68 HYDROCYANIC-ACID GAS FUMIGATION IN CALIFORNIA. 



During this investigation many acres of perfectly healthy trees free 

 of insect pests have been treated throughout the period of several 

 months preceding blossoming up until the blossoms fall. No effect 

 producing an increase or perfection of the coming crop of fruit has 

 ever resulted from these efforts. Although the acreage treated has 

 not been sufficiently great to justify the absolute statement that 

 fumigation, in itself, never produces a greater crop of fruit, never- 

 theless the negative results in all the orchards treated certainly prove 

 that if an increased crop ever results it is of infrequent occurrence and 

 under peculiar conditions. 



EFFECTS OF METEOROLOGICAL ELEMENTS ON FUMIGATION. 



MOISTURE. 



The great affinity of water for hydrocyanic-acid gas is well known. 

 Writers on greenhouse fumigation contend that the plants should be 

 dry when treated, else injury might result. It has been the universal 

 opinion among California fumigators that if the fumigation treatment 

 was carried on while the trees were wet injury might follow. Gos- 

 sard, 1 and more recently Morrill, 2 assert that moisture does not pro- 

 duce injury to the fruit and that the destruction of insects is as great 

 under wet as under dry conditions. Quaintance 3 has corroborated 

 these results of Gossard and Morrill where the work is done on moist 

 fruit (apples) in cold storage. 



The fumigation work which has been performed by the Govern- 

 ment outfit during this investigation has been carried on in all sections 

 of southern California, at all times of the year, and under all conditions 

 of weather — when the trees were entirely dry, when the trees were 

 wet, so wet that the moisture was falling off in drops, and when it was 

 raining. Mr. G. R. Pilate, a temporary assistant, was stationed with 

 a practical outfit during October, November, and December, 1909, 

 at Rivera and Downey, than which the writer believes there is no 

 generally damper citrus section in California. Careful records were 

 kept of all the climatic elements which might affect fumigation. 

 These records show that almost every night the trees became thor- 

 oughly moistened before the work was discontinued. In addition to 

 this, the results of the treatment of hundreds of acres by other prac- 

 tical outfits have been followed during the writer's residence in 

 southern California. 



From all this experience not a single authentic instance has been 

 seen in which burning was directly attributable to absorption of gas 

 by the moisture on the fruit or leaves. Thus the writer has felt justi- 

 fied in concluding that the presence of moisture on trees can be ignored 



• Bui. 67, Fla. Agr. Exp. Sta., pp. 647-648, 1903. 



2 Bui. 76, Bur. Ent., U. S. Dept. Agr., pp. 12-14, 1908. 



s Bui. 84, Bur. Ent., U. S. Dept. Agr., pp. 24,31, 1909. 



