The apple and the wild crab are commonly attacked by Fire Blight. In the nursery these forms are more seriously affected than pears. In the young orchard the disease is also injurious, but old bearing trees do not suffer materially. It is true that the latter class of trees frequently show a large amount of twig blight, yet the financial loss from such an affectation is negligible. While no variety is wholly immune, there is an apparent difference in susceptibility. Under nursery conditions there is evidence that the Yellow Transparent, Golden Russet, Sutton, Fameuse, Wagener, Tompkins King, Rhode Island and others are more affected than Ben Davis, Red Astrachan, Oldenburg and Gravenstein. In New York and neighboring states such varieties of the commercial orchard as Tompkins King, Baldwin, Grimes, Alexander and others are susceptible. In Virginia, the York Imperial and Grimes are most likely to show Fire Blight. In this and other regions one of the serious troubles in connection with apple-growing is a form of Fire Blight known as collar blight, collar Rot, or crown Rot. In many cases this type of trouble is a form of winter injury.

Symptoms

Large cankers may be developed on the collar of bearing trees, although these do not constitute the first noticeable signs of the disease. The leaves appear yellowish and smaller on one or more of the larger limbs, this effect developing gradually in contrast to the sudden darkening of the foliage of twigs infected with Fire Blight. Premature defoliation is induced. The canker is of variable size, depending on its age, and shows a dark, sunken, smooth surface. Cankers in which the pathogene is advancing do not exhibit a distinct margin as is the case with older infections. The lesion develops until midsummer when its growth is arrested, but is renewed the following season. Ultimately complete girdling and death of the tree may result. Usually the canker extends up the body of the tree into the branches; it may also extend down into the lateral roots. In case the collar Rot is due to weather conditions there is no progressive dying as is found in this type of Fire Blight. Furthermore winter injury is first seen at the beginning of the growing season, whereas collar blight is not observed until midsummer. Fire Blight cankers are known to develop commonly at the base of water - sprouts about wounds of various kinds on limbs and body.

Cause

This is a bacterial disease. It is caused by Bacillus amylo-vorus which also attacks the pear, quince, plum, apricot and other trees. The life - history of the parasite on apple may be understood by reading the account under Pear (page 327).

Control

For trees which are less than half girdled, surgical treatment is profitable. Otherwise, bridge-grafting can be followed as a matter of recourse. A draw-shave, mallet, chisel and farrier's knife are desirable tools for the surgery work. Remove the soil from the affected crown and roots. Cut out all discolored tissue, pointing the upper and lower ends of the wound. Wash the cut surface with corrosive sublimate, and after the wound is dry apply a wound-dressing, preferably coal - tar.

For a full discussion of this disease see Pear (page 323).

References

Whetzel, H. H. The blight canker of apple - trees. Cornell Univ. Agr.

Exp. Sta. Bul. 236: 103-138. 1906. Orton, C. R., and Adams, J. F. Collar blight and related forms of Fire Blight. Pennsylvania Agr. Exp. Sta. Bul. 136: 3 - 23. 1915. Hewitt, J. L. Twig blight and blossom blight of the apple. Arkansas.

Agr. Exp. Sta. Bul. 113: 493-505. 1913. Whetzel, H. H. Fire blight and apple - tree canker. Wisconsin Hort.

Soc. Ann. rept. 36: 215 - 226. 1906. Swingle, D. B. The pear and apple blight in Montana. Montana.

Agr. Exp. Sta. Circ. 2: 1-9. 1910. (Revised: pp. 1 - 14. 1911.)