WOUND DRESSINGS ON APPLE TREES 17 



Shellac gave less killing and more callus formation than any of the 

 other dressings tried. Where a heavier covering than shellac is 

 desired, dressing No. 541, which is composed of rosin and fish oil 

 and gave good results, is suggested. The waxlike dressings gave 

 better healing when applied warm than when thinned with 

 the solvent, gasoline. Injury from the thinner was less in the spring 

 treatments than in those of the other seasons. The injury from 

 the thinner was not great enough to discourage its use for spring 

 treatments, but it is inadvisable to use it for winter treatments. 



If protection from woolly apple aphid about pruning wound calluses 

 is desired, dressing No. 541, which gave better results than any other 

 dressing, may be used. It should be applied as late as possible 

 before the wound callus is infested. It usually afforded protection 

 from woolly apple aphid throughout the summer. 



In case shellac or rosin and fish oil cannot be obtained under exist- 

 ing priorities the orchardist should be careful what treatment he 

 substitutes. The work reported emphasizes the injurious effect on 

 wounds on apple trees of a wound dressing that is only slightly toxic. 

 Before applying a disinfecting wound dressing, which will probably 

 enlarge the wound, one should have information as to whether or 

 not the disinfectant will retain its activity long enough to be useful 

 and also whether the hazard of possible heart rot injury would be 

 greater than the known hazard of wound-dressing injury. 



SUMMARY 



The most promising of a large number of wound dressings were 

 tested on the limbs of mature apple trees at Hood River, Oreg., and 

 at Arlington Experiment Farm, Arlington, Va. Internodal or side 

 wounds 25 millimeters in diameter made at monthly intervals for 2 

 years were treated with two waxlike dressings in comparison with white 

 lead and linseed oil, shellac, and no treatment. One waxlike dressing 

 (No. 541) contained eight parts by weight of rosin and three parts of 

 sardine oil; the other (No. 540) was similar except that it contained 

 copper soap in addition. 



More rapid healing took place in the transverse diameter; in the 

 longitudinal diameter the wounds enlarged by dying even where the 

 best dressings were used. Even at the end of the second growing 

 season the longitudinal diameters of the wounds were larger than at 

 the beginning. 



Wounds made in June or later produced little or no callus, in which 

 cases enlargement due to dying took place in the transverse as well as 

 in the longitudinal diameter. The longitudinal extension of wounds 

 made in winter was in general greater than that of those made in the 

 spring. The slightly injurious dressings caused less killing when 

 applied in the spring than at any other time of the year. 



Shellac gave more callus formation and less dying or longitudinal 

 extension of the wound than any other dressing used. Dressing No. 

 541 gave better healing in general than white lead and linseed oil or 

 dressing No. 540. The untreated wounds gave better healing in gen- 

 eral than those treated with white lead and linseed oil, but poorer 

 than those treated with shellac. 



When protection from the woolly apple aphid on wound callus is 

 desired, dressing No. 541 is suggested, as the best results were obtained 

 with it. 



