EXPERIMENT STATION BULLETINS. 587 



rerliictioii of tlie tops is generally followed by an excessive production 

 of sprouts on the main branches and usually by severe sunscald of the 

 bark on the larger limbs. This practice, therefore, leads to serious 

 injury of the trees, and many orchards of the State are monuments of 

 the disastrous results often following this practice. One should not 

 attempt to change to any great degree the form of a mature tree. The 

 height of the uppermost branches of a high-topped tree may be gradu- 

 ally reduced to a moderate degree by successive light prunings over a 

 series of years, but not by removing so much growth at any one time 

 as to upset the balance of the tree or expose the remaining branches to 

 sunscald. 



TRACTICAL RULES FOR GUIDANCE. 



Mature trees should be pruned annually but moderately. 



Remove all dead branches and watersprouts except such of the latter 

 as are, desired for fruiting wood, thinning out as many of the outer 

 branches where the growth is too dense and as many of the branches 

 growing in undesirable directions as the present vigor of the tree and 

 fruiting record v/ould seem to permit without seriously disturbing its 

 equilibrium. 



It is better to increase vegetative growth by feeding, cultivation, and 

 cover-cropping than by excessive pruning. 



Make all cuts clean and close and see that all wounds have good sur- 

 face drainage. 



On trees infected with bark cankers, prune only such branches that 

 seem of most urgent necessity as each wound is apt to prove a new 

 infection point for such troubles. Disinfect the pruning tool after 

 each cut to prevent the possibility of spreading the infection by the 

 pruning tool. 



Do not jeopardize the present health and fruitfulness of high-topped 

 trees by excessive pruning to make them low and round-topped. To 

 moderately modify such high-tops requires time, patience, and skill. 



COVER CROPS. 



While it has been a general practice for a number of years to cover- 

 crop tilled orchards, the importance of efficient cover-cropping bears a 

 new significance in its value under the changed conditions of the times. 

 This is due particularly to the present reduction in the supply of stable 

 manure from the cities for orchard fertilization, and the present neces- 

 sity of increasing and maintaining the organic content of the soils to 

 increase production. 



The loss of fertility of many of the orchard soils is due largely to 

 the decrease in the amount of humus that they contain. Humus is 

 the product of the partial decay of organic matter and is considered 

 a necessary ingredient of fertile soils. Most of the nitrogen of the soil 

 is present in the more or less decomposed organic matter. Besides 

 nitrogen, this organic matter either contains phosphoric acid and 

 potash in available forms or assists in making them available from the 

 mineral elements. Under natural conditions, the humus in the soil 

 resists decay. Tillage in an orchard is therefore practiced and is 

 desirable because it hastens the decay of this potential plant food by 



