EXPERIMENT STATION BULLETINS. 299 



known as leaf curl, that produces a similar effect on the leaves. If on 

 examining some curled and knotted leaves, no plant lice are found, one 

 may be quite sure that the formation is not due to the aphids, but to the 

 plant disease. The habits of these lice are the same as those found on the 

 apple, cherry, and plum. They are wingless at first, but, later in the season, 

 both forms will be found. After they hatch from the egg in the spring 

 they produce living young, multiplying very fast, and do a great deal of 

 harm when numerous. 



Remedies. — Kerosene emulsion is the best remedy for the lice on they 

 leaves and tender twigs. The remedy should be applied if possible before , 

 the leaves curl, as it will be hard to reach them with any remedy when they 

 are protected by the leaf. 



The work of the lice on the roots is usually shown in the tree having a 

 sickly and unthrifty appearance, and it is said that one might mistake the 

 appearance for peach yellows. An unhealthy condition of a tree is not 

 necessarily due to the root louse. If the soil is partly dug away from the 

 roots and a few pounds of kainit sprinkled near the roots and the whole 

 covered, the application will benefit the tree. Kainit is a fertilizer and 

 will also kill the subterranean lice if there are any. 



DISEASES OF THE PEAK. 

 PEAR BLIGHT (Bacillus amylovvrus, Barrill). 



The disease of this fruit that is the most to be feared, is the one that is 

 commonly called "fire blight" or "frozen sap blight." It is really caused 

 by the development within the tissues of the germs of a minute bacterium, 

 which produces a sort of fermentation in the sap of the trees. They gain 

 entrance through the nectaries and the stigmas of the flowers, through the 

 soft tissues of the young leaves and stems, and through cracks in the bark. 

 The old name of "frozen sap blight" indicates that fruitgrowers have 

 keen powers of observation, as the freezing and thawing of the unripened 

 wood causes the bark to crack, and the germs are often thus admitted to 

 the tissues of the trunk and older branches. The name of "fire blight" 

 both describes the appearance of the disease and applies well to cases 

 where the bark is cracked by the drying influence of the sun in seasons of 

 drought. 



It has been noticed that trees which have grown slowly and have firm, 

 well-ripened shoots are less subject to blight than others that make a 

 watery growth and expose for a long time their soft shoots to the entrance 

 of the germs. Once inside, the germs multiply with great rapidity and 

 spread through the tree, but at a slower rate than is usually supposed. 

 The germs are conveyed from diseased trees to the healthy ones by insects, 

 which visit the flowers for the purpose of obtaining nectar, and the germs 

 then enter through the nectaries or stigmas and such other parts as may 

 favor their entrance. Although we have no direct evidence of the fact, 

 it is evident that they also are carried m the air and thus enter the leaves 

 and the cracks in the bark. 



Pear blight causes the leaves to turn a dark brown and may manifest 

 itself suddenly through the entire tree, although as a rule only a single 

 branch is affected at the start, depending upon the way in which the 

 germs have entered. 



