448 ANNUAL REPORT OF THE Off. Doc. 



others. The seedliug stocks are, of course, an absolutely unknowu 

 thing, as to their susceptibility to blight. With our horticultural va- 

 rieties, which constitute only the upper half of the tree, we have 

 learned by years of experience how they behave when attacked by 

 blight. 



It should be noted that trees injured or dying with blight at 

 the collars and on the roots behave not unlike those affected by 

 other troubles. In fact such trees die in very much the same man- 

 ner as a tree dying from root rot. This fungous root rot is rather 

 abundant in apple orchards of Pennsylvania as well as other Eastern 

 States. At least two types of frost injury also very closely resemble 

 pear blight at the collar. In one of these the tree is injured from 

 the soil line upward, usually on the sunny side but not always so. 

 Blight is easily distinguished from this winter sun scald when the 

 latter occurs as an elliptical area on the main trunk of the trees 

 from the soil or snow line nearly to the branches. On the other 

 hand another type of frost collar girdle reaches but a little above the 

 soil line or only occasionally extends upward in a v-shapod area but 

 spreads well under the ground, partially or wholly girdling the tree. 

 Still another type is that of root winter killing. In this case the 

 roots near the surface of the ground ar^ frozen and killed, while 

 the top of the tree may or may not Ije injured by frost. It is neces- 

 sary to know these other collar injuries in order to distinguish them 

 from true collar blight. 



Treatment. — Referring again to the factors influencing pear 

 blight, it will be noted that the presence of the germ is of primary 

 importance. If the pear blight germ is not present in the orchard 

 or in the immediate vicinity there can be no blight. When spring 

 opens up and new growth begins, if the germs are present or con- 

 veniently nearby, and the conditions favorable, blight has a great 

 opportunity to spread and accomplish its work of destruction. If. 

 on the other hand, the germs do not occur, no matter how favorable 

 conditions may be, there can be no blight. The main method of 

 controlling pear blight is to cut out the holdover blight. This is 

 usually best done in the autumn but it may be done at any time 

 through the winter or early spring before the blossoms appear. 

 When blight occurs on the main limbs or on the collars of the trees, 

 one of the principal things in combating the disease is to find all 

 the cases, especially where the blight occurs under the rough bark. 

 It requires close examination to find and remove all the i^light in the 

 tops of the trees, but this can best be done in the summer or earlv 

 in the autumn while the foliage is still on, the blackened dead leaves 

 enabling one to easily locate the blighted branches. Summer cutting; 

 out of pear blight must be regarded, however, as of secondary im- 

 portance in the treatment, though still a good thing to do. On rap- 

 idly growing twigs and branches it is usually necessary to cut a foot 

 or more below the lowest discoloration of the bark. In winter 

 pear blight cutting, it is usually possible to cut pretty close to the 

 blight, say four to six inches, or, where it has thoroughly died out 

 an inch may do. On the other hand when the blight blends off 

 imperceptibly from the dead bark into the live bark, as it often does 

 in summer, from one or two feet below the lowest point may be con 

 sidered necessary. 



