18(J STATE HORTICULTURAL SOCIETY 



rate one consisting of a tank on a raised platform, elevating the man who 

 holds the nozzle ten or twelve feet above the ground. Power spraj-ers 

 were discussed, but as they are made at present they are scarcely com- 

 mended to general use, although certain men have rigged up machines 

 that are very useful for their work. 



Pear blight is so well known in Michigan that it is scarcely necessary 

 to describe it in detail. The disease attacks the pear, apple, peach, quince, 

 crab apple, Siberian crab, and several other related plants belonging 

 to the pome family. The disease is known to be the work of a living 

 parasite, a microbe belonging to the bacteria. The cause of this disease 

 was discovered by Prof. Burrill of Illinois, in 1879, although the disease 

 has been known in this country one hundred years. The pear-blight mi- 

 crobe begins its attack in the spring on the blossoms. It grows in the cen- 

 ter of the flower and is able to penetrate the nectaries, and growls down 

 into the blossom and spreads into the fruit spurs and then down into the 

 tree. During the flowering period, if the trees are attacked by blight it 

 spreads with great rapidity from one blossom to another. This rapid 

 spread of the disease is due to the visits of insects. Bees and other insects 

 visiting the pear blossoms for nectar and pollen unwittingly carry the 

 blight germs from tiower to flower and from tree to tree. Occasionally 

 birds may carry the disease, and in this way it probably is communicated 

 long distances. After blooming time is over, the disease can still enter 

 the tree through the young green tips of the twigs. It also rarely enters 

 in tender, growing bark, but as a whole the blossom clusters in spring 

 and the tender tips after blooming is over and during summer are the 

 two main methods of infection. Even on the twigs the disease is probably 

 carried by insects and introduced by punctures. In artificial infection 

 it has been found impossible to introduce the disease on the twigs without 

 a puncture of some sort. 



The amount of damage done will depend upon a number of factors, such 

 as susceptibility of the variety, amount of moisture, age of the tree, and 

 amount of cultivation and fertilization. Certain varieties like Vicar, 

 Clapp's Favorite, and to a less extent Bartlett and Flemish Beauty, are 

 very susceptibile to the disease. Other varieties, like Angouleme and 

 Kieffer, are much less susceptible. However, it should be noted that this 

 is merely a difference in susceptibility, and in no case amounts to absolute 

 immunity. We have no varieties of pear, apple, and quince which are 

 immune to this disease. All will contract the disease and be blighted with 

 more or less severity. The disease is mainly restricted to the tender, suc- 

 culent, growing parts of the tree, and on its downward course in the 

 branches it is almost limited to the bark. The inner bark on the tree is 

 of course of this tender, succulent character during the period of growth. 

 The disease progresses very slowly, even on the vigorous young twigs, 

 rarely reaching more than two or three inches in a day, although possibly 

 it may spread twice as fast. Naturally the destruction of the bark and 

 cambium layer on the limb results finally in the killing of the limb, 

 although girdled branches may remain apparently alive a year or more. 

 Under favorable conditions, when the vessels are gorged with sap, the 

 microbes often overflow from the bark into the vessels of the wood. When 

 dry weather comes again the vessels, being clogged or destroyed, are 

 prevented from conducting water to the foliage, and the limb collapses 

 suddenly. Such occurrences have given rise to the popular error that 



