24 



WINTER INJURY IN ORCHARDS. 



By F. M. Clement, Macdonald College. 



Winter injury to fruit trees appears in many different forms and on 

 all parts of the tree including the roots, but to-day we are particularly 

 interested in that form which during the last few weeks has made itself 

 manifest on the trunks of certain varieties of apple trees in one of the ex- 

 perimental blocks. In late January and early February the trunks of 

 some of the trees in certain rows in block six were noticed to be split- 

 ting on the south and south-west side. At first it was not thought to be 

 serious but later when the injuries or splits becam.e more prominent, 

 some as much as eighteen inches in length and one-half inch in breadth, 

 it -v^^as decided to study the question a little more closely and detect, ii 

 possible, the cause or causes. Such wounds in themselves are quite set- 

 ious, especially ^vhen desiccated from- long exposure to wind and sun, but 

 they are made doubly serious if not treated to prevent the admission of 

 the spores of Saprophytic Fungi and especially Black Rot spores with 

 the consequent development of apple canker. As yet no serious disease 

 has gained a foothold in the orchard, and it is hoped that \vith careful 

 treatment the damage will not prove to be as great as the injuries at 

 present indicate. 



All normal growing trees contract on freezing in degrees varying 

 with the changing temperature. In the Geneva experiments it was found 

 that eight apple trees of different varieties contracted from 1.7 per cent 

 to 3.1 per cent — an average of a little more than 2 per cent between the 

 greatest extremes. It has generally been supposed that the w^ood and 

 bark of growing trees, like vt^ater, expands on freezing, and that the split- 

 ting is caused by the increased bark tension due to this expansion;^ but 

 as I understand the question from observation and reading the results of 

 the Geneva experiments, the co-efficient of contraction or expansion of 

 bark on freezing is greater than the co-efficient of expansion or contrac- 

 tion of wood on freezing; also bark being exposed freezes more quickly; 

 consequently an opening or split must occur if the tension is to be reliev- 

 ed. Or it may be explained thus: th co-efficiency of expansion or con- 

 traction of the circumference is greater than the co-efficiency of expan- 

 sion or contraction of the radius, consequentlv splitting must occur when 

 the expansive force becomes greater than the cohesive powers of the 

 \vood particles ( Geneva Bulletin 23, including report from German invest- 

 igations ) . In such cases cracks sometimes appear in the wood also. 



It is also interesting to note that these tests indicate that contrac- 

 tion is greatest at lo\vest temperatures or increases with the fall in tem- 

 perature. From 6.60C to 9.4OC the average rate of contraction was .19 

 mm per degree of change of falling temperature ^vhile from 9.4 OC to 

 28.3 OC it was 46 mm per degree or about 2 1-2 times as great. This is 

 also in accord with our own observation, v^'^hich show the injuries or 

 splits to be ^vider and more pronounced on the coldest days, closing, some 

 wholly, some partly, amd a few where the bark is badly loosened not at 

 all on the warm days. 



