37 



the gas continuing over night, caused no injury; but it is probable 

 that the house used for these tests was not as tight as the Massachu- 

 setts one, as this strength injured the plants in this State. 



It is necessary to be sure of the quality of the cyanide used in fumi- 

 gation. Most drug stores carry a grade of about 50 per cent strength; 

 but it is necessary to obtain the 98 to 99 per cent strength, to be at 

 all certain of results. This should be obtained in one pound sealed 

 cans, which state the strength on the outside, and which should not 

 cost over 50 cents per pound. The commercial grade of sulfuric acid 

 is as good as is needed, and its costs should not be more than 10 cents 

 per pound. From this it can be seen that fumigation with cyanide 

 is not an expensive process. 



At the present time our knowledge is not sufficient to enable us 

 to use the gas strong enough to kill all the insects. A single fumiga- 

 tion well below the point of danger to the plants will kill the plant lice, 

 most of the white fly, thrips, and some of the mealy bugs. Against their 

 eggs, however, and against most scale insects, it is of little value. But 

 the eggs will soon hatch, and a repetition of the treatment will then 

 reach the young which hatched after the first fumigation. In practice 

 it has been found that fumigation with one-third of an ounce of cyanide 

 to each thousand cubic feet in the house, repeated three times at 

 intervals of twelve to fourteen days, will practically free a house from 

 insect pests except scales and red spiders. 



This holds good for tight houses only. If the house is loose and 

 much of the gas becomes quickly lost, larger amounts must be used, 

 but how much larger these may be will depend entirely on how loose 

 the house is. 



Where the house is a long one, it is well to divide the charge into two 

 or more equal parts, and start the fumigation at the jar farthest from 

 the door; then drop the other charges of cyanide into their jars as 

 these are passed on the way out. 



Dipping. 



Dipping wherever this is possible is much better than spraying, as , 

 the entire plant is reached, while this is practically impossible by 

 spraying. As only potted plants can be dipped, however, it is often 

 necessary to resort to spraying instead. 



Tobacco water, made by steeping tobacco leaves and stems in hot 

 water, is a good insecticide for plant lice, mealy bugs and thrips, but 

 weak solutions are far from effective. The use of laundry soap also gives 

 good results, though for many plants more than four ounces per 

 gallon of water is not safe for the plant, while ineffective against the 

 insects. As a general thing, though, it would be well to try the soap 

 before resorting to tobacco water. 



For scale insects laundry soap is usually too weak to be of much 

 value, and whale-oil soap must be used. Fortunately, most cycads, 

 palms and citrus plants can withstand this when used even as strong 

 as one pound per gallon of water, though ferns are injured by such 

 a strong solution. 



To dip potted plants rapidly, a tall can filled with the soap is a 

 great convenience, particularly if as tall as are the plants to be dipped. 

 Turn the plant bottom up and plunge it into the can till the wash 

 reaches the bottom of the stem, and hold it there a few moments, 

 then remove it and let it drain before putting it back in its place. In 

 some cases it may seem advisable to wash the plant with clean water 

 after a few hours. 



