20 Letters on the Diseases of Plants. 



III. Diseases of the Apple. 



1. Bitter Pit of the Apple. 



I MENTION this disease only to state that Mr. Eobinson, of Ashfield, at my 

 suggestion, has undertaken some experiments in order to find out if possible 

 whether this disease is transmitted by grafting, as I strongly suspect it 

 is. The results will be made known in due time. I think it will be no 

 breach of confidence to mention that experiments conducted by officers of 

 the Victorian Department of Agriculture are believed to show that this 

 disease cannot be alleviated by any kind of manure. 



2. Canker. 



The common and wide-spread diseases of the bark of trees known under 

 the general name of canker continue to trouble our orchardists as of old. 

 A few words suggested by the nature of the specimens and inquiries I have 

 received during the last few months may therefore be of service. 



The cause of most canker spots is external. Frost, 

 sun, hail, insects, or violent winds first of all injure 

 the bark, and then some parasitic or semi-parasitic 

 fungus attacks the wound thus made and increases 

 the "sore " faster than the bark can produce "healing" 

 tissue. The process goes on from bad to worse until, 

 in some cases, it seems as if there were no limit to 

 the consequent " sore " or excrescence. I have seen 

 such deformities a yard or more in diameter. The 

 disease is generally long drawn out, and in the case of 

 fruit-trees is particularly disheartening when severe. 

 Among fruit-trees, apple-trees are probably more 

 _,. „„ ,, , 11, subiect to canker than any others, though even they 



Fig. 20.— Canker on 11 limb of •> i • , < -j ji .' i, ^ \ 



apple. The disease appears are less suDJect to it than some timber trces. Asa 



fated brownish ^Hsteis/" matter of fact, nearly all the specimens of canker 



a,rranged transversely on the recently sent to this Department from the orchardists 



^^^' of the Colony are from apple-trees. Those who are 



curious concerning the nature of the fungi causing canker may find some 



satisfaction in studying the adjacent illustration, which was prepared from 



some diseased material sent me recently, and when they have done so will 



readily understand why the following recommendations were made. 



Semedies. 



1. Prune off or cut out the worst cases, and then apply grafting wax to 

 the freshly-made cut. Use sharp tools and do not cut sparingly. If you do 

 not remove all the diseased bark, the disease will remain and continue to 

 spread. Cut away all the bark that appears in the least swollen, discoloured, 

 or in any way unhealthy. Burn the cuttings. 



2. As soon as you can find out the original cause of the wounds remove it. 

 If it is the sun scalding the bark, prune the trees so as to cause the foliage 

 to shade the limbs and trunks more completely ; protect the trunks of young 

 trees from the sun by some artificial means if necessary. Provide wind- 

 breaks. Eemove any superfluous old bark, the scales of which may harbor 

 insects. 



