﻿4 BULLETIN 1371, U. S. DEPARTMENT OF AGEICULTURE 



The Texas station in 1920 (24, p. 7) summarizes the results of 

 tests made with a sodium and a calcium-sulphur and a commercial 

 liquid lime-sulphur as follows : 



The fact that infestation increased heavily on all the trees in the check rows 

 while at the same time there was nearly perfect control in the case of the sprayed 

 trees, shows that all three materials were very effective in controlling the San 

 Jose scale under the conditions of this experiment. So far as we could determine, 

 there was very little if any difference in the effectiveness of the three materials. 



It is realized, of course, that this is only a preliminary experiment and that 

 further tests should be made with such mixtures before final recommendations 

 can be made. 



Numerous experiments with dry sulphur preparations are reported 

 by the Washington station {17 ; 18, p. 21) and the conclusions are 

 drawn that in certain parts of the State none of the sulphur sprays are 

 effective against the San Jose scale. 



In the April, 1924, issue of the Journal of Economic Entomology 

 {8, p. 288-289), J. J. Davis, of Purdue University, reports a large 

 series of tests made with various preparations against the San Jose 

 scale, and says: 



Results. — We have concluded from these tests and many scattered observa- 

 tions, that the dry lime-sulphur is inefficient against the San Jose scale as it occurs 

 at the present time in southern Indiana when used at label strength. The liquid 

 concentrate proved ineffective under the conditions which have prevailed in 

 southern Indiana the past few years. These results are corroborated by results 

 secured where the scale could not be checked even when 1-6 strengths were 

 used thoroughly. Even with a 90 per cent kill, the 10 per cent live scales on 

 moderately or heavily infested trees are able to increase and encrust a vigorous 

 tree by fall. The dry lime-sulphur when used at twice label strength was about 

 equal in effectiveness to the liquid concentrate. 



The lack of agreement in the conclusions reached by the investi- 

 gators quoted above may be explained in several ways : 



(1) The results were taken in many different ways and, in some 

 cases, the methods used apparently do not correctly represent the 

 effect of the treatment on the hibernating scale. 



(2) These experiments cover a period of six years, and it is gener- 

 ally recognized by entomologists that the virility of this scale in a given 

 locality may vary greatly in the course of several years, and, more- 

 over, some of these tests were made when the vitality of the scale was 

 very low. This has been well shown in Arkansas {3) where, prior to 

 1918, the scale had been kept in check by one dormant treatment 

 with liquid lime-sulphur. From 1919 to 1922 this pest became so 

 virulent that liquid lime-sulphur could no longer be rehed on, even 

 when two applications at greatly increased strengths were used. That 

 this was not the result of faulty spraying is shown by experiments of 

 the Bureau of Entomology at Bentonville, Ark., in 1921 and 1922. 



(3) It is also a well-established fact that the vitality of this species 

 of scale varies with the locality, and some of these experiments were 

 made in sections where the scale is not difficult to control. This 

 regional variation in resistance has been demonstrated by the work 

 of A. L. Melander (19) in Washington. 



(4) In many cases only the percentage of dead or Uving scale is 

 given and such results are very misleading if the number of dead 

 scales in the untreated plats, or checks, is not taken into considera- 

 tion.^ 



* See "Percentage of control," p. 6. 



