Domestic Encyclopædia (1802)/Crab, in Fruit-trees

CRAB, in fruit-trees, a disease which attacks the bark, especially after transplanting them from the nursery: it destroys particularly the inner bark, by reducing it to a blackish powder, not unlike the smut in wheat.

Various conjectures have been formed, as to the origin of this formidable disorder, which is often very destructive, especially to apple and pear-trees; but none appears to us satisfactory. It is, however, very probable, that it arises from the inattention of gardeners, when transplanting young trees, so as to change their situation to a different point of the compass; for instance, by placing the northern side of the trunk towards the south; where the powerful rays of the sun parch, and in a manner burn, the tender bark. This supposition is confirmed by the circumstance, that the disease generally makes its first appearance on the south side of bark; though, we believe, it also frequently originates from external injuries done to the tree, such as blows, scratches, &c.

The most expeditious method of relieving a tree thus affected, is that of immediately cutting out the whole diseased part, with a very sharp gardener's knife, and not to leave the smallest trace of its discoloration on the trunk; for an imperfect excision is attended with inevitable ruin to the tree. As soon as the operation is performed, the wounded places must be carefully covered with a plaster, made of equal parts of fresh clay, garden-mould, and cow-dung; or with the medication mentioned in our first volume, p. 432, under the article Canker.