April, '211 



headlee: dusting for insect control 



217 



use of the dust was, at least, as good as that obtained by liquid sprays, 

 the writer has given considerable thought to the possible reason for the 

 wide difference in the findings as reported by Professor Whetzel and the 

 facts as derived from the New Jersey experience. 



The fact that the codling moth in Nova Scotia, New York and 

 Michigan shows either one brood or one and a partial second may have a 

 good deal to do with the apparently better results obtained with dust 

 in these areas, because the period during which the fruit must be pro- 

 tected is scarcely more than one-half of the time during which the fruit 

 must be protected in New Jersey where two full broods of that insect 

 are developed, but this will not hold in making comparisons of results 

 obtained in Illinois, for in that state there are also two full broods of the 

 codling moth. 



RAINMLLi 

 INCHES 

 1920 



3 4 



6A 



CURCULIO I 



/5^0 2b 30 5 10 15 20 25 30 4 9 14 19 24 29 4 9 14 19 24 29 3 8 13 1825 28 2 7/2 17 22 27 30 



APRIL r^lAY JUNE JULY AUGUST SEPTEHBEf? 



Fig. 4. Chart showing relation between rainfall, the occurrence of the codling 

 moth and curculio and the time of spraying. 



In Illinois, however, the normal annual rainfall is about 10 inches less 

 than it is in New Jersey and theoretically the washing to which the dust 

 applications would be subjected in that state would be materially less 

 than that to which they would be subjected in New Jersey. The total 

 rainfall in any year, or in any month is not a really trustworthy guide to 

 the effect of the same upon the efficiency of dust applied mixtures, 

 except insofar as the same indicates that the distribution during the 

 dusting period is such as promptly to wash off the applications. In 

 studying the effects of rainfall it is, therefore, necessary to study the 

 distribution of daily precipitation during the periods when the dust 

 must protect the fruit from the attacks of the codling moth. 



Such a study has been made under New Jersey conditions for the 

 year 1920. The season started late that year and the emergence of 

 the first brood of moths and the entrance by the larvae covered materially 

 -shorter periods than in 1919. An average of 2.8 pounds of dust were 



