BETTER FRUIT 



Pioneer Horticultural Journal of the Pacific Northwest 



Entered as second-class matter April 22, 1918, at the Postoffice at Portland, Oregon, under act 



of Congress of March 3, 1879 



Volume XV 



Portland, Oregon, June, 192 1 



Number 12 



Use of Dust Sprays in California 



By W. L. Howard, Professor of Pomology, University of California. In Charge Deciduous Fruit Station, Mountain View, California 



DUST sprays, used both as fungi- 

 cides and insecticides, have been 

 in general use in California for 

 many years. Dry sulphur has always 

 been the standard remedy against mil- 

 dew in grapes, and since the vineyard 

 business in California has always been 

 one of our most important agricultural 

 industries, enormous quantities of sul- 

 phur have been used in dusting the vines. 

 In no other instance, however, has a dry 

 spray proved of practical importance 

 in California as a fungicide. There has 

 never been any serious effort to use 

 dTy sprays against diseases of tree 

 fruits, except possibly to employ dry 

 sulphur against the mildew in apples, 

 and this was always a failure. Wet 

 sprays, it may then be said, are now 

 almost exclusively employed for con- 

 trolling diseases. 



In striking contrast with disease con- 

 trol, splendid success has attended the 

 use of dry sprays against certain in- 

 sects. One of the first marked success- 

 es in this direction "was the use of sul- 

 phur dust against red spider on almond, 

 peach and prune trees. The dust is ap- 

 plied, usually by means of a hand dust- 

 ing outfit, after the insects appear in 

 midsummer. It is believed that the kill- 

 ing principle of the spray depends upon 

 the slow volitalization of the sulphur 

 under the heat of the sun, and that it 

 is these slowly liberated fumes that 

 kill the mites. 



During the past year or two, another 

 long step has been taken in the use of 

 dust sprays by the discovery of a new 

 insecticide which can be used as a dry 

 spray. The new dusting material con- 

 sists of a carrier made of kaolin clay, 

 which easily reduces to an almost im- 

 palpable powder, to which is added 

 specific quantities of nicotine sulphate 

 (Black Leaf 40). This material, the or- 

 iginal brand of which is known as nico- 

 dust, is now available in different 

 strengths, namely twe per cent, five 

 per cent and ten per cent. This spray- 

 ing material was designed by Prof. R. 

 E. Smith, head of the Division of Plant 

 Pathology of the College of Agriculture 



of the University of California, as a 

 remedy against leaf aphis of walnuts. 

 It had never before been possible to 

 control this insect on walnut trees, 

 mainly for the reason that the trees 

 were too large to be successfully 

 sprayed w T ith liquids. It often required 

 hours to spray a single tree properly 

 with a liquid, and then the results were 



Prof. E. O. Essig has secured some 

 splendid results during the present sea- 

 son in the control of the rosy apple 

 aphis by dusting with what is known 

 as the double nicodust, which contains 

 5.9 per cent of nicotine sulphate. This 

 corresponds very closely to the so-called 

 ten per cent nicodust of last year. The 

 dust seems to penetrate the clumps of 



Applying Nicodust in the Orchard 



far from satisfactory. The job may 

 now to be done with two per cent nico- 

 dust in a few minutes, and obtains a 

 very satisfactory slaughter of the in- 

 sects. 



During the season of 1920 the De- 

 ciduous Fruit Station of the University 

 of California found that a five per cent 

 nicodust could be very successfully used 

 in controlling thrips on prunes and 

 pears, as well as on nursery stock. Ow- 

 ing to the fact that nicodust kills by the 

 rather rapid liberation of the nicotine 

 fumes, it is necessary to apply the ma- 

 terial to the trees during the warm part 

 of the day, under California conditions, 

 as the nights and early mornings 

 throughout the spring and most of the 

 summer are apt to be very cool. 



leaves that have been curled by the 

 work of the aphis much better than 

 liquid sprays, and the kill of the insects 

 has been very gratifying. The same 

 dust seems to penetrate the clumbs of 

 the mealy plum plant louse, with very 

 promising results, even after the leaves 

 have been badly curled. 



Strange enough, the nicotine dust 

 has not been a success against the red 

 spider. This may possibly be due to the 

 fact that the fumes are liberated too 

 rapidly. Apparently after about three 

 hours all of the nicotine vapors have 

 become completely dissipated, whereas 

 sulphur fumes are liberated more grad- 

 ually and continue for days. 



Arsenical sprays in dust form, as 

 well as certain fungicidal sprays, are 



