CUTTING OR SCRAPING PEAR BLIGHT 267 



the tree by slow degrees, due to the destruction of the inner bark of the 

 trunk or main roots. In such cases the leaves of affected trees take on a 

 peculiar bronzy reddish coloration in the fall, which is quite characteristic 

 to the experienced eye. 



From the "hold-over" blight in the trunks and large limbs an infectious 

 sap exudes when growth starts in the spring, which sap contains myriads 

 of the blight organisms. This sap is attractive to insects, which, in feeding 

 upon it, get the blight bacteria upon their bodies and mouth parts, and 

 transfer them to the blossoms or green shoots of other trees, thus spread- 

 ing the infection. 



Looking for Blight. The time to see blight best is while the 

 tree is in leaf. Discovery and cutting out should be in mind all 

 summer especially should thorough work be done in the autumn. 

 The leaves are still hanging on blighted twigs; trees are least sus- 

 ceptible to reinfection from careless cutting because they are practi- 

 cally dormant ; insects are not so numerous, and the rain is not yet 

 soaking newly cut surfaces with drippings from other new cuts. 

 It is easy to get around the orchard, and mud does not hinder fol- 

 lowing root blight. 



Cutting Out Blight. Cuts should usually be made about a foot 

 below visible appearances of blight on the bark; (2) tools are dis- 

 infected before making the cut; (3) the wound immediately after 

 the cutting is sponged with a disinfectant of which the one chiefly 

 used is one part of corrosive sublimate to 1000 parts of water by 

 weight; which is one ordinary tablet of corrosive to one pint of 

 water. Dr. F. C. Reimer of Oregon, the noted pear expert, recom- 

 mends cyanide of mercury to disinfect cuts and wounds instead 

 of corrosive sublimate 1 gram of pure cyanide of mercury to 500 

 grams of water (about one pint). Large cut surfaces should be 

 subsequently brushed or sprayed with Bordeaux mixture or lime- 

 sulphur wash. 



Scraping Instead of Cutting. In 1921 a new method of checking 

 the progress of the blight downward is being employed in the treat- 

 ment of larger branches and trunk. It is described as follows :* 



The new method of control consists in the scraping of the outer layer 

 of bark on all infected areas, and it is very essential to scrape for insur- 

 ance at least eight to ten inches above and below all visible signs of blight. 

 The scraped area is then painted or saturated with a solution of cyanide of 

 mercury (1 to 500). On trunk infections it is found best to scrape a little 

 closer to the cambium or growing layer of bark. It is found that the 

 cyanide solution does not penetrate to the cambium if too much outer 

 bark is left. On working on large areas disinfecting should be done sev- 

 eral times during the operation because the surface of the bark becomes 

 dry and the solution cannot penetrate to the inner blight. If a mud paste 

 of cyanide solution and earth is put on the scraped area it helps to keep 

 the wound damp for some time and the cyanide effective for a longer 

 period. Bichloride solution, 1 to 1000, is better to use to disinfect tools. 

 The bichloride solution and cyanide solution (1 to 500) may be mixed in 

 the same bottle for convenience. 



Pear Scab. The scab fungus which seriously affects some 

 varieties, and notably the Winter Nelis, is identical with the scab 

 of the apple and will be mentioned in the chapter on tree disease. 



*E. I. Power in Pacific Rural Press, March 26, 1921. 



