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 foliage, 
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 established. Insects thrive on 
neglect; the rubbish around the base of the tree, the prun- 
ings and fallen leaves 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 pupz 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 
