166 ARMILLARIA MELLEA, 
stumps within the area must be examined for signs of rot. 
Infected stumps break apart fairly easily and show plates 
of deep black tissue. Further procedure will depend on the 
extent of the area to be treated. If this is not too large the 
infected stumps should be grubbed up, a process which is 
far easier when the stumps are rotted than when they are 
fresh, and all parts burned. If this involves too much 
labour, isolation trenches should be dug round the stumps, 
and cut to a depth at which no more rhizomorphs are 
encountered. 
By this means the chance of infection of neighbouring 
trees will be greatly reduced, as the rhizomorphs outside 
the trench, being cut off from their chief base of supplies, 
will be greatly weakened. But it may be found that some 
living trees, which in the summer showed no sign of attack, 
already have Armillaria growing from their roots, as in 
figs. 69 and 70. From the base of these trees the soil should 
be removed, and if it is found that only a few roots are 
infected, these roots must be cut through above the points 
of attack and grubbed up. If, however, the fungus has 
grown into the trunk, as shown by plates of white mycelium, 
it is better to grub up the whole trees, utilize the upper 
part for what it is worth, and burn the remainder, otherwise 
the trees will die shortly and become fresh bases for fungal 
invasion. Those who pin their faith to isolation trenches 
should remember that these are of no value unless they are 
kept open for a long time, for the fungus is long-lived and 
may grow on a single oak or beech stump ten years or 
more. If, on the other hand, an infected stump is removed, 
a trench is unnecessary, as the rhizomorphs still in the 
ground are incapable of growth when they have been 
severed from their base, unless they have already penetrated 
the roots of other trees. 
The success of the measures adopted can only be tested 
in the following autumn. If the toadstools come up again 
next year, it is a sure sign that undiscovered bases had been 
left, and further treatment along the same line is necessary. 
It may take several years to eradicate a well-established 
