10 BULLETIN" 513, U. S. DEPARTMENT OF AGEICULTURE. 



absence of the owner on a vacation is prevalent over the entire coun- 

 try, and often results in establishing pests not hitherto known to 

 occur on the florist's premises. If the trade requires such a practice, 

 plants of this character should be cleaned thoroughly of insect pests 

 before being placed with the regular stock of the greenhouse. 



Insect infestations in greenhouses have been traced to the following 

 sources : Infested plants brought in from cold frames or propagation 

 beds which have not received proper attention ; cuttings, plants, and 

 buds received from other establishments; and imported foreign or 

 domestic stock. Adults of the greenhouse white fly, grasshoppers, 

 beetles, aphids, etc., may enter through open ventilators from other 

 houses or gardens; cutworms, wireworms, wdiite grubs, etc., may be 

 brought into the house with the soil; and roaches, ants, sowbugs, 

 millipeds, etc., are sometimes brought in with packages, or they may 

 crawl into the house through small openings. 



COST OF HYDROCYANIC-ACID GAS FUMIGATION. 



The economy in the use of hydrocyanic-acid gas as a means of con- 

 trolling aphids, white flies, thrips, and the common greenhouse scale 

 insects is apparent from the following figures, which are based on 

 current prices: 



Aphids can be controlled with a single fumigation at the rate of 

 one-fourth ounce per 1,000 cubic feet at a cost of approximately 

 i cent per 1,000 cubic feet. Tobacco fumigation with standard 

 tobacco paper costs from 1^ to 3 cents per 1,000 cubic feet, and to 

 secure a satisfactory control the operation must be repeated several 

 times. Standard nicotine soap solution costs from 1 to 3 cents 

 per gallon, and 4 gallons are required to cover plants which would 

 occupy 1,000 cubic feet of space. 



The greenhouse white fly can be controlled in three successive 

 fumigations at the rate of one-half ounce of sodium cyanid per 1,000 

 cubic feet, with a total cost of 3 cents per 1,000 cubic feet for a com- 

 plete control. Standard insecticides cost about 6 cents per 1,000 

 cubic feet for a single application, and fully four applications are 

 required for a satisfactory control. 



Thrips can be controlled on such plants as azaleas, lilies, and ferns 

 with a single fumigation at the rate of one-half ounce of sodium 

 cyanid per 1,000 cubic feet at a cost of 1 cent per 1,000 cubic feet. A 

 single application of nicotine soap solution costs fully five times as 

 much as the gas treatment and still gives only a partial control. 



The common scale insects of greenhouses (excepting mealy bugs) 

 can be controlled by fumigating the infested plants at the rate of 

 three-fourths ounce of sodium cyanid per 1,000 cubic feet at a cost of 

 1^ cents per 1,000 cubic feet. The standard proprietary insecticides 



