EFFECT OF FUMIGATION ON TREES, 53 



tree as a whole. This tree was observed in full bloom on April 4, and 

 ten months after the treatment appeared as vigorous as any tree in 

 the grove and bore more than the average crop of fruit. In the 

 experiments with the bell tent of 6i-ounce drill, shedding of conse- 

 quence occurred only in the case of experiment X.2. This tree was 

 fumigated on January 29, beginning at 4.41 and ending at 7.50 p. m. 

 It was estimated that the shedding amounted to about 30 per cent 

 in this case. 



In experiment 45.36 the exposure began at 3.07 p. m. in bright sun- 

 light with the temperature at 75° F. The tent had been in position 

 for thirty minutes preceding the introduction of the chemicals, and 

 the inside temperature was 4^° higher at the beginning than the out- 

 side temperature mentioned above. The tent was in direct sunlight 

 during the entire forty-five minutes of exposure, and doubtless the 

 inside temperature rose to 82"^ or 83°. As shown in Table IV, the 

 amount of potassium cyanid used was 44 ounces less than the 

 amount recommended in the table given in the appendix. The 

 leaves were curled as a result of drought at the time of the fumiga- 

 tion and no shedding of leaves or injury of any kind to the tree could 

 be detected by subsequent examinations. 



An overdose is indicated by the scorching of the foliage on entire 

 twigs. This is more likely to occur near the tops of the trees. In 

 such cases several twigs, each 6 inches or a foot in length, may be 

 entirely killed, the leaves, instead of dropping within a few days, 

 turning brown and remaining attached to the dead twig. This is 

 not necessarily accompanied by excessive shedding of the foliage. 

 The physiological condition of the trees seems to have a marked 

 effect on their liability to shed foliage. Vigorous trees are less 

 susceptible than weak, poorly nourished ones. Trees in the same 

 grove but growing under different conditions as regards the nature 

 of the soil and the amount of soil moisture show differences in this 

 respect. In most groves trees will not shed leaves excessively if 

 the dosage is increased 25 per cent above the recommended amounts. 

 Frequently there will be no shedding at all following such a course. 

 In other citrus groves the recommended dose is as large as the trees 

 will stand without shedding to an injurious extent. 



The likelihood of damaging citrus fruits by fumigation is such that 

 it is strongly advisable to pick the crop before starting to fumigate. _ 

 In January, 1908, many seedling trees were fumigated which held 

 from five to eight boxes of oranges per tree, without any injury 

 whatever following the treatment. In other cases a small percent- 

 age of the fruit developed sunken areas or "pits" which turned dark 

 and ruined the affected fruit for shipping purposes. Fumigation 

 in midwinter, using the dosage table given in the appendix, does not 

 seem to affect the fruit of Hart's Lake, Lamb's Summer, or Valencia 



