8161 IZ AON 
1(7 74 .) 
IVio. 
OFFICE OF 
STATE ENTOMOLOGIST 
UNIVERSITY FARM 
ST. PAUL, - MINN. 
Circular No. 51 
MAY 1. 1918 
FRUIT TREE CANKERS AND THEIR CONTROL 
BY 
E. C. STAKMAN AND A. G. NEWHALL, DEPARTMENT OF PLANT PATHOLOGY 
AND BOTANY, UNIVERSITY OF MINNESOTA. 
During the last few years cankers have been doing consider- 
able damage on fruit trees in Minnesota. They have been par- 
ticularly destructive on apple trees. Plum and cherry trees have 
also suffered somewhat. The average Minnesota orchardist does 
not pay much attention to cankers. The trees are quite often 
sprayed in the ordinary manner and, aside from the regular prun- 
ing, little more attention is given them. The trees must be care- 
fully watched and very well cared for if losses from cankers 
are to be avoided. It is therefore important to know the nature 
of cankers, the method of their action, and the means for their 
control. Every apple tree should be made to yield to its maxi- 
mum capacity; therefore, everything possible should be done to 
maintain the health and soundness of the orchard. 
WHAT IS CANKER? 
Canker is a popular term which is applied to certain types 
of injury on woody plants. It is usually applied to the death of 
the bark, followed quite often by a callus formation around the 
edge of the dead area. 
OCCURRENCE OF CANKERS 
Cankers may occur on any woody plant, but in this paper 
only those on fruit trees are discussed. They may occur on any 
woody part of the tree, being found frequently on twigs, limbs, 
and trunk, and quite often in the crotch of the tree. 
