best storage 

 qualities. This plat (at Twin Falls, Idaho) with a dense clover cover crop 

 was given a little over 2-acre feet of water during the entire sea.son. An even 



