10 BULLETIN 513, U. S. DEPARTMENT OF AGRICULTURE. 
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 fiorist’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, white 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 
4 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 
cubie 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 
eyanid per 1,000 cubic feet it a cost of 1 cent per 1,000 cubic feet. A 
single Be ication 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 
14 cents per 1,000 cubic feet. The standard proprietary insecticides 
