1921 ENTOMOLOGICAL SOCIETY. 65 



Tobacco Dust Treatment. The results secured by Sasscer and Borden with 

 tobacco dust were, later on, confirmed by laboratory experiments at Vineland 

 Station. These experiments furnished us not only with positive evidence that a 

 coat of tobacco dust would kill the full-grown larva? which dropped from the plants, 

 but also that the nicotine absorbed by the soil from the dust would destroy the 

 midge pupa? and larva? in the soil. In short, our laboratory tests indicated that 

 in combating the midge it was not necessary to supplement the soil treatment by 

 nightly fumigation with nicotine. In view of the cost of nightly fumigation the 

 importance of this discovery is apparent. 



For various reasons we were unable to give the tobacco dust remedy a trial 

 under commercial conditions until this year, when it was tried out in four 

 greenhouses. 



Olfield's Greenhouses. Messrs. Olfield and Sons' establishment at Grimsby, 

 with 250,000 sq. ft. of glass, and containing some 85,000 rose plants, was very 

 heavily infested with midge in 1919, when the insect caused a loss of approximately 

 $12,000. At the time operations were commenced against the midge practically 

 one hundred per cent, of the young growth of all the susceptible varieties was 

 infested. 



During the second week of August the fallen leaves on the beds were removed 

 and the soil was tamped in order to break up lumps and to make the surface as 

 smooth as possible. The beds were then thoroughly drenched with water, and a coat 

 of tobacco dust one-fourth to one-half inch thick was applied, great care being 

 taken to cover all parts of the beds (35 tons of dust used). As an additional 

 precaution all the walks were sprayed with kerosene emulsion, in order to kill any 

 larva? which might have fallen from the plants to the walks. Eor two weeks after 

 the dust was applied the foliage was syringed occasion ally, but the beds were not 

 actually watered. Our object in withholding the water was to prevent the washing 

 of nicotine out of the dust until all the larva? present on the plants had dropped to 

 the soil. 



Results. The establishment consists of three ridge and furrow houses, which, 

 for the sake of convenience may be referred to as Nos. 1, 2, and 3. In houses 1 

 and 3 absolutely no larva?, with the exception of some present on the plants for a 

 short time after treatment, have been found since the application of the remedy. 

 In No. 2 a few infested Ophelia buds * were discovered on September 11th. All 

 these buds were immediately destroyed, and the section in which they were dis- 

 covered was promptly treated again with tobacco dust. Since this second treatment 

 no midge has been .seen up to the present. 



It is of interest to note that the application of kerosene emulsion to the walks 

 caused a very small percentage of the foliage of White Killarney to drop. The 

 plants, however, were not injured to any appreciable extent. 



Dale Estate. The Midge, introduced into this large plant in 1919, had 

 established itself in three houses, and was causing serious loss. Early in July of 

 the present year, from 300 to 400 infested buds were pinched off and destroyed 

 daily in the worst affected section. 



Operations were commenced against the midge about mid July. The beds 

 were cleaned up, tamped, and were then carefully covered with tobacco dust, (38 

 tons used). At the same time the sidewalks were sprayed with kerosene emulsion. 



* We have good reason to believe that this infestation came from affected buds 

 thrown under the benches by a careless grower. 



