4 CIRCULAR 65 6, U. S. DEPARTMENT OF AGRICULTURE 



asphalt, beeswax, pine gum, paraffin, Japanese wax, spermaceti, 

 cocoa butter, and rosin were used in combination with the following 

 carriers: Spray oils, castor oil, drying and nondrying fish oils, linseed 

 oil, petrolatum, transmission oil, hydrogenated fat, cottonseed oil, 

 rapeseed oil, crude petroleum, and glycerin. These were applied 

 while warm or thinned with gasoline, kerosene, turpentine, ethyl or 

 methyl alcohol, acetone, Varsol, 3 and Bayol. 3 



Of the various materials tried, thfe best dressings were made by a 

 combination of rosin and fish oil. Such a dressing was also used for 

 the incorporation of the following substances expected to have disin- 

 fecting properties: Copper sulfate, bordeaux mixture, sulfur, paris 

 green, copper soap, and copper resinate. Of the large number of 

 materials used in one way or another, copper soap seemed to be the 

 most promising to combine with a wax 4 containing rosin and oil. 



Other chemicals not miscible with the previously mentioned wax- 

 like dressing were used in water and kaolin or in a water emulsion. 

 The following were so used: Mercuric cyanide, mercuric chloride, 

 sodium chromate, zinc chloride, cresylic acid, picric acid, and creo- 

 sote. 



More than 500 combinations of the various ingredients were made, 

 many of which were tested by application to pruning wounds and 

 wounds resulting from excision of cankers. Others were discarded 

 without testing because of evident unsuitableness. Most of the 

 substances had decided draw-backs. Some were so thick that they 

 prevented proper aeration and drying of exuded sap and thus resulted 

 in water blistering, a condition also noted by Marshall (10). Other 

 dressings soon crumbled off under the influence of weathering agents. 

 Still others, such as oil and lead paint, made a hard, continuous 

 covering, and callus growth soon produced cracks that provided 

 shelter for the woolly apple aphid (Eriosoma lanigerum (Hausm.)). 

 The application of such substances as paraffin resulted in callus growth 

 that was abnormally susceptible to winter injury. 



Many coverings containing an active disinfectant were abandoned 

 because they killed the tissues surrounding the wound. In some 

 cases the solvent that was used caused killing, particularly on fresh 

 wounds. Sometimes uncombined oils caused injury, especially when 

 applied during the autumn. 



Two of the large number of dressings tested in the Hood River 

 Valley, Oreg., No. 540 and No. 541, seemed most promising and were 

 later used at Arlington Experiment Farm, Arlington, Va., in compar- 

 ison with other dressings, in the study of callus behavior. 



Dressing No. 540, containing a disinfectant, was made by the fol- 

 lowing formula by weight: 



Rosin (H or I grade) 7 parts 



Sardine oil 3 parts 



Copper soap 3 parts 



Dressing No. 541, which appeared to be the best of all wax-type 

 dressings, differed from No. 540 mainly in the omission of the copper 

 soap. It contained by weight: 



Rosin * 8 parts 



Sardine oil 3 parts 



3 Supplied for test by the courtesy of the manufacturer. 



4 In chemical literature, wax is used to designate a group of substances having a definite chemical struc- 

 ture, the most familiar being beeswax. In this circular, however, the term "wax" is used to designate 

 compounds having certain waxlike physical properties, but not necessarily conforming to the chemical 

 definition of a wax. 



