PEAR DISEASES 



164S 



is no more difficult to answer than the 

 question, "Why do we have enormous 

 yields of fruit or harvests of grain?" The 

 answer to the question as to why we have 

 more bountiful crops one year than an- 

 other is usually given by the average man 

 in a single sentence, "The conditions were 

 more favorable." In other words, the 

 reason why we have occasional phenom- 

 enal yields is because the conditions for 

 plant growth were unusually good. 



For our heavy crop of wheat we sowed 

 the seed at the right time and in the 

 proper amount, the soil had been pre- 

 viously well prepared, climatic conditions 

 during the entire season were favorable, 

 and, more than likely, we used good judg- 

 ment in taking advantage of nature. 



It must be remembered that the pear- 

 blight germ is a plant which depends upon 

 favorable conditions for its best develop- 

 ment; it must be "planted" on the right 

 soils and the conditions for its maximum 

 growth must be favorable, as in the case 

 of the wheat plant. While it is known 

 that disease-producing bacteria may be 

 more virulent at one time than another, 

 just as seeds may be more or less viable, 

 nevertheless the conditions for a disease- 

 producing organism's development must 

 be favorable or it will not develop so as 

 to cause what is called an "epidemic." 

 After all, an epidemic of pear blight may 

 be compared with an "epidemic of good 

 wheat crops." 



It must be remembered that a plant will 

 not make its best growth where conditions 

 are below normal. Change these condi- 

 tions for the better and maximum growth 

 or development of the plant is the result. 

 Those who have lived in the arid Middle 

 West have probably noted that if the dry 

 prairie is broken up and allowed to lie 

 without cultivation the following season 

 a magnificent crop of sunflowers will be 

 the result. Where did these sunflowers 

 come from? They certainly were not car- 

 ried there by birds or wind in the amount 

 necessary lo produce such a heavy crop. 

 The sunflower plants were there before 

 the land was plowed, but no one but a 

 botanist would have known them to be 

 sunflowers. Instead of being the rather 



tall, yellow-flowered plants which every- 

 one knows, they were merely minute, few- 

 leaved specimens, and instead of bearing 

 the large golden-yellow flowers, these 

 dwarfed sunflower plants produced but a 

 single flower, each having but one small 

 ray and but a single seed. However, 

 when the land was broken the conditions 

 for plant growth were improved and the 

 seeds from the dwarfed sunflower plants 

 instead of producing dwarfs produced vig- 

 orous plants. The "epidemic" of sunflow- 

 ers was produced simply by making condi- 

 tions favorable. The seed was planted 

 deeper and soil moisture was conserved. 

 This example of what the sunflower will 

 do under various conditions will illustrate 

 the point I wish to make, namely, that 

 the pear-blight germ, being a plant, 

 must be mfluenced by environment and 

 change of conditions. 



Cause of Serious Infection 



In order to have a serious pear-blight 

 epidemic the following conditions are 

 necessary: (1) The germ must be pres- 

 ent; (2) insect or other agencies for the 

 "sowing" or spread of the blight organ- 

 ism must be plentiful and active; (3) 

 conditions for the best development of the 

 germ after it has been "planted" must be 

 favorable. It is easily seen that there 

 can be no infection if the blight germ 

 is not present, and, turthermore, there can 

 be no epidemic even though the blight 

 germ be present providing the other fac- 

 tors are wanting. Those who have had 

 experience with pear blight know that it 

 will attack all species of the pome family, 

 and that any part of the tree may be- 

 come infected — blossom, twig, limb, body, 

 crown or root. 



Such expressions as "blossom blight" 

 "twig blight," "body blight," "collar-rot 

 phase," "root blight," "fire blight," etc., 

 are all in a measure misleading, as fruit 

 growers are often mistaken in thinking 

 that these terms indicate a different dis- 

 ease in each ease. The term "fire blight" 

 is not good for the reason that fire- 

 scorched trees do not resemble trees badly 

 blighted by the blight germ. Further- 

 more, serious infection which may result 

 in the death of the tree may not show 



