22 BULLETIN 712^ U. S. DEPARTMENT OF AGRICULTURE. 



is deposited when they decompose. However, it is certain that such 

 deposits of sulphur on healthy parts act in a protective manner 

 against potential infections. This being true, the advantages of 

 lime- sulphur solution are at once apparent, for not only does it 

 exert an immediate effect against existing infections, but by its de- 

 position over healthy parts free sulphur is soon made available and 

 distributed where protection is needed. 



It was found that colloidal sulphur possessed greater spreading 

 power than any other material tested. The uniformly excellent con- 

 trol established by its use is doubtless to be traced to this fact. It 

 appears that this material combines the most desired elements for 

 control, since it not only possesses excellent spreading qualities and 

 thereby deposits a very uniform coating of almost ultramicroscopic 

 sulphur particles to form a protective coating over healthy parts, 

 but at the same time it possesses in its excess lime-sulphur solution 

 sufficient causticity to produce an immediate effect on the fungous 

 mycelium and conidia. With the exercise of intelligent precau- 

 tions in its preparation there would doubtless be no reason for not 

 advocating its use on a commercial scale in general orchard practice, 

 especially where mildew infection is severe. However, since good 

 results attend the use of commercial lime-sulphur solution it is doubt- 

 ful whether many orchardists would go to the trouble of making the 

 colloidal sulphur. 



With the iron-sulphid sprays, the finely ground sulphur materials, 

 and the sodium-sulphur materials, from one-fourth to one-third more 

 spray material was required to cover the same surface with an effi- 

 ciency approximating that of either colloidal sulphur or lime-sulphur 

 solution. This apparently was due largely to the greater surface 

 tension and interfacial tension of these materials, giving them less 

 ability to wet the foliage and twigs, especially when covered with 

 mildew. This also resulted in lessened spreading power, and conse- 

 quently many places inaccessible to the direct force of the spray 

 when applied were not reached and remained unprotected. The 

 addition of soap, when not chemically incompatible, would increase 

 the spreading power and the value of such sprays. The poorer 

 results obtained from the use of these spray- were also partly due 

 to their lower concentration of active fungicidal ingredients. 



Bordeaux mixture, if combined with soap, spreads very readily, 

 but it proved objectionable in the climate of the Wenatchee Valley 

 because of the pale fruit color developed under the heavy spray coat- 

 ing. Black Ben Davis apples sprayed with Bordeaux mixture failed 

 to develop more than 50 per cent of the normal red color of this 

 variety and were discriminated against on the market on this account. 

 In the Wenatchee Valley there are no rains to wash off the spray 

 coating, and fruit sprayed with Bordeaux mixture in July still 



