Fireblight Erwinia amylovora

Damage. This disease, which first appeared in the British Isles in 1957, can cause serious damage on members of the Rosaceae family. Individual branches wilt and the leaves rapidly turn a 'burnt' chestnut brown. When the disease reaches the main trunk, it spreads to other branches and may cause death of the tree within six weeks of first infection, the general appearance resembles a burnt tree, hence the name of the disease. Badly infected plants produce a bacterial slime on the outside of the branches in humid weather. On slicing through an infected stem, a brown stain will

Erwinia Amylovora Life Cycle
Figure 15.17 Fusarium wilt on beans. Note the leaf yellowing

often be seen. Pears, hawthorn and Cotoneaster are commonly attacked, while apples and Pyracantha suffer less commonly.

Life cycle and spread. The bacterium is spread by bees as they pollinate, by harmful insects such as aphids and by small droplets of rain. Humid conditions and temperatures in excess of 18°C, which occur from June to September, favour the spread. Natural plant openings such as stomata and lenticels are common sites for infection. Flowers are the main entry point of entry in pears. The bacterial slime mentioned above is an important source of further infections. Fireblight, once notifiable nationally (see p293), must now be reported only in fruit-growing areas.

Control. The compulsory removal of the susceptible 'Laxton's Superb' pear cultivar in the 1960s eliminated a serious source of infection. Preventative measures such as removal of badly infected plants to prevent further infection, and removal of hawthorn hedges close to pear orchards, help in control. Careful pruning, 60 cm below the stained wood of early infection, may save a tree from the disease. Wounds should be sealed with protective paint, and pruning implements should be sterilized with 3 per cent lysol.

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