NAPHTHALENE AS A GREENHOUSE FUMIGANT 



By W. D. Whitcomb, Research Professor of Entomology 



INTRODUCTION 



In a greenhouse where confined gases will penetrate all available areas and 

 where they can be discharged with a reasonable amount of labor and expense, 

 fumigation is the ideal method of pest control. Unfortunately, however, the 

 standard fumigating materials containing nicotine and hydrocyanic acid gas, 

 which satisfactorily control the majority of greenhouse insect pests, do not 

 effectively control the common red spider at concentrations and exposures 

 which can be safely used on most greenhouse plants. Naphthalene fumes have 

 a specific toxic action on the common red spider and other pests; and when 

 certain factors such as temperature, relative humidity, dosage, and length of 

 exposure are controlled, fumigation with naphthalene is a safe and effective 

 treatment on many species of greenhouse plants. 



DESCRIPTION OF NAPHTHALENE 



Naphthalene is an organic chemical compound having the symbol C 10 H 8 

 and is produced by the destructive distillation of coal. When pure it forms 

 flat colorless crystals having a penetrating but not unpleasant odor and a 

 burning aromatic taste. The fumes are irritating to the eyes, usually inducing 

 tears, but reasonable exposure to them is not harmful. Naphthalene melts 

 at 80.1° C. (176.2° F.) and boils at 217.9° C. (424.2° F.). The crystals volatilize 

 slowly at about 70° F. and this action increases with the amount of water 

 vapor in the air. They are insoluble in cold water but can be dissolved in 

 ether, alcohol, and other organic solvents. 



Naphthalene finds its greatest use in the dye industry where, in combination 

 with other chemicals, it is used in the manufacture of various colors, especially 

 red and yellow. It is prepared for commerce in a crude form (bags) both 

 domestic and imported, flake form (barrels), dyestuff (bags\ and as the well- 

 known moth balls (barrels) where it may be combined with camphor. The 

 retail price for the commercial forms ranges from 8 to 12 cents a pound. A 

 resublimed form (100 percent pure) is available in limited quantities at a con- 

 siderably greater cost. 



Naphthalene which is to be used for fumigating living plants should be 

 approximately 95 percent pure. The principal impurities are forms of unrefined 

 coal tar, the fumes of which are injurious to plant life. Crude naphthalene, 

 which is the cheapest commercial grade, contains variable quantities of these 

 impurities and its analysis is neither guaranteed nor constant. Resublimed 

 naphthalene is the purest form which is commercially available and was used 

 in the first work with this material for greenhouse fumigation. Commercial 

 flake naphthalene is a very nearly pure product which has been found entirely 

 satisfactory for fumigating, and this form was used in the experiments reported 

 herein. 



