20 



The Weekly Florists^ Review* 



May 2, 1912. 



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LATEST FACTS s^ 

 a>e ON FUMIGATION 



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33 



BESULTS OF BECENT BESEABCH. 



The Problem. 



Ever since the development of the 

 idea that the destruction of our crops 

 by insects was not necessarily the will 

 of the Creator, the importance of con- 

 trolling these pests has been realized 

 and various methods have been em- 

 ployed for the purpose. 



Briefly stated, the problem is: How 

 can we destroy one form of life while 

 it is on another form of life, without 

 destroying or at least injuring the lat- 

 ter? How can we destroy the living 

 substance or protoplasm of the insect 

 at a time when it is in close contact 

 with another living substance, without 

 the destruction of both? 



This is comparatively easy of solu- 

 tion in the case of chewing insects, as 

 poisons which will not injure the plant 

 can be placed upon it, for consumption 

 by the insect. But most of our worst 

 pests do not feed in this way, but by 

 sucking the sap from inside the plant, 

 and for such pests stomach poisons are 

 of no avail. For these insects the logi- 

 cal complement to the stomach poison, 

 therefore, is the contact insecticide, 

 which destroys the insects which it 

 touches. Difficulties at once arise, how- 

 ever, in carrying out this idea, as 

 many of the insects of this class are 

 exceedingly minute and correspond- 

 ingly difficult to reach with the spray. 

 Others, in addition, seem to delight in 

 locating in places where there is little 

 opportunity ^ get at them, while 

 others, still, are so thoroughly protected 

 by covering scales, waxy threads or 

 other repellent structures that a con- 

 tact insecticide strong enough to pene- 

 trate these protections and destroy the 

 insects becomes dangerous to the plant 

 the insects are on. 



The Need of Caution. 



It is only natural, therefore, realiz- 

 ing that insects must breathe, and re- 

 membering that gases penetrate every- 

 where, that the idea of overcoming the 

 difficulties mentioned by using poison- 

 ous or suffocating gases should have 

 been received with favor. Even by this 

 method, however, danger of injury to 

 the plant life cannot be avoided, for 

 we must recognize from what has al- 

 ready been said that the living sub- 

 stance of a plant is liable to destruc- 

 tion by anything which will cause the 

 death of the living substance of an 

 animal on it. We should, therefore, ex- 

 pect to be able to kill by fumigation 

 only such insects as are less resistant 

 than the plants they are on. This is 

 probably the reason why most fumiga- 

 tions in the past have been made so 

 weak that the results were often unsat- 

 isfactory. It is only natural to be cau- 

 tious in work of this kind, but caution 



A paper by H. T. Fernald, Ph. D., entomologist 

 at the Massachusetts Agricultural College, Am- 

 herst, Mass.. read before the florists during 

 Farmers' Week at Amherst. 



which gives a fumigation so weak that 

 the most delicate insects fail to be de- 

 stroyed is merely a waste of time and 

 money. 



Of the various fumigi.,nts, sulphur 

 has probably been used the longest. 

 But sulphur apparently acts as vigor- 

 ously on plants as on animals, which 

 means that fumigation with this sub- 

 stance at an effective strength is liable 

 to produce disastrous results. The safest 

 time to use sulphur is when a 

 house is empty, using a strong dose, to 

 clear out any insects which may be 



The Editor Is pleased 

 w^hen a Reader 

 presents Ills Ideas 

 on any subject treated In 



tV»^ 



As exi>erlenoe is the bent 

 teacher, so do 'we 

 learn fastest by an 

 exchanse of experiences. 

 Many valuable points 

 are brouBht out 

 by discussion. 



Good penmanship, spelling and 

 fframmar, though desirable, are not 

 necessary. Write as you would talk 

 when doing your best. 



WK SHAIX BX GLAD 

 TO HKAR FROM TOU 



present and which might attack the 

 next crop put in. 



Tobacco as a Fumigant. 



Tobacco as a fumigant needs little 

 comment. The active substance, of 

 course, is nicotine, of which in ordi- 

 nary tobacco there is, on an average, 

 only about four or five per cent — not 

 enough to accomplish anything like 

 thorough work. Vaporized, it will kill 

 some plant lice, some thrips perhaps, 

 and some adult white flies. But in 

 every case certain stages of these in- 

 sects, which are more resistant, remain 

 unaffected and from them the house is 

 soon restocked with trouble. 



To overcome this difficulty of the 

 weakness of tobacco, extracts of vari- 

 ous kinds containing larger amounts of 



nicotine have been placed on the mar- 

 ket. These are, of course, more effi- 

 cient, but even with them the more re- 

 sistant stages of many pests survive 

 until for their destruction it is neces- 

 sary to use such a large amount of the 

 material that the expense of treatment 

 makes it prohibitive. 



Hydrocyanic Acid Gas. 



Hydrocyanic acid gas is perhaps the 

 most active poisonous gas known — at 

 least, at all well known. It can be 

 produced from various chemicals, but 

 until recently it has generally been ob- 

 tained by adding sulphuric acid to po- 

 tassium cyanide. It has been used ex- 

 perimentally, and by comparing results 

 a general rule for its production and 

 application has been outlined and pub- 

 lished and has come into quite general 

 use for greenhouse work. Strangely 

 enough, however, just what amounts of 

 the various materials should be taken, 

 and the best grades of these for the 

 purpose, have only recently been care- 

 fully investigated and the results of 

 this work have not as yet become widely 

 known. Let us consider the materials 

 and methods of cyanide fumigation, 

 then, in some detail. 



There must be a standard estab- 

 lished in the production of the gas, if 

 results are to be compared and conclu- 

 sions drawn with any safety. The man 

 who fumigates at a supposed certain 

 strength of cyanide, but who uses the 

 fifty per cent cyanide, which is the 

 usual strength kept at drug stores, in- 

 stead of the ninety-eight to ninety-nine 

 per cent material, will of course get re- 

 sults widely different from those ob- 

 tained by persons using the stronger 

 article. We must use standard mate- 

 rials, then, if we use the same formula 

 in their preparation. 



Purity of the Cyanide. 



Three materials are necessary — ^po- 

 tassium cyanide, sulphuric acid and 

 water. We have to consider their qual- 

 ity and the quantity to use. 



It is important to use a cyanide 

 which is practically pure. The ninety- 

 eight to ninety-nine per cent grade 

 manufactured by Merck is a reliable 

 material, and the products of similar 

 strength made by a number of other 

 manufacturers are also satisfactory. 

 With^ower grades less of the material 

 from which the gas is formed is, of 

 course, available, and there is also a 

 question as to what result the presence 

 of other substances may produce. With 

 a fifty per cent cyanide, for example, 

 there would be only about half as 

 much cyanogen to combine with the 

 hydrogen of the sulphuric acid as with 

 the ninety-eight to ninety-nine per cent 

 grade, and if among the constituents 

 of the other fifty per cent there should 

 be something which would combine 



