22 BULLETIN 833, U. S. DEPARTMENT OF AGRICULTURE. 



When a severe infestation is encountered the most heavily infested 

 plants should be taken out immediately and burned. 



This should then be followed by either fumigation or spraying as 

 outlined below. 



Fumigate every night, with either nicotine papers or hydrocyanic- 

 acid gas, for a period of at least six weeks. This will kill all the 

 adults that emerge during such a period and at the same time will 

 prevent the further laying of eggs for future generations. The 

 dosage need not be very heavy in either case. When nicotine papers 

 are used one sheet to every 1,000 cubic feet of space will suffice. 

 If hydrocyanic-acid gas 1 is employed, one-eighth to one-fourth ounce 

 per 1,000 cubic feet will kill all of the adults. The use of hydro- 

 cyanic-acid gas is not recommended unless in the hands of a competent 

 fumigator, owing to its deadly poisonous effects. Too much emphasis 

 can not be laid on the fact that the fumigation must be set off after 

 12 o'clock, midnight, to be effective. It is preferable to start the 

 generation between the hours of 12.30 a. m. and 2 a. m. Any fumi- 

 gation done before midnight would be useless for it has been pointed 

 out that the adult does not emerge until after midnight. On the 

 other hand, if it is started later than 2 a. m. many adults will have 

 emerged and laid their eggs. 



In case fumigation is not advisable, especially where chrysanthemum 

 plants are isolated or when other varieties of plants are present in the 

 houses, spraying is recommended. This must be done consistently for 

 a period of four to six weeks, a 40 per cent solution of nicotine sul- 

 phate extract diluted (1-800) being used, and soap added at the rate of 

 one-half to 1 ounce per gallon of solution. The application should be 

 made late in the afternoon in order that the best results may be 

 obtained. In this manner practically all adults can be killed at the 

 time of emergence and any eggs present will be destroyed. 



PREVENTIVE MEASURES. 



It has been proved that the means of disseminating this insect 

 has been the shipment of infested chrysanthemums, both plants and 

 cuttings. Interceptions made by the various State inspection 

 officials, as well as by inspectors of the Federal Horticultural Board, 

 definitely confirm this fact. It is therefore imperative that only 

 clean plants and cuttings be brought into commercial houses where 

 chrysanthemums are growing or to be grown. Growers should care- 

 fully examine all chrysanthemums received and see that all material 

 intended for shipment or distribution is free from this pest. Any 

 questionable material should at once be submitted to the State 



i For further information on the use of hydrocyanic-acid as in fumigating greenhouses, see Farmers' 

 Bullet! n 880. 



