66 HYDROCYANIC-ACID GAS FUMIGATION IN CALIFORNIA. 



resistant. As all three kinds of citrus are fumigated at the same 

 time, regardless of kind, it is necessary to base advice on the one most 

 susceptible to injury. If the tenderest kinds escape injury the more 

 resistant very naturally will do so. Hence, in reality the recommen- 

 dations in this bulletin are based on the orange, partly because of its 

 greater acreage but mainly because any recommendations made for 

 it will apply equally to the grapefruit or lemon. 



The lemon blossoms throughout the year in California, so that 

 different sized fruit may be found at all times. This is very different 

 from the orange, which has one regular crop. Lemons usually will 

 escape pitting or burning under conditions which might seriously 

 injure oranges. This allows a wider range of activity in fumigating 

 lemon trees. The work can be continued somewhat later in the 

 spring and commence earlier in the summer than with the orange. 

 In fumigating a section containing lemon and orange trees it is good 

 policy, where convenient, to commence on the lemons, leaving the 

 oranges until a later period. 



EFFECTS OF FUMIGATION ON UNHEALTHY TREES. 



Unhealthy citrus trees are found universally. Occasionally a 

 part or whole of an orchard is composed of trees weakened by lack of 

 such essential treatment as proper cultivation, fertilization, or irri- 

 gation. Many orchards contain trees weakened from attacks of a 

 gum disease, of "gophers" (ground squirrels), scale insect pests, 

 and numerous other causes which check their normal development. 

 These unhealthy trees are less resistant to injury from fumigation 

 than perfectly healthy ones. In examining results in an orchard 

 recently fumigated the writer has noticed frequently that the fruit 

 on a few trees that had been weakened by disease was severely pitted 

 or burned, while that on all healthy trees was uninjured. A heavy 

 dropping of fruit might have taken place in the unhealthy trees, while 

 the others were unaffected in any way. A most striking example 

 of severe injury to unhealthy trees was seen in an orchard fumigated 

 with double tents (one tent over the other) using a dosage twice 

 schedule No. 1. Healthy trees in some cases were severely burned 

 back at the top for about a foot, accompanied by the dropping of 

 some leaves, while the trees weakened by gum disease usually would 

 be burned back from 2 to 3 feet and drop practically all their leaves. 

 Severe injury to unhealthy trees has been seen even where the 

 three-fourths schedule was used. 



Practical fumigators have always been aware of the susceptibility 

 of weakened trees to injury and have decreased their dosage greatly 

 in treating such trees. The grower should not complain if the fruit 

 and leaves on their unhealthy trees are slightly injured. Such fruit 

 is normally of the inferior grades, while the damage caused by the 



