52 FUMIGATIOX INVESTIGATIONS IN CALIFORNIA. 



Experiment No. 3. — On Jul}' 11 and 13, four Valencia orange trees 

 were fumigated, using a l|-ounce dosage rate, 4 trees receiving a 

 l^-ounce dosage, 8 trees a l|-ounce dosage, and 4 trees a 2-ounce 

 dosage. These trees were in a perfectly normal condition, about 

 7 to 8 feet high, and contained young fruits fully three-fourths of an 

 inch in diameter. With the l|-ounce dosage rate no fruit was 

 burned; with the H-ounce rate an occasional orange was slightly 

 burned; with the l|-ounce rate a very small percentage was burned, 

 while with the 2-ounce rate a considerable percentage was injured. 

 This demonstrates that a 2-ounce dosage rate could not be safely 

 used on trees of this size. 



Experiment No. 4- — During the middle of July a large number of 

 orange trees of all sizes were fumigated at Santa Fe Springs, Cal., 

 using various dosage rates. The trees fumigated were of several 

 varieties, in a healthy condition, and all well filled with fruits about 

 the size of an English walnut and slightly larger. It was found from 

 this experiment that a dosage rate of 1 ounce to 100 cubic feet could 

 at this time be used without injury on orange trees 15 to 16 feet high. 

 Only an occasional orange was burned by Ij ounces. Smaller trees 

 proved able to stand a heavier dosage than larger ones without 

 appreciable injury. 



On the basis of information obtained from experiment No. 4, 

 dosage schedule 1 (p. 65) was prepared. This schedule was put into 

 use during the latter part of July and has been in use, up to the 

 time of writing, by two outfits, at Whittier, Cal. Although no 

 noticeable injury to the fruit has resulted from the use of tliis dosage, 

 the general effect on the tree has indicated that a heavier dosage 

 could not have been used with safety. 



A further example of the tender nature of small fruits was shown 

 in some work done by an excellent fumigator at Downey, Cal., during 

 the latter part of RIay. The fruits were for the most part three- 

 eighths of an inch or less in size, while the trees were thoroughly 

 infested with scale and in a generally unhealthy condition. So far 

 as could be determined, a dosage rate of approximately three-fourths 

 to 1 ounce was used. The larger percentage of the fruits on these 

 trees was burned. Other instances of like fumigation, where the 

 fruits were one-fourth inch or less in diameter, have been seen. The 

 fruit at this period is very tender. Doubtless it is the most critical 

 period of any during which fumigation is conducted. 



From the foregoing, it is evident that heavy dosage can not be 

 used while the fruits are small without more or less injury, and that 

 the most critical period during which fumigation may be conducted 

 is between the time when the fruits are set and the time when they 

 attain the size of a walnut. 



