PEAR DISEASES 



1627 



equal. Exhaustive crops of fruit tend to 

 consume tlie food material of the tree and 

 help to check the blight to a certain ex- 

 tent. On the other hand, when the trees 

 fail to fruit from unfavorable conditions, 

 such as prolonged rains at the blossom- 

 ing period, there may not be the oppor- 

 tunity for infection, and the contradic- 

 tion to this principle may be observed. 

 From observation, orchardists know that 

 during rainy and cloudy weather insect 

 visitors, such as bees, are very rarely 

 found working in the blossom. Since the 

 bees are the principal distributors of the 

 blight germs, it can be readily seen that 

 if the entire blossoming period is covered 

 by rainy or cool weather there is little 

 chance for very serious and general in- 

 fection, although there may be consid- 

 erable holdover blight in the vicinity of 

 the blossoming orchards. 



The style of pruning the tree exerts 

 some influence not only on the behavior 

 of the blight, but also on the convenience 

 of the orchardist in eradicating the dis- 

 ease. The least desirable form of tree 

 Is the tall pyramid, having a central 

 leader with the fruit spurs on the main 

 trunk and water-sprouts at the base. In 

 this form of tree, any Infection of blos- 

 soms or sprouts readily goes into the 

 body, making it difl^cult to eradicate the 

 blight without practically destroying the 

 tree, or at least removing the principal 

 bearing area. The most desirable form Is 

 the broad vase-formed tree, clean and 

 free from water-sprouts at the base, hav- 

 ing no fruit spurs near the main trunk 

 and leaders, and having lateral twigs for 

 fruit-bearing at as great distance as pos- 

 sible from the crown of the tree. Such 

 a tree is also in a very desirable form 

 for other reasons, for it is easier to spray, 

 easier to prune after the top has been 

 formed, easier to gather the fruit, and 

 especially easier to examine and keep 

 free from blight. 



The weather at critical times, espe- 

 cially in the spring and summer, exerts 

 an important influence on the spread of 

 blight. In fact, the weather influences 

 dominate more equally the infection than 

 they do the spreading of the blight in the 



tr( es. We recognize certain spells or 

 weather conditions as infection periods, 

 and by following carefully the relation of 

 the blight to the weather the intelligent 

 fruit grower soon learns to anticipate 

 these difficulties. In fact, it was supposed 

 by many that the long, dry, hot summer 

 of the Western states, especially the 

 Pacific Coast states, gave such poor op- 

 portunity for pear blight that it was not 

 able to exist under the prevailing condi- 

 tions. Of course, we now know that this 

 is a fallacy, for, as soon as the germ was 

 introduced, it produced the disease abun- 

 dantly. Dry sunshine, while favorable to 

 the orchards, tends to produce a firm, 

 healthy growth of the tree and prevent 

 infection periods. However, constant 

 and intense sunlight produces another 

 result which may be noted here. Pome 

 fruits, as well as other fruits, under the 

 influence of dry, but sunshiny weather, 

 carry on their processes of growth and 

 assimilation in the very best possible 

 manner. The study of blight throughout 

 the West shows that where irrigation is 

 used on the one hand, and where there is 

 a natural supply of water on the other 

 hand, and where the orchards are kept in 

 a continual state of high nutrition by the 

 perpetual and uniform sunshine, the trees 

 are iieculiarly susceptible to the disease. 

 In the lower Sacramento valley in Cali- 

 fornia and in the Rogue River valley, 

 where irrigation is not resorted to, we 

 find that there is a great deal of soil 

 moisture, and in many favored spots the 

 water table is only a few feet below the 

 surface of the ground. Under proper cul- 

 tivation, where a dust mulch prevents 

 evaporation of the soil moisture, we find 

 that during even the driest seasons the 

 roots of the trees are amply supplied 

 with water. On the other hand, we also 

 find places where the water table is too 

 near the surface, and in this case the 

 trees are in a drowned condition; con- 

 sequently, perfect assimilation does not 

 go on, and for this reason such trees, 

 although situated in rich, nitrogenous 

 soils, do not blight badly. Where the 

 trees are growing at their best, the blight 

 germ feeds on the rich sugars in the 



