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The Canadian Horticulturi^ 



Vol. XXXIV 



JANUARY, 



No. 



"Fire Blight" Successfully Combated* 



IN order to successfully cope with a 

 disease, whether it be a disease of ani- 

 mals or of plants, it is most desirable 

 to know its specific cause and its methods 

 of attack. Practically all that is known 

 concerning the precise nature of infecti- 

 ous diseases, both of animals and plants, 

 has been learned during the last thirty 

 years or so. Everyone now is familiar 

 with the precautions necessary to prevent 

 the spread of typhoid fever, cholera, tub- 

 erculosis and anthrax, and other infec- 

 tious diseases in man and animals. Indi- 

 viduals suffering from these diseases are 

 isolated as far as possible and care is 

 taken that all discharges from their bodies 

 are burned or otherwise disinfected. These 

 precautions are necessary because these 

 diseases are the result of micro-organisms 

 gaining access to the body through water, 

 food or wounds, and there rapidly mul- 

 tiplying. Their multiplication produces 

 the symptoms of the disease, and as mil- 

 lions of the germs are soon produced in 

 the body from a few that have gained en- 

 trance, some of these are given off in the 

 di.scharges, and if these are not destroyed 

 they are liable to spread the disease to 

 whoever comes in contact with them. 



The disease of some trees known by 

 the various names of fire blight, pear 

 blight, apple twig blight, body blight, 

 and blight canker, is a bacterial disease, 

 and hence if its spread is to be prevented 

 precautions must be taken somewhat sim- 



•An address delivered at the annual convention 

 of the Ontario Fruit Growers' Association hold in 

 Toronto last November. 



D. H. Jones, O. A. C, Guelph, Ont. 



ilar to those found necessary in dealing 

 with bacterial or infectious diseases of 

 man and animals. 



So far as is known, the disease is pe- 

 culiar to North America, where it has 

 caused immense losses to pear and apple 

 growers. In addition to being found on 

 the cultivated and wild varieties of apple. 



C0i / J> 



Apple tree badly attacked by "Fire blight" 

 through blossom inoculation in spring and twig 

 inoculation by aphids. Eighty per cent, of twigs 

 and amall brancheg killed out in one season. 



..V''. 



B.acilus amylovoi ,..,. ,i.r s>.iiu wliich causes the 

 blight. Magnified 1000 times. 



pear and quince trees, it is common on the 

 juneberry, hawthorn and mountain ash, 

 and occasionally it is found on the plum. 



EFFECTS OF THE DISEASE 



The disease is caused by a microbe 

 known as "Bacillus amylovorus," which 

 on gaining entrance to the bark of a tree 

 subject to its attack, rapidly multiplies 

 there and in doing so kills the bark. If 

 the bark attacked be that of a twig, the 

 twig with its leaves, blossoms or fruit 

 will wither, turn brown and die. If the 

 bark attacked be that of the trunk or 

 main limb, the result is a canker of the 

 area attacked. The cankered area is us- 

 ually darker colored than the healthy part, 

 is somewhat sunken, and usually sur- 

 rounded by a crack. If the cankered 

 bark be cut, it will be found to be brown 

 and tough instead of being white or light 

 green and tender. The canker in the ap- 

 ple tree does not usually spread to very 

 great dimensions except in a few varie- 

 ties, principally the Russian varieties. 

 With the pear tree, however, it is dif- 

 ferent, for when the bacillus finds en- 

 trance to the bark of the trunk or a main 

 limb of a pear tree it usually continues to 

 spread there until it has killed the tree. 



PEAR TREES SUSCEPTIBLE 



For the disease to spread rapidly in a 



tree it is necessary that the affected bark 

 be juicy. The bark of the large limbs 

 and trunk of the pear tree is softer and 

 more juicy than that of most varieties 

 of apple trees. Hence it is that the dis- 

 ease spreads more rapidly and does much 

 more damage in the trunks and large 

 limbs of the pear than in those of the 

 apple. On the other hand, the bark of 

 the twigs and young shoots of the apple 

 is softer and more juicy than that of the 

 pear twigs, and consequently blight of 

 the apple trees is usually in the form of a 

 twig blight, all the )'Oung growth on a 

 tree often being killed in one season. 



Trees in sod are not so sappy as those 

 under cultivation. Hence it is that the 

 disease kills off trees in well cultivated 

 orchards more often and more rapidly 

 than in orchards that are in sod. How- 

 ever, sod is not the ideal condition for an 

 orchard. It not only curtails the produc- 

 tion of fruit and hinders the development 

 of the tree in general, but it harbors 

 numerous insect pests for which it is a 

 good breeding ground. We must, then, 

 if we are to get the best results from 

 our orchards, cultivate them and find 

 some other means of keeping the blight 

 in check than by leaving them in sod. 



HOW THE BLIGHT IS SPREAD 



Insects, more than any other thing, 

 are responsible for spreading the blight. 

 It was demonstrated a few years ago that 

 bees, wasps and other blossom visiting 

 insects often carry the germs of the 

 disease on their bodies, especially their 

 mouth parts, to the blossoms they visit 

 in the orchard. When they insert their 



Young pear tree, with one branch inoculated 

 with the germs by the pruning saw. The branch 

 was killed and the disease was spreading from 

 this branch to the others. 



