374 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 12 



cent were killed with concentrated lime-sulfur, 1-9 (see Charts II 

 and V). 



Dry lime-sulfur may be secured in two forms, a coarse powder which 

 is recommended for liquid spraying and a finely ground powder which 

 is suitable for dusting. The two forms behave differently when dis- 

 solved in water. Using amounts (thoroughly dried) equivalent to 14 

 pounds to 50 gallons of water only 65 to 67 per cent of the coarse prod- 

 uct dissolved in water in thirty minutes (thoroughly agitated) while 

 88 per cent of the fine powder dissolved under the same conditions. 

 In other tests similar to the above, except for the fact that the residue 

 in the filter was thoroughly washed, 74.2 per cent of the coarse form 

 dissolved while 90.3 per cent of the fine powder dissolved. The in- 

 soluble character of dry lime-sulfur, particularly the coarse form, is 

 undoubtedly objectional. To be most effective in spreading and as a 

 contact insecticide all the lime-sulfur should be soluble. A chemical 

 analysis of dry lime-sulfur shows approximately 55 per cent sulfur in 

 the dry product. When this product is used at the recommended 

 winter strength, 14 pounds to 50 gallons of water, figures show that 

 the spray, as it goes to the tree, contains approximately 50 per cent as 

 much sulfur per gallon as the recommended liquid lime-sulfur 1-9. 



The poor soluble character of dry lime-sulfur and the low sulfur 

 content of the recommended winter strength probably explains its 

 low efficiency in killing aphid eggs when compared with the recom- 

 mended winter strength of concentrated Uquid lime-sulfur. The sol- 

 uble character of the dry lime-sulfur is undoubtedly important for 

 the superior efficiency of the higher soluble dust form over the lower 

 soluble coarse form is clearly illustrated in Chart II, lines e, f, and g 

 (e = coarse lime-sulfur, 15 lbs. to 50 gals.; f = coarse dry lime-sulfur, 

 20 lbs. to 50 gals.; g = dust form dry lime-sulfur, 15 lbs. to 50 gals.). 

 Lines f and g approximately coincide and are considerably above line e. 

 This indicates that 20 pounds to 50 gallons of the coarse dry lime- 

 sulfur nearly equals the killing efficiency of 15 pounds to 50 gallons 

 of the dust form. 



A few dusting experiments (eggs of A. avence on March 7, 1919) 

 were tried with dry lime-sulfur (dust form) alone, hydrated lime alone 

 and a combination of one part dry lime-sulfur and one part hydrated 

 lime. The twigs were thoroughly covered and then placed out-of- 

 doors (as in other experiments). The eggs coated with dry lime- 

 sulfur showed a 28 per cent hatch; with hydrated lime, a 48 per cent 

 hatch, and with a combination of dry lime-sulfur and hydrated lime, 

 a 30 per cent hatch. The results of these few dusting experiments 

 indicate that the efficiency of dry lime-sulfur applied as a dust is con- 

 siderably less than when the dry lime-sulfur (dust form, 15 pounds to 

 50 gallons) is applied as a liquid spray. 



