280 THE MONTHLY BULLETIN. 



It should be pointed out that many new roots were getting close to 

 the infected areas and would soon have become infected, so that if the 

 ditch is made once and not reopened the trouble will be only slightly 

 delayed and the work will hardly be worth while. Some orange roots 

 which were cut off in working the ditch remained alive in the soil for 

 more than two years and were pushing out growth from the cut end 

 which might have become a leafy shoot. This is an important matter 

 because it shows that a long time must elapse before roots will be 

 entirely decayed in the soil. 



Treating the Diseased Area. 



Soil sterilizing. Carbon bisulfid. It would not seem to be a diffi- 

 cult matter to find some substance which could be put into the soil 

 and entirely kill everything. Carbon bisulfid is the most promising 

 material thus far suggested. If used properly and in sufficient quan- 

 tity I feel sure it will do the work. It is simply a matter of studying 

 out the method and counting the cost. I feel rather doubtful if it will 

 be possible to kill the fungus and not kill good roots lying in the soil, 

 because the fungus penetrates into the wood and part of it is deeply 

 buried, while the living part of roots is the cambium layer, just between 

 the bark and wood. The way carbon bisulfid spreads and works in 

 the soil may be illustrated by one experiment. A row of holes was 

 bored with a small soil augur one foot apart and about fourteen inches 

 deep. One ounce of carbon bisulfid was poured into each hole and it 

 was filled and tamped with the heel at once. This row of holes passed 

 •just at the edge of the branches of a good orange tree. 



After a little more than two months, part of this row of holes was dug 

 out. Roots near the surface of the ground were found dead a little 

 more than a foot on each side of the holes while the deepest roots (less 

 than three feet) were killed nearly three feet from the holes. There 

 was no way to guess how deeply the material was effective but evidently 

 it would be for a good way. Wetting or covering the soil after inject- 

 ing the carbon bisulphide will probably be more important than the 

 amount used. We have taken a treatment of injecting 1^ ounces at 1^ 

 feet each way as a sort of standard for experimental purposes. I am 

 convinced that the treatment is worthless if the material is injected into 

 dry, loose soil. I do not j'^et have a precise method worked out which 

 can be depended on, but there is much hope of getting such a treatment 

 in the future. 



Ways of utilizing the infected areas are by planting annual crops or 

 resistant trees, if they can be found. Such areas have sometimes been 

 used by well meaning growers for nurseries. The nursery would prob- 

 ably grow very well so far as could be observed, but it will be clear that 

 such planting is highly undesirable. I have found spring replants 

 badl}^ infected the following fall. Of resistant trees the pear is 

 decidedly the favorite in California, and I have no definite data to 

 oppose to this view. However, I understand that the pear is not entirely 

 immune in the states north of us nor east of the Rocky Mountains. 

 Black walnut, cherry, apple and fig probably all possess decided resist- 

 ance. I can only advise caution in replanting diseased areas with 

 supposedly resistant trees. The strain of heavy fruit bearing and 

 occasional bad seasons mav reduce resistance in some cases. I would 



