FIRE – BLIGHT.

New Zealand Journal of Agriculture, Volume XX, Issue 3, 20 March 1920, Page 156

FIRE - BLIGHT.

A SERIOUS DISEASE OF FRUIT-TREES.

A. H. COCKAYNE,

Biologist

In December last alarming reports were published in various newspapers in the Dominion concerning a new fruit-tree disease that had appeared in the Auckland Province. Officers of the Horticulture Division and Biology Section have made a complete investigation into this outbreak, and the disease has been fully proved to be the dreaded American fire-blight, a bacteria] disease caused by an organism known as Bacillus amylovorus Burr. ’ In North America fire-blight has caused probably more loss than any other single fruit-tree disease. Unless adequately controlled in the Dominion it is liable to prove disastrous to our fruitgrowing interests, especially as it is particularly prone to attack apples and pears. To a limited extent it is also known to infect certain stone-fruits, more particularly apricots and cherries, but it is on pip-fruit that its ravages are rightly dreaded, and it is just on this class of fruit that the future of our orchard development depends.

Fortunately, at the present time fire-blight appears to be confined to the Waikato, with outlying areas of infection in the Tauranga district and the outskirts of Auckland south of that city. It is essential that every effort should be made to eradicate the disease, so as to avoid its distribution into the main fruitgrowing sections of the Dominion. Once well established in the main pip-fruit districts it might (well be only the matter of a year or two before the whole of our fruitgrowing industry would be seriously menaced.

The control of fire-blight is difficult insomuch as spraying is of no avail, and the only method to adopt , lies along the line of complete removal of all diseased portions of the affected tree. The main period of infection is in the late spring and early summer, when flower and shoot infection occurs. This is followed by a period of comparative quiescence of the organism,-which winters over in cankered areas on the branches of the trees, followed again by rapid growth and fresh infection in the following year. Flower-infection is extremely serious, as it causes complete destruction of the crop.

Both flower 'and shoot infection can be prevented by systematic removal of all infected wood prior to the blossoming-period. All infected shoots, and laterals, &c., carrying infected flower-buds, should be cut away at least I ft. below the apparent infection. Where the grower is desirous of saving any large limbs bearing cankers he should remove the cankered areas with a sharp knife, cutting well outside the affected area. All knives, seccateurs, &c., used should be sterilized at each cut, which will prevent the further spread of the disease by such tools. The wounds left after cutting out should be sterilized with a 5-per-cent. solution of formalin, lysol, or similar disinfectant, and then coated with a dressing of coal-tar.-

. An extremely important point to remember is that the disease can winter over in branches that have been cut from the tree, so that the immediate burning of all prunings and cut-out' cankers is essential. The systematic removal of all affected wood is a slow and tedious process, but the orchardist has the whole of the late autumn and winter (the quiescent period of the organism) in which to carry out the work.

A full account of the life-history and control of fire-blight is under preparation, and will be published in the Journal in the near future.

—The subject of fire-blight is also dealt with in " The Orchard” monthly notes later in this issue.Editor. ■ .