No. 7. DEPARTMENT OF AGRICULTURE. 585 



blight, caused by Bacillus amylovorus, affecting the fruit spurs or 

 new twig growth or the bark of larger limbs and trunk or possibly 

 the crown region of the tree, and perhaps also two or three troubles, 

 caused by higher fungi, which may resemble bacterial blight super- 

 ficially in their effects. 



The story of bacterial blight is an old one with you, and I have 

 little that is new to bring either from my own work or the work 

 of others, ^Ve must keep constantly in mind the fundamental facts 

 about this disease of apple and pear and quince. It is constantly 

 present in most orchards. It is highly contagious. It is transferred 

 largely by insects, and gains entrance through wounds, however 

 slight, and exposed flower parts. It spreads rapidly and becomes 

 destructive when warm, moist weather conditions favor; this may 

 be at the time of flowering, with destruction of flowers, and later 

 of forming fruit, or it may be late in the season with little immed- 

 iate damage. It spreads downward in twigs, fruitspurs and water 

 sprouts, finally becoming established within the thick bark of large 

 limbs ; it may girdle these killing important parts of the tree ; and it 

 winters regularly in such cankers, thus starting new infection the 

 following season. 



Blight can be kept out of orchards, but it requires systematic, 

 persistent, thorough-going effort. Affected twigs and spurs must 

 be looked for regularly and frequently at dangerous periods, and 

 removed before the infection spreads to larger limbs, the removal 

 of which Avould entail greater loss. Trees should be kept clear of 

 useless water sprouts and on very susceptible varieties, fruit spurs 

 had best be confined to smaller limbs. In cutting aAvay affected 

 twigs, limbs, and bark canker areas, care must be taken to include 

 all possibly invaded material. In active lesions the bacteria push 

 constantly forward into new regions, and always exist beyond the 

 evidently dead portion. It is a good practice to cut twigs and limbs 

 a foot below apparently affected parts if possible, remembering 

 that if any part of the invaded tissue is left, the work has been for 

 naught. The greatest difficulty is in dealing with cankers on larger 

 limbs, and it is well worth while preventing their development by 

 promptly removing affected twigs and spurs before infection extends 

 to the parent limb. Sometimes these occur in crotches when it is 

 hard to get at them; and always there is little chance to cut away 

 much bark beyond the dead area. But all bark showing any dis- 

 coloration inside must be cut away if the work is to be successful. 

 In all of this removal work, disinfection of wounds and tools must 

 be carried out. Wound disinfection is placed first because of wounds 

 are clean cut their prompt disinfection will not only destroy bac- 

 teria immediately introduced from possibly infected tools, but will 

 offer continued protection for some time to come. If a sponge or 

 swab is carried, it is easy to touch every cut surface with the dis- 

 infectant, and to wipe the tools at frequent intervals. A number 

 of antiseptic substances might be used; probably the best is cor- 

 rosive sublimate in strength of 1 to 1000, or one ounce to seven or 

 eight gallons of water. Of course, the larger wounds should after- 

 wards be painted with thick lead and linseed oil paint. While it 

 is a safe precaution to collect and burn all infected trash, it is far 



