392 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 14 



DUST INSECTICIDES IN CALIFORNIA 



By E. O. EssiG, Univ. of California, Berkeley, Calif. 



Recent developments in the use of dust insecticides in California are 

 the outgrowth of some investigations and experiments on the walnut 

 aphis (Chromaphis juglandicola Kalt.) by Prof. R. E. Smith, of the Div- 

 ision of Plant Patholog}^ University of California, begun in 1914. Pro- 

 fessor Smith had been doing considerable experimental spraying of wal- 

 nuts for the control of walnut blight and it was in connection with this 

 disease that aphis control was also undertaken. The desirability of a 

 dust which could be quickly and cheaply applied was apparent, because 

 the well-known nicotine and soap sprays were almost prohibitive on 

 account of the great size of the trees. The first definite results were 

 obtained by impregnating finely pulverized kaolin with "Blackleaf 40". 

 For the walnut aphis a dust com.posed of 2% "Blackleaf 40" was found 

 to be thoroughly adequate. 



Orchard tests w^ere so thoroughly satisfactor\^ during the years follow- 

 ing 1916 that a great impetus was given to the study of dusts in general 

 with the results that rapid advance is being made along many new lines. 



The development of the so-called nicodust was made by Professor 

 Smith through the California Walnut Growers Spray Manufacturing 

 Company which manufactured the material in large quantities particu- 

 larly for members of the California Walnut Growers Association, but did 

 not neglect to develop a general trade in the insecticide. The namie 

 nicodust originally given the m.Lxture by Professor Smith has become so 

 general that it will probably always be used to designate any dry mate- 

 rial treated with a nicotine extract and is so usedinm.ost western articles 

 dealing with such materials. 



So great has been the interest in this material that it is now prepared 

 by at least four large insecticide manufactureres and the number is in- 

 creasing rapidly. Various combinations and mixtures of nicodust vnth 

 sulfur, the arsenic compounds, fungicides, etc. are also appearing in rapid 

 succession until the orchardist is faced with a serious problem in select- 

 ing the really efficient and less expensive article. At the present time 

 lime has practically replaced kaolin, because it liberates the volatile 

 nicotine m.ore readily and therefore gives better results. 



Many experim.ents were and are still being conducted by the manufac- 

 turers and others to determine the efficiency of nicodust and its various 

 com.binations for different insect pests and plant diseases. Professor 

 Smith did considerable along this line, particularly in the control of aphids 

 and the onion thrips. 



