1644 



ENCYCLOPEDIA OP PRACTICAL HORTICULTURE 



any indication of the so-called "fire 

 blight." This is true in serious crown 

 and root infection. 



The term "collar-rot phase" is a not- 

 ably bad one, simply because the germ 

 does not produce a rot. The germ caus- 

 ing pear blight does not belong to the rot- 

 producing group of plant parasites. Even 

 the term "pear blight" is not a good one; 

 it would be best to make use of the term 

 "pome blight," or better, ''bacterial pome 

 blight." There are certain other diseases 

 of pome fruits which often produce effects 

 somewhat resembling the bacterial blight, 

 and therefore it would be much better in 

 speaking of blight to qualify it. If we 

 would use the term "bacterial blight" in 

 the case of pears, apples, quinces and 

 other pome fruits we would not fall into 

 error. 



As stated above, in order to have a 

 general infection, or for that matter any 

 infection, the blight germ must be pres- 

 ent. It has been demonstrated that this 

 germ will live during the dormant sea- 

 son of the tiee in the cankers formed 

 by the previous year's infection ot limbs, 

 bodies or roots of pome trees. No part of 

 a pome fruit tree may be free from in- 

 fection. The germ is carried fi^om these 

 centers called "hold-overs" by various 

 agencies, principally insects. However, 

 birds and other animals, even man him- 

 self, may be distributing agents. 



For a good many years, besides having 

 charge of eradication work, the writer has 

 done much investigation work in deter- 

 mining the relation of various carriers of 

 infection to blight epidemics. A very 

 large number of species of insects and 

 their near relatives have been studied. 

 Not only flying insects have been found 

 to be effective in spreading infection, but 

 also many insects and insect-like species 

 which do not depend upon flight have 

 been found particularly dangerous. In 

 this short article we cannot discuss the 

 various insect agencies; however, it is 

 enough to say that insects and their near 

 relatives are the most important factors 

 in the distribution of the germ of blight. 



Upon the control of blight, therefore, 

 depends in a great measure the control 

 of insects. However, in the first place 

 all sources of infection, namely, the hold- 

 over cankers, should be carefully eradi- 

 cated. This is a difficult thing to do, for 

 the reason that the most careful worker 

 will often miss hold-over blight. We know 

 that there are varieties of pome fruits 

 which are very sus.ceptible to the disease; 

 others that are quite resistant. We often 

 hear of varieties being "immune," but, so 

 far, no species of the pome family has 

 been found immune to blight. There are 

 various degrees of resistance, and that 

 is about all that can be said. Very often 

 the attention of the fruit grower is di- 

 rected away from resistant varieties by 

 the statement that they are so resistant 

 that blight will not hold over in them. 



However, every fruit grower knows 

 that our cultivated varieties are not grow- 

 ing on their own roots. For instance, a 

 Bartlett pear is not all Bartlett; a New- 

 town apple is not all Newtown, and so on. 

 Until recently no attention was paid by 

 the nurservmen to blight-resistant stock 

 upon which to work our commercial va- 

 rieties. In the main, our commercial va- 

 rieties of pears are all worked on French 

 stock which is very susceptible to blight. 

 Our apples are also worked on seedling 

 stock which is never selected for resist- 

 ance. Prom this it can be readily seen 

 that, although the variety top-worked on 

 the stock may be quite resistant, the 

 stock or root being very susceptible 

 renders the tree unsafe. 



It is often said that a chain is no 

 stronger than its weakest link, and, in 

 the same way, a variety is no more re- 

 sistant than its least resistant part. If 

 the root system is very susceptible, the 

 tree may be lost although apparently 

 there may have been no infection noted 

 above the ground. I have seen the worst 

 cases of blossom and twig infection in 

 very resistant varieties where not a single 

 hold-over could be found in the orchard 

 itself, or in the immediate vicinity, so 

 far asi the examination of the parts above 

 the ground was concerned. However, by 

 roting the infection centers, examination 



