4 
FRUIT TREE CANKERS AND THEIR CONTROL. 
branches or trunks. This is quite often followed by the gum for- 
mation commonly seen on both plums and cherries. The common 
fire blight which has been serious in Minnesota in recent years 
may cause serious cankers on branches and trunks of apple trees. 
The black rot fungus, responsible for the black rot of apples, also 
causes cankers on the woody parts of the tree. Black rot cankers 
are especially serious following fire blight. 
CONTROL OF CANKERS 
After a canker is once formed, control measures, regardless 
of the primary cause, are quite similar. However, getting rid of 
cankers after they have once formed is much more difficult than 
preventing them. 
If an orchard is kept perfectly healthy and all wounds are 
immediately protected, there is not much danger that cankers 
will get staited. The first essential, therefore, in preventing 
cankers is to control all diseases. On plums, brown rot should 
be thoroly controlled. Details for the control of this disease 
are given in Minnesota Bulletin 153, also in the Minnesota Horti- 
culturist (Vol. 43, pp. 231-233; and Vol. 44, pp. 144-151). Black 
rot of apples can be controlled very largely by proper spraying. 
(See Minn. Bui. 153, pp. 26-27.) Fire blight can be controlled 
only by keeping the orchard clean and cutting out the blight from 
all trees. To guard against the spread of fire blight by 
PRUNING, THE TOOLS USED IN THE OPERATION MUST BE WASHED 
OR DIPPED IN A 1 TO 1,000 SOLUTION OF CORROSIVE SUBLIMATE 
BETWEEN EACH CUT.* Dormant washes may help somewhat, but 
it is doubtful whether the application of the dormant wash pays 
in Minnesota. 
Much trouble can be avoided by proper pruning. (See Fig- 
ure IV.) Whenever trees are pruned, the wounds should be clean 
and near the surface of the trees. Stubs should never be left. 
Wood rot and canker fungi very often enter them. Cut off suck- 
ers in order to prevent the rapid development of fire blight. All 
dead material should be promptly removed and burned. The 
trees should be properly pruned in order to provide good aeration 
so that the canker fungi will not get started so easily. 
•Directions for making this solution can be obtained from any druggist when the material 
is purchased. Corrosive sublimate is a deadly poison if taken internally, 
