98 



wounds begin to heal. It is necessary, however, to shade the roots 

 from the sun. The diseased wool should be burned. Removal of the 

 entire tree is often wiser than trying to cure the disease. 



Value of Sour-Orange and Pomelo Stocks. - The "scaly bark" form 

 of gum disease has not been observed in California on the Florida sour 

 orange stocks. Such trees, budded to navel oranges two feet or more 

 from the ground, are growing near the substation. Some of them have 

 diseased trunks and branches, but in no case has the disease been 

 found extending down to the sour-stock. Evidently there would be 

 no advantage in using this resistant stock in low-budded nursery 

 trees, but sour-stocks might be planted in the orchard and allowed to 

 form the main branches of the future tree. Then should the " scalj'^ 

 bark" make its appearance, a few branches might be destroyed, but the 

 trunk would remain sound Since the sour-stock has not given uni- 

 versal satisfaction in Southern California, the pomelo, which seems but 

 little less resistant to " scaly bark" than is the sour-orange, and is a 

 more universally vigorous grower, may be used. The sweet-orange, 

 stock is the poorest of the three. 



The " Die-Bark" Trouble. — The third serious trouble is exanthema 

 or " die-back." This name is given to a weakness affecting orange, 

 lemon, and other orchard trees. There are several especially bad cases 

 in the San Gabriel Valley, where solid blocks of citrus trees are now 

 utterly worthless. Trees seven years old and in a frostless location 

 have not attained a height of over four feet, io some instances, and 

 bear little or no fruit, while adjoining trees of the same age and seem- 

 ingly under similar conditions are of large size and bear heavy crops. 



Orange trees affected with " die back" make an apparently healthy 

 growth in the spring and early summer, but the young shoots scon 

 turn yellow, the leaves drop off and the twigs die back to the older 

 wood from which a brown granular substance exudes. In a season or 

 two, this older wood also dies. Adventitious buds keep developing at 

 the axils of the leaves, until at the end of the season there are small 

 knots, where there should be healthy lateral branches. Experiments 

 with Bordeaux mixture and carbonate of copper have been made in a 

 badly affected grove near Pomona. The work so far has shown no ap- 

 preciable results, but it has not yet been carried through one season. 



[In almost all cases of " die-back," examination has shown some 

 fault in the subsoil, which puts the roots under stress. Such fault 

 m-y be an underlying hardpan or impervious cla}', pure and simple; 

 or it may be excessive wetness or dryness of the substrata surrounding 

 the deeper roots; or tl e rise of bottom water from below, iis in cases 

 of over-irrigation The true "die-back" i-« not properly a disease, but 

 simply the manifestation of the distress felt by the root-sj^stem under- 

 ground. The first thing needful is to dig down and examine the roots, 

 and then to relieve whatever fault may be found, if possible ; which 

 may not always be the case. Sometimes an appearance similar to thr- 

 " die back" is caused by the roots encountering a marly stratum, which 

 is apt to stunt the growth of the tree, causing it to put out a multitude 

 of small, thin branches, and sometimes causing the tips to die off. For 

 this form of the trouble there is no permanent remedy ; the trees 



