14 



SCIENTIFIC AGRICULTURE 



January, 1921. 



Dusts and Dusting for Insect and Fungus Control 



By G. E. SANDERS and A. KELSALL, 



Insecticide Investigations, Entomological Branch, 



Ottawa. 



PART 1.— THE PRESENT STATUS OF DUSTING. 



A paper by Prof. II. H. Whetzel, Plant Patholo- 

 gist, Cornell tlniversity, entitled "The Present Status 

 of Dusting," was presented before the New York 

 State Horticultural Society on January 14th, 1920. 

 This paper contained a concise account of the problem 

 spray versus dust, and a close analysis of the published 

 experimental data of the last eight years. Inasmuch 

 as the conclusions drawn are in accord with the ex- 

 perience of many progressive men in Canada, the 

 writers feel that they will not be guilty of unnecessary 

 duplication in submitting an article of similar char- 

 acter dealing more particularly with Canadian condi- 

 tions, though utilizing several of the tables compiled 

 by Prof. Whetzel. 



Insects and fungi have undoubtedly troubled, culti- 

 vators from the time when plants were first grown, and 

 probably various materials and decoctions, both liquid 

 and solid, were thrown upon plants for purposes of 

 disease suppression as the cultivation of plants at- 

 tracted attention. Probably early records could be ob- 

 tained if sought for, but readily available records of 

 the eighteenth century show the use of sprays such as 

 lime-wash, tobacco water, sea water, and dusts such 

 as sulphur, powdered quicklime and soot. Our modern 

 conceptions of combined insecticides and fungicides 

 orginate from two distinct sources, the first milestone 

 in insecticides being the development of Paris green 

 in America between the years 1860 and 1870 for com- 

 batting potato beetles; and the first milestone in fun- 

 gicides being the development of materials for com- 

 batting diseases of the grape in France during the 

 latter half of the nineteenth century. It is very notable 

 that from 1860 to about 1885 insecticides and fungi- 

 cides were, for the most part, applied as dusts. In 

 America, Paris Green was diluted with flour, plaster, 

 or ashes and dusted on the foliage, and though in 

 some cases it was mixed with water and applied with 

 a syringe, the great bulk was used as a dust. In 

 France, sulphur was dusted on the vines to control the 

 European powdery mildew. The change came about 

 1882 following the introduction into France of the 

 American downy mildew. It was soon apparent that 

 sulphur would not control this mildew, and this fact 

 led to the epoch-making investigations of Millardet 

 and Gayon culminating in the discovery of Bordeaux 

 mixture. Bordeaux controlled the downy mildew read- 

 ily and trials soon showed that it controlled many other 

 diseases also, so that its use spread to all countries 

 and suitable machinery was developed for applying it. 

 It proved impossible to produce a good grade of Bor- 

 deaux mixture in dry form so that the practice of 

 spraying with liquid increased and dusting declined. 

 Consequently progress in the production of spraying 

 machinery was rapid while corresponding improve- 

 ments in dusting apparatus were not made. Thus the 

 discovery of Bordeaux mixture was in no small measure 

 responsible for the advancement of spraying and the 

 decline of dusting. 



But from the very beginning it was recognized that 

 dusting possessed several distinct advantages. No 

 person was more decidedly aware of this than Millar- 

 det. Coincident with his Bordeaux mixture investiga- 

 tions, he endeavored to produce similar copper com- 

 pounds in dry form for dust purposes. Most of these 

 entailed much labor in making, or did not possess ne- 

 cessary adhesive qualities, or were harmful to foliage. 

 It is interesting to note that of the many powders he 

 tried was one which contained anhydrous copper sul- 

 phate and air-slaked lime, and it is reported that he 

 obtained the best results with this material. It is un- 

 fortunate that hydrated lime was unknown at that 

 time, at least as a commercial product, for had Millar- 

 det had access to hydrated lime it is not improliable 

 that the whole procedure of disease control would 

 have been materially altered. As it was, Millardet 

 failed to produce a satisfactory dust. 



Consequently from about 1885 the standard and ac- 

 cepted way of applying insecticides and fungicides was 

 a.s a spray. But during the intervening years, a 

 gradual revolution took place in all agricultural opera- 

 tions, a revolution whereby one man did the former 

 work of two men, a revolution brought about by the 

 one thing, namely machinery. It became cheaper to 

 do a maximum amount of work with machinery and a 

 minimum amount with manual labor. It was impossible 

 for this shifting of economic conditions to be without 

 effect upon the operation of spraying. Large areas had 

 to be covered in a short time with as little manual 

 labor as possible, and this condition brought about a 

 reconsideration of the problems of dusting. 



The revival of dusting might be said to commence 

 about 1912, and since that time considerable progress 

 has been uuide in improved dusting machinery and in 

 our knowledge of dusting materials. The present time 

 therefore would seem very opportune for an inquiry 

 into tlie present status of dusting. 



Advantages of Dust over Spray. 



The advantages of dusting ovei' si)rayiiig liave been 

 reiterated in many articles, and have been generally 

 recognized and appreciated by all familiar with the 

 subject. The.y may be stated briefly as follows: 



1. — Greater speed in application. 



A dusting outfit is capable of treating from five to 

 ten times as much orchard as a .spraying outfit in a 

 given time. 



2. — More suitable timing of applications. 



Owing to the rapidity of application the grower can 

 time his applications to suit better the weather and 

 the stage of the fruit. 



3. — Less waste time. 



Dusting operations should be done during weather 

 unfit for most agricultural field operations, such as 

 immediatel.y after a rain or very early in the morning, 

 while spraying operations require the best of 

 weather. 



