Pests and diseases of trees
Those affecting ornamental trees can be divided into three main classes: disease due to bacterial or fungal action, damage caused by insects and damage caused by animals (including birds). Of the first, the most seriously affected trees are members of the rose family (Bosaceae).
Bacterial canker attacks cherries and plums. It is associated with the oozing and dripping of gum from branches or the trunks. Some control can be obtained by pruning out branches affected.
Silver-leaf also affects plums, cherries and apples in particular and occasionally thorns and laurels. The leaves take on a silvery appearance and on a branch that dies a purplish-mauve fungus arises. This should be cut out and burned without delay.
Fire blight may attack pears, hawthorns, rowans, whitebeams, and pyracanthus. Whole shoots in leaf go brown as if burned and die. If this is found, the Ministry of Agriculture, Fisheries, and Food must be notified at once. The most serious `killer’ fungus is the honey fungus. It occurs generally on the ground that has been woodland which has been cleared with the stumps or many large roots left in the ground. Root-like growths, resembling boot-laces spread through the soil and infect a healthy tree, which is eventually killed and should be removed. From the ground around it, toadstools may, but do not always, arise. They are pale yellow, the gills on the underside running a little way down the stalk, which carries a collar-like ring around it. There is no known cure. It attacks conifers.