10 BULLETIN 907, TJ. S. DEPARTMENT OF AGRICULTURE. 



MOISTURE. 



The effect of moisture on fumigated citrus trees is shown in experi- 

 ments 4, 6 to 9, and 11, in which varied prefumigation conditions 

 occur. In Nos. 4, 8, 9, and 11a number of plants in the shade at 

 temperatures between 60° and 68° F. were drenched with water 

 before they were placed in the fumigatorium with others having 

 perfectly dry foliage, and were then immediately subjected to 

 hydrocyanic-acid gas. Thirty-seven plants in all were used in these 

 four experiments and in no case was. there any apparent difference 

 in injury between the wet and the dry plants, even though a num- 

 ber of the trees had some very tender foliage. 



In experiments 4, 6, and 7 plants were exposed to prefumigation 

 sunshine at temperatures ranging from 67° to 80° F. Immediately 

 before fumigation a part was drenched with water and afterwards 

 fumigated with others having perfectly dry foliage. Experiment 6 

 exhibits the same degree of injury for the wet plants as for the dry, 

 a condition which holds true whether the water used in the treatment 

 was 58° or 86° F. In experiment 4 the dry plants were slightly 

 more severely injured than the wet, quite the contrary to what 

 would be expected, and in fact to what is shown by Moore (11) to 

 take place in the case of tender greenhouse plants. In experiment 7 

 the dry plants were likewise more severely injured than those treated 

 with cool water, although where wet with warm water the injury 

 was equal. While these two experiments are insufficient in them- 

 selves to prove definitely that plants subjected to a hot sunshine 

 before fumigation are more severely injured when dry than when wet 

 it at least indicates that the wetting of such plants can, in some cases 

 at least, reduce the degree of injury to an extent. In this connection 

 it should be noted that the reduction of injury to the wet plants 

 occurred where the water used was at a temperature considerably 

 lower than that of the sunshine. Water at a temperature equal to 

 or higher than the sun temperature did not appear to influence the 

 degree of injury over that normal to dry plants. 



In conclusion it may be stated that water on citrus plants appears 

 in no way to affect the degree of injury, if the plants are subjected 

 to shade or darkness before treatment; if, however, plants are in the 

 direct sunshine before treatment, water appears to reduce the injury 

 slightly, at least in some cases where the temperature of the water 

 is below that of the sunshine. 



THE EFFECT ON PLANT INJURY OF TEMPERATURE, LIGHT, AND MOIS- 

 TURE AFTER FUMIGATION. 



Fumigation with hydrocyanic acid is usually considered completed 

 with the separation of the treated plants from exposure to the gas. 

 Little or no attention has been given to the postfumigation environ- 



