WOUND DRESSINGS ON APPLE TREES 15 



WOUNDS TREATED WITH DRESSINGS NO. 540 AND NO. 541 PLUS 

 GASOLINE OR OTHER SOLVENTS 



Since it is sometimes difficult to provide warming facilities to melt 

 a thick wax dressing, such as No. 540 and No. 541, it is desirable to 

 know the effect of a solvent. When gasoline 6 was used as a solvent, 

 enough was added to make the dressings of the consistency of a thick 

 paint (see p. 5). At the end of the first season both No. 540 and No. 

 541 thinned with a solvent showed in general more extension or dying 

 and also less callus growth than the same dressings without solvents. 

 Other solvents used on parallel plots with gasoline were acetone, 

 Varsol, and Bayol. All the dressings in which these solvents were 

 used were more injurious than those containing gasoline. 



WOUNDS TREATED WITH WAX EMULSION AND PARAFFIN 



A wax emulsion was also used at most of the treatment dates. 

 Because callus formation was not so good and was more irregular than 

 where dressing No. 541 or shellac was used, results with this dressing 

 are not reported in detail. Paraffin was tried as a wound covering at 

 Hood River, Oreg. Wounds so treated made rapid callus growth, 

 but the callus seemed thin and abnormal and was susceptible to winter 

 injury. The action of paraffin on callus formation may be due to 

 modifying aeration and respiration or to the presence of some growth- 

 promoting substance. Experiments by Shear {12), which involved 

 treating wounds with growth-promoting substances, indicated that 

 callus formation may be accelerated by such substances. 



WOOLLY APPLE APHID DETERRENTS AND APHICIDES 

 IN RELATION TO PERENNIAL CANKER 



In the early stages of these experiments the idea prevailed that 

 infection by the perennial canker fungus occurred in fresh pruning 

 wounds or cut-out cankers and, therefore, that a wound dressing 

 containing a disinfectant should be effective in preventing canker 

 infection. Subsequent work (4) demonstrated that infection with 

 the perennial canker fungus takes place in new pruning wounds only 

 under very restricted conditions and that by far the most important 

 canker development in nature takes place in callused wounds that 

 have been weakened or injured by cold. In the Hood River Valley 

 and other localities in the Northwest, calluses on which woolly apple 

 aphids have been feeding are much more susceptible to winter injury 

 by low temperatures than calluses not infested with aphids. 



When this work was being carried on at Hood River, Oreg., the 

 woolly apple aphid infestation on the above-ground parts of apple 

 trees was very serious. The feeding of these aphids on wound callus 

 predisposed the callus to winter injury, which in turn made conditions 

 favorable for infection by the perennial canker fungus. At that time, 

 it seemed important to obtain information concerning the incorpora- 

 tion of an aphicide or an aphid deterrent in a wound dressing. 

 For this purpose the following substances were tried: Creosote, 



5 Commercial gasoline not containing tetraethyl lead. 



