CITEUS DISEASES. 91 



eases, single trees are free of disease, nothing will be accomplished 

 by their destruction. The same recommendation will apply to other 

 types of citrus grown as isolated specimens for home use of the fruit, 

 or for the seed — destroy only when they become diseased. 



The destruction of the lemon or sour-orange root sprouts, so com- 

 mon and so generally scab infected, is, of course, very desirable. 

 Similarly in the nurseries there should be no delay in getting rid 

 of infected material, and as a further step at this point, the young 

 budded trees should be given such pruning as is necessary to keep* 

 the disease in check, aided when needed by spraying. 



Pruning. 



Heretofore it has been customary for writers on this subject to 

 advocate the pruning of diseased leaves and twigs, and the removal 

 of scabby fruit as important points in control. Recent observations 

 made in groves, where such steps have been taken, have made it 

 appear that no particular good is accomplished, and that, at best, 

 results sufficient to pay for th(^ expense involved are not received. 

 It appears that no matter how thoroughly scabby material is removed, 

 reinfection occurs in a propitious season, and apparently with un- 

 diminished intensity. Moreover, there must be considered the effect 

 on the trees of removing such a large proportion of the bearing sur- 

 face as is often involved in work of this kind. 



On a small scale — that is to say, in small isolated groves or 

 blocks of trees, or in instances where but a very few trees are in- 

 volved — pruning, if properly performed, can.be made effective. All 

 scabby growth must be removed, and the trees examined sufficiently 

 often to ket^p out all such material. When it is realized, that a 

 single scabby fruit or cluster of leaves left after pruning, will suf- 

 fice to reinfect the tree and probably others adjoining as well, the 

 necessity of great care in this work will be seen. It will also be 

 clear that the limit of practicability in this regard (number of 

 trees that can be handled) is soon reached. 



Tt lias l)een observed that scab often makes a beginning in a 

 grove by infecting over a period of several years one or a few trees 

 only, scattered about through the planting. After gaining sufficient 

 headway in these susceptible trees, it spreads over the balance of 

 the grove, often in a single season. When such instances have been 

 found, the budding over of the trees, using buds from nearby, thrifty, 

 scab-free trees, has been recommended. Such a course, it is thought, 

 will in the long run prove more effective than a series of prunings. 



