﻿DRY SUBSTITUTES FOE LIQUID LIME-SULPHUR 13 



DISCtrSSION OP FIELD EXPERIMENTS WITH DRY CALCITTM-SULPHURS 



The experiments already described show that when these dry 

 lime-sulphurs were used at dilutions from 12.5 to 15 pounds to 50 

 gallons of water the average control on hibernating scale was only 

 29.16 per cent. When the strength was increased to 25 or 27 pounds 

 the average control was increased to 54.68 per cent. In the same 

 series of tests standard liquid lime-sulphur gave an average control of 

 83.66 per cent. These figures show that the dry materials tested 

 did not give a control against hibernating scale which approximated 

 that obtained with liquid lime-sulphur, or one that could be considered 

 of very much practical value. 



If the efficiency of these dry substitutes is measured by the number 

 of young scales that settle on the new wood, the same lack of control 

 is found. On apple trees the weaker sprays showed an average of 2,409 

 scales of the first generation on each 80 linear inches of new wood 

 examined, or 30 scales to the inch. The stronger sprays gave an 

 average of 1,263.6 scales per 80 inches, or 15.8 per inch. These 

 treatments should be comparedwith liquid lime-sulphur which allowed 

 an average of 1.4 scales per inch to settle. 



The counts of second-generation scales on peach showed an average 

 of 8.19 scales per inch of new wood where the weaker sprays were 

 used, 5.61 for the stronger sprays, and 1.3 for liquid lime-sulphur. 



These experiments cover a variety of conditions, since they were 

 carried on in Indiana, Virginia, and Mississippi. In 1922 the orchards 

 treated were incrusted and the scale was increasing very rapidly, 

 whereas in 1923 orchards only moderately infested, in which the scale 

 was not increasing very rapidly, were used. Although the dry lime- 

 sulphurs, in all cases, show some effect on the scale, the apparent 

 control was never great enough to justify their being used as reme- 

 dies for the San Jose scale under general orchard conditions. 



S- A. Forbes has estimated {11, p. 54-9) that the theoretical number 

 of the progeny from one hibernating female San Jose scale might, 

 under ideal or optimum conditions, in one season, reach the aston- 

 ishing total of 32,791,472. If the actual increase under natural con- 

 ditions is even as low as 1 per cent of the theoretical it is still very 

 evident that a treatment which does not kill more than 50 per cent 

 or 60 per cent of the hibernating scales, and allows from three to six 

 scales to settle on each inch of the new wood, can not be considered 

 satisfactory, since it would not prevent an immediate reinfestation 

 and the resulting damage to the trees. 



EXPERIMENTS IN 1924 



The experiments conducted in 1924 were primarily for the purpose 

 of determining the relative value of the ingredients found by chem- 

 ical analysis to be present in the dry and liquid lime-sulphurs. 



Based on the analyses of more than 100 commercial lime-sulphur 



, . ,, 1 1 X- Pol ysulphide sulphur . , ^^ 



solutions the average molecular ratio -.y-.- /i • , , • is 4.68, 



^ rolysuiphuio calcium ' 



indicating a predominating percentage of the higher sulphide, CaSs, 

 whereas from the ansilyses of 38 samples of dry lime-sulphur the molecu- 

 lar ratio ti\-^^",/. ,' ' , • is 3.53, indicating that the polysul- 

 Polysulphide calcium " ^ -^ 



phides are mainly the lower sulpliidos, CaS^ and CaSg. 

 58254—261 3 



