18 CIRCULAR 3 6 5, U. S. DEPARTMENT OF AGRICULTURE 



It is better to use a low concentration of gas and repeat the fumiga- 

 tion in a week or 10 days than to risk burning the plants. 



The procedure for fumigating greenhouses and nurseries is given in 

 more detail in a Farmers' Bulletin (17) . 



SUMMARY 



The camphor scale was first discovered in injurious numbers in 

 Louisiana in 1920, probably having been introduced into the United 

 States from Japan. It is now generally distributed in southern 

 Louisiana, and isolated infestations exist in Mississippi, Alabama, and 

 Texas. 



The scale has been found on nearly 200 host plants. Camphor-tree, 

 Satsuma orange, Japanese privet, glossy privet, common camellia, 

 sweet osmanthus, roses, confederate- jasmine, and Kaki persimmon 

 are important host plants that may be heavily infested in Louisiana. 

 Apple trees were severely attacked when artificially infested. 



The minimum time required to complete a generation is 51 days, 

 but this period is considerably lengthened by low temperatures. 

 There are three complete generations each year, and in some years 

 a partial fourth generation may develop. The majority of the scales 

 pass the winter in the adult stage, but there is no well-defined hiberna- 

 tion period. The number of eggs beneath the coverings begins to 

 increase in January, and emergence of young may commence in 

 February or March, depending on the temperature. 



Although natural enemies may appreciably reduce the infestation 

 in limited areas, they cannot be relied upon to control the scale. 



Emulsions of petroleum oil make the most effective sprays. Several 

 formulas are given for preparing such emulsions. 



Highly refined oils are less toxic to plants than the less refined 

 oils, and they are fully as toxic to the camphor scale. They are 

 somewhat more expensive than oils that have been given less refine- 

 ment. The efficiency of an oil emulsion against the scale increases 

 with the viscosity of the oil, an oil having a viscosity falling within 

 the range of 100 to 200 seconds Saybolt being recommended. The 

 volatility of petroleum oils is not an important specification for 

 insecticidal purposes. 



The most important spray is a winter application using 2.5 to 

 3 percent of oil. Heavy infestations of the scale cannot be controlled 

 by one spraying, and the winter application must be supplemented 

 with sprays during the spring or summer. 



The emulsions used in summer sprays should be diluted at the rate 

 of 1 part of emulsion to 50 or 60 parts of water. A table is given 

 to show the best time to make these applications. 



Fumigation with hydrocyanic acid gas is also an effective means of 

 control for nursery stock and for many greenhouse plants. A dosage 

 schedule is given for this treatment. The maximum dosage recom- 

 mended for growing plants will not kill all the eggs at temperatures 

 below 80° F. 



