Orchard Pests and their Control 377 



is their mode of living over winter. In the great majority of 

 instances the organisms die as the tree takes on its dormant con- 

 dition. In the eastern states there is but little evidence of the 

 disease being in an active state of growth after the middle of the 

 growing season, for the reason that the tissues become hardened. 

 These germs thrive best in rapidly growing, succulent tissue. 

 But under irrigation trees are often kept growing late in the 

 season, much to their detriment, so that blight is sometimes found 

 in an active state in October. A definite boundary between live 

 and dead bark is an indication that the germs are dead, and this 

 is the usual appearance of blighted limbs at the close of the 

 season. But a few blighted areas may always be found where 

 this separation is not distinct, and it is in these that the germs 

 live over winter. The following spring the organisms start into 

 growth with the activity of the tree, and a thick juice is exuded, 

 which runs down the branch or trunk. This juice contains count- 

 less numbers of the germs of pear- blight, and it is from such cases 

 of " hold-over blight " that many new infections ultimately arise. 

 If there were no cases of hold-over blight, there would be no 

 source of infection, and the disease would be a thing of the 

 past. 



It should be easy to understand, with these facts in mind, 

 that no spray or wash that might be applied to a tree would 

 have the slightest effect in controlling blight. But now that the 

 life history of the disease is known some preventive measures may 

 be taken which will lessen the amount of damage. 



The removal of all hold-over blight in the fall should be men- 

 tioned as of first importance. The trees should be gone over 

 carefully in the fall and again in spring, and all blighted limbs cut 

 out. It does not seem to be possible in actual practice to detect 

 them all, but much good may be accomplished in this way. Dis- 

 eased branches should also be cut out during the summer to pre- 

 vent further injury to the tree as well as to reduce sources of 

 infection. Care should be taken, particularly in the summer, to 

 make the cut ten or twelve inches below any sign of discolored 

 bark or wood, so that no germs may be left. And as a further 

 precaution the knife or saw should be disinfected after each limb 



