28 MASS. EXPERIMENT STATION BULLETIN 326 



the required time, it is usually advisable to stop the fumigation and change 

 the air in the greenhouse; but if the naphthalene has vaporized too rapidly 

 in only one or two lamps the danger of plant injury is not great and the fumiga- 

 tion can usually be continued after adjusting the lamps. 



If the temperature unavoidably rises above 95° F. or drops below 70° F. 

 during the exposure, the fumigation should be discontinued and the house 

 ventilated. 



When pipe heat is used to maintain the necessary temperature, the relative 

 humidity may decrease rapidly making it advisable to wet the walks after the 

 third hour. 



After the fumigation is completed, the air in the greenhouse should be changed 

 by opening the doors and ventilators. In cool weather this should be done 

 gradually to avoid a rapid drop in the air temperature. 



SUMMARY 



Commerical flake naphthalene, costing 8 to 12 cents a pound, when vaporized 

 in the greenhouse controls the common red spider and the greenhouse thrips 

 very effectively and is a satisfactory method for combating these and other 

 pests. 



Naphthalene fumes kill by penetrating the respiratory system of insects and 

 spiders causing paralysis and death. 



Eggs of the red spider were killed by two or more successive fumigations 

 using 3 ounces of naphthalene per 1,000 cubic feet for 6 hours, and old eggs 

 were killed more quickly than newly laid eggs. The larva, protonymph, and 

 adult female of the red spider appear to be more easily killed than other stages. 

 Two successive fumigations at a dosage of 2 ounces or more of naphthalene per 

 1,000 cubic feet have resulted in practically perfect control of red spider under 

 favorable experimental conditions. Dosages of more than 3 ounces of naph- 

 thalene per 1 ,000 cubic feet have frequently caused supersaturation and plant 

 injury, and dosages of less than 2 ounces per 1,000 cubic feet have usually 

 required more than two successive treatments to be effective. 



In controlled experiments the vaporization and confinement of three-fourths 

 ounce of naphthalene per 1,000 cubic feet produce a noticeable effect on the 

 red spider, and an exposure to this concentration for three hours has killed 

 85 percent or more of these pests. Under average greenhouse conditions some 

 of the fumes escape or are absorbed by the soil and benches so that the most 

 satisfactory dosage is 2 to 3 ounces per 1,000 cubic feet, and a total exposure 

 of 6 hours is recommended for effective results. 



In commercial greenhouses where it is difficult to maintain favorable atmos- 

 pheric conditions, three or four successive fumigations are frequently necessary 

 to give effective control. The treatment is satisfactory whether the interval 

 between fumigations is one, two, or three days, and the time to fumigate should 

 be determined by suitable weather conditions. 



Although various types of stoves, lamps, and special saturators are available 

 for vaporizing naphthalene for fumigating, a two-wick coal-oil stove is the most 

 practical under average greenhouse conditions. In these stoves the crystals 

 are melted to increase vaporization but the melted naphthalene should never 

 boil. A uniform vaporization can be obtained by dividing the total dosage for 



