24 



The Weekly Florists' Review. 



Mat 9, 1912. 



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LATEST FACTS »e 



ON FUMIGATION 



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BESULTS OF RECENT BESEABCH. 



Thrips and Plant Lice. 



So far as we now know, thrips may 

 be killed by the use of nicotine extracts, 

 of which there are several on the 

 market. Recent tests of materials 

 containing forty per cent of nicotine 

 have been made, using an ounce to 

 every 1,000 cubic feet of space. The 

 extract was evaporated over small 

 lamps or stoves, and to prevent 

 scorching was considerably diluted 

 with water. It was carried on all night 

 in a moist atmosphere and the house 

 was not opened until morning. Every 

 thrips in the house was killed in this 

 way. A similar test with hydrocyanic 

 acid gas gave an equally good result, 

 but it is certainly unwise to use a gas 

 so dangerous to human life when a less 

 dangerous treatment proves equally ef- 

 fective. It should be remembered that 

 the house in which these tests were 

 made was probably rather tighter than 

 most houses would be. 



Plant lice are, as a rule, more easily 

 controlled than thrips, and it is prob- 

 able that the treatment just described 

 would prove effective against them 

 also. If any of the thrips are in the 

 egg stage, however, it is questionable 

 whether such would be destroyed in 

 this way, and it would be well to 

 watch carefully after such a treatment, 

 for a week or ten days, for young 

 thrips which may have hatched, and re- 

 peat the dose if any are found, four- 

 teen days after the first fumigation. 



White Fly. 



The white fly is more resistant than 

 plant lice, and probably than thrips, to 

 nicotine. Accordingly, hydrocyanic acid 

 gas is generally necessary for the con- 

 trol of this pest. It has been found, 

 however, that in many cases a fumi- 

 gation sufliciently strong to destroy 

 these insects in all stages is too strong 

 for the plants they are on. Usually, 

 when it is first noticed, all stages of 

 this pest are present together. Fumi- 

 gation with hydrocyanic acid gas, us- 

 ing from seven-thousandths to one- 

 hundredth of a gram of cyanide per 

 cubic foot (twenty-five-hundredths to 

 thirty-five-hundredths of an ounce per 

 1,000 cubic feet), according to the 

 tightness of the house, for three hours 

 after dark, will kill the adults and 

 most of the larvae, without injury to 

 the plants. Fourteen days later the 

 eggs will have hatched into larvse and 

 can be killed by a second treatment, 

 but the pupae which escaped the first 

 treatment will have turned into adults, 

 some of which, at least, will have laid 

 eggs. In order to get the remainder, 

 therefore, a third treatment, again 

 fourteen days later, will be necessary 

 to destroy the last of these pests. 



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

 at the Massachusetts Agricultural College, Am- 

 herst, Mass., read before the florists during 

 Farmers' Weelc at Amherst, continued from The 

 Ueview of May 2. 



Beyond these facts we know little in 

 detail. Two-hundredths of a gram of 

 cyanide per cubic foot (seven-tenths of 

 an ounce per 1,000 cubic feet) will kill 

 thrips, but in many cases at least is 

 dangerous to plants. Thus with the cu- 

 cumber, in experiments carried on at 

 the Massachusetts Agricultural Experi- 

 ment Station, one-third of an ounce per 

 1,000 cubic feet for forty minutes was 

 about as strong as was safe for the 

 plants, while in Maryland three-quar- 

 ters of an ounce for the same area, left 



The Kditor la pleased 

 i^hen a Reader 

 inresents Me Ideas 

 on any subject treated In 



fV/ls^lEt 



As experience Is the beet 

 teacher, so do -w 

 learn fastest by an 

 exchanee of experiences. 

 Many valuable points 

 are broucht out 

 by discussion. 



nood penmanship, spellincr and 

 grammar, though desirable, are not 

 necessary. Write as you would talk 

 when doing your best. 



WX SHAIX BK GLAD 

 TO HKAR FROM TOU 



all night, caused no injury. In such 

 cases it is probable that the difference 

 was at least in part due to a differ- 

 ence in the tightness of the houses 

 used for the experiments. 



Effectiveness and Safety. 



At the present time the following is 

 about as far as we can go in stating 

 the relative resistance of different in- 

 sects to fumigation: Plant lice, except 

 in the egg state, are probably the most 

 easily destroyed of greenhouse pests. 

 Next would come thrips and the white 

 fly, though here, too, the eggs are 

 noticeably more resistant than the 

 other stages, and probably at least a 

 second treatment after these hatch will 

 always be necessary. Mealy bugs 

 would perhaps come next in the list. 



followed by the scales and lastly by 

 the red spider, which seems to be par- 

 ticularly resistant to hydrocyanic acid 

 gas. In all cases the eggs are more re- 

 sistant than the other stages, and this 

 may be due to the extremely small 

 amount of oxygen required for devel- 

 opment in this stage, so that a long 

 exposure would be necessary for their 

 destruction. 



As regards the strength of gas dif- 

 ferent plants can stand without injury, 

 we are almost without information. 

 Various statements have been pub- 

 lished with reference to one kind or 

 another, but usually with no details. 

 Thus the Easter lily has been reported 

 as suffering no injury by exposure to 

 two ounces of cyanide over night, but 

 the temperature of the house, its hu- 

 midity, and whether the house was 

 tight or so loose that the gas had all 

 escaped after an hour or two, are all 

 unknown, though any one of these fac- 

 tors might make all the difference in 

 the world in the result. Comparing all 

 the data we have, however, it seems 

 probable that we should regard young 

 chrysanthemums, the sweet pea, core- 

 opsis, mignonette, carnation, asparagus 

 fern, pellaea, tradescantia and tomato as 

 among the more delicate plants, fumiga- 

 tion of which must be given with cau- 

 tion. How far this list should be ex- 

 tended is as yet unknown. 



Temperature and Humidity. 



The effect of temperature upon fumi- 

 gation is almost entirely unknown. A 

 few experiments along this line, made- 

 at the experiment station here, would 

 indicate that temperature is not an im- 

 portant factor, but that, on the whole, 

 a lower temperature ii^ preferable to a 

 higher one. ' 



The same appears to be true to some- 

 extent of humidity, though there is 

 some evidence to show that when the 

 atmosphere of the house is moist there 

 is more danger of injury than where 

 this is not the case. 



On the whole, the results of experi- 

 mental work seem to suggest that there 

 is more danger to plants fumigated for 

 a long time with a small amount of 

 gas, than to those exposed to a larger- 

 amount for a shorter period. Ulti- 

 mately it will probably be found that 

 somewhere between these two extremes 

 is an optimum exposure with a corre- 

 spondingly effective amount of gas, 

 though data on this point are at pres- 

 ent entirely lacking. 



Belation of Light to Safety. 



Finally we come to the question of 

 the relation of light to safety in fumi- 

 gation. Here, at last, we have at least 

 a little definite knowledge. Fumigation 

 with hydrocyanic acid gas cannot be 

 safely carried on during the daytime 

 and there is liable to be some injury 



