128 Control of Parasites 



In a previous chapter we have seen how to deal with rot 

 fungi of the wood. Prevention is the only remedy. If 

 once established the fungi which produce root rot are as 

 difficult to combat, sometimes indeed impossible, as the rot 

 fungi in the wood. All that may be done, if a tree or a group 

 is infected, is to isolate it by digging a ditch around it, in 

 order to prevent the spread of the disease, making sure 

 that the ditch is deep enough and so located as to inclose 

 the infected area. The tree should then be removed and 

 the roots burned. Possibly an application of Bordeaux 

 mixture, more highly concentrated than for use on foHage, 

 may be advantageously applied. The rest of the ground 

 should then be put in healthful conditions as described in 

 the previous chapter. 



Insect Parasites. To prevent and check the injuries 

 of insects, as of fungi, much can be done by indirect 

 means. 



It is easier to ward off an attack of insects or to make 

 conditions unfavorable for their multiplication than to destroy 

 them after they are once estabHshed. Insects thrive on 

 neglect; the rubbish around the base of the tree, the prun- 

 ings and fallen lea\'es furnish welcome winter quarters to 

 many, and the uncultivated soil is more favorable to their 

 development than that which is frequently stirred and dis- 

 turbed. Attention to soil conditions and surface condi- 

 tions is, therefore, of value even in this direction. The 

 scraping of bark to reduce hiding places for the wintering 

 of pupae and eggs is also an indirect measure, but unfortu- 

 nately, as we have seen, may breed mischief in other direc- 

 tions, besides making the boles unsightly. 



By keeping the trees in vigorous condition, the results of 

 insect depredations can be minimized, perhaps in the case 

 of bark-beetles, entirely avoided; and by encouraging birds 



