The remarks which follow apply for the most part to that phase of Frost Injury commonly known as winter injury. Properly winter injury includes injury to all parts of the tree caused by low temperatures in the winter months. Some attention will be given to injuries due to spring frosts, but the general statements are made with a view to an explanation of the important problem of winter injury. Of all the phases of Frost Injury, sun-scald and crown Rot, or collar Rot, are most prominent and will therefore receive proportionate attention. Sun-scald is now regarded as a late form of winter injury, while crown Rot is an early form of winter injury. The term Frost Injury is used broadly to include all injuries to fruit - trees due to the action of low temperatures without regard to the season of the year.
For many years it has been commonly observed that most fruit - trees suffer from the effects of severe cold and of sudden and extreme temperature changes in the cooler seasons. Authenticated records date back for a century and unquestionably the trouble was as common then as it is now. Theories were advanced immediately in earlier times to explain the occurrence and action of frost, some of which are still prominent, although each has been modified in some degree. All kinds of fruits are injured at some time or other; however, there is noticeable difference among fruits in this respect. It is generally accepted, for example, that while the apple is severely injured by cold, the peach is the more susceptible.
In the northeastern United States such apple-varieties as the Ben Davis, Northern Spy, Baldwin, Rhode Island and Tompkins King are all likely to suffer from cold. Others, such as the Oldenburg, Grimes and Hubbardston, often exhibit signs of injury from low temperatures. But these varieties are not invariably injured; and on the other hand those varieties omitted from the list are not always free from the trouble. Frost Injury seems to be confined largely to orchards between the ages of eight and thirty years. High-headed, severely pruned individuals of any variety on wind - exposed locations are most liable to the difficulty. Therefore, factors other than the nature of the variety condition the injury under consideration.
The role of Frost Injury in fruit crop-production is a prominent and important one. Growers of fruits in practically all temperate and even in semi-tropical regions know and fear this trouble. But not every one appreciates the actual damage done in each case. It is only after hard disastrous winters such as were experienced in the East in 1903-1904, 1904-1905 and 1906 - 1907 that general complaints and appeals for help are made. Trees are severely injured and often killed in the extremes of winter temperatures of the northerly sections. In warmer regions late frosts sometimes entail heavy losses.
Frost Injury involves all parts of the tree. Injury to aerial parts only are evident to the casual observer. A reliable symptom of fatal injury evident at the end of winter is not definitely known. Trees may appear entirely healthy, but on cutting into the bark above the snow line discoloration in the cambial region will be found. Trees, especially in low spots, affected by frost fail to start in the spring or they may make only a feeble growth. As the season advances they look unhealthy, the foliage is yellow, and finally death of the whole tree ensues (Fig. 8). Often a single branch or one side of a tree only is afflicted. Such trees on closer examination show frost - injured areas or cankers at one or more places (Fig. 9).
Injuries may occur chiefly on the southwest side of trees at a point midway between the crown and head, or they may be found at any place on any or all sides. Injuries may occur at any height on a tree; at the crown, the injury known as crown Rot or collar Rot; at the crotch, crotch injury; on the main limbs as they diverge from the crotch, known as sun-scald; at the roots, root injury. The tips of branches are sometimes killed back for some distance. Not infrequently the injury may extend from the collar to the head, involving large areas.
Crown Rot, or collar Rot, occurs at the crown or base of the trunk at the ground line. It is distinguished from sun-scald and crotch injury by its position on the tree. It is normally an early form of win-ter injury. Observations indicate that it may occur from October to December in the latitude of New York, Ohio and Connecticut. The Tompkins King, Grimes and Hubbardston are most subject to crown rot. In such injured places the bark appears discolored, dead and loosened from the trunk, sometimes split open, exposing the wood. Again the injured bark clings to the wood for a time, forming a canker at the crown.
Sun-scald is usually made evident in the late spring by the death of the bark on the southwest or sun-exposed side of a tree. The frosted bark may peel, exposing the discolored sap-wood; or sometimes it adheres closely to the wood and a sunken, cankered area is thus formed. In some cases the sapwood is killed and the cambium is left alive to form new wood outside the dead area. The sapwood is stained by the diffusion into it of some substance apparently originating in the protoplasm of the affected tissues. When the wood is thus discolored it is called black-heart. This type of injury is common in the northern United States. Frost-killed areas in the bark are commonly inhabited by saprophytic and weakly parasitic organisms, prominent among which is the New York apple - tree canker fungus, Physalospora Cydonice.
Fig. 8. - Apple - tree nearly dead as a result of low temperature injury.
The name sun-scald owes its origin to the common belief that it is due to some interaction of sun and cold on the sunny side of the tree in late winter. It involves the crotches and the adjoining sun-exposed bark of the trunk and limbs as well. The Ben Davis, Stark and Twenty Ounce varieties are generally regarded as most susceptible to sun - scald. Trees leaning to the northeast are most severely injured.