While this disease occurs on a great variety of hosts, it is of most consequence on the apple. On this fruit it is almost invariably called Bitter Rot, in spite of the apparent unfitness of the name. The affected flesh is not always bitter. The names anthracnose and Ripe Rot have also been applied to this disease, but since the trouble occurs on both green and ripe fruits, the latter term is an objectionable one. The name anthracnose is reserved for another disease of the Pacific Northwest. The disease on the limbs is called Bitter Rot canker.
It is difficult to determine the origin of Bitter Rot, but America appears to be the only country in which apples suffer from it. It was recorded in North Carolina in 1867, and with the development of apple-culture throughout the central belt of states, the range and destructiveness of this disease have gradually increased. By 1887 Bitter Rot had become a serious trouble in many eastern states along the thirty-seventh parallel. It now occurs in all the territory east of the Mississippi River, and west including Kansas, Oklahoma, Texas, Missouri, Arkansas and Louisiana. Within this region Bitter Rot is most prevalent in a belt of states on the line of the Ohio River, from Virginia to Oklahoma. Epiphytotics in many of the states in this belt have occurred with great frequency and destructiveness.
Bitter Rot is unquestionably the most ruinous of all apple diseases in certain years; this is particularly true of the section where it is most prevalent. This disease, more than any other apple disease, is one to be feared by apple-growers. Its sudden appearance after great expenditures of time, money and energy have been made in producing a fine crop causes it to be especially dreaded. A large harvest may be totally lost in a few days. Bitter Rot has probably done more to discourage apple - growing in many regions than all other fungous and insect pests combined.
The losses resulting from this disease are of two sorts; namely, injury to the fruit, and injury to the limbs. Affected fruits are rendered worthless, so far as their market value is concerned, the decay-process being rapid and complete. The amount of the losses incurred in some years has been so great as to cause many apple-orchardists to abandon the business. Instances are on record where bearing apple-orchards have been leased at $5 an acre for a period of five years, the grower choosing to be guaranteed this small sum rather than venture getting nothing from his trees on account of the bitter-rrot disease. It is estimated that in four counties in Illinois the loss due to this disease was $1,500,000 in one season. Single growers sometimes lose 10,000 to 20,000 barrels of apples, while the damage to the apple-crop of the United States in 1900 was estimated at $10,000,000. Bitter Rot cankers are destructive, like other cankers, in that the bark is killed. In many cases limbs are girdled and death of the affected member results.
Not all apple - varieties are affected alike. In Virginia the Yellow Newtown (Albemarle Pippin) is preeminently the greatest sufferer. On the other hand, the Winesap is conspicuous because of its resistance. The Ben Davis is said to be one of the most susceptible varieties in the Middle West; in Virginia, however, it shows a comparatively slight tendency to rot. Along the Atlantic seaboard the York Imperial and the Grimes are regarded as relatively resistant. The Willow and Huntsman are listed as susceptible in Missouri and Illinois.
Bitter Rot may be expected to show on the fruit at any time from June to October, although July and August are Bitter Rot months. The time of the first appearance varies with the geographical location, with the age and variety of the fruits concerned, and with the weather. It is the rule that a fruit shows but one or only a few spots (Fig. 5); but in cases of severe infection as many as 1200 separate lesions have been counted. Where only a small number of spots occur these continue to enlarge, merging with each other until the whole fruit is involved. If a great number of lesions begin simultane-ouslv on the same fruit, only a few continue to spread, the greater number remaining as small, brown, raised blisters on the surface. A lesion begins as a small light-brown discoloration beneath the skin. It rapidly enlarges and remains firm in texture and circular in form (Fig. 5). The color very soon becomes dark-brown and when about one-eighth of an inch in diameter the rotted area is distinctly sunken and sharply defined. When about one-half of an inch in diameter small black dots appear at more or less irregular intervals beneath the epidermis of the sunken area. These may be arranged concentrically or scattered without order (Fig. 5). Eventually these little black dots, the fruiting pustules of the pathogene, break through the epidermis exposing pink masses at their tips (Fig. 5). As the spot increases in diameter the pustules follow rather closely the advancing circumference of the lesion. At the same time the spot is developing outwardly, it is also progressing inwardly, and a section made perpendicular to the surface, through the center of the spot, shows the rotted area to be funnel-shaped. Finally, the whole fruit is involved and a mummy is the result (Fig. 5). Some of the affected fruits fall while others cling to the tree for at least a year. Spots which have been re - tarded by cool weather have an especially prominent purplish margin. Many late infections are reddish or purplish specks, never developing further on account of adverse conditions.
Fig. 5. - Bitter Rot of apples.
Cankers are developed on the twigs, limbs (Fig. 6) and fruit-spurs. Trunks rarely show Bitter Rot cankers. Smaller twigs are sometimes wholly and suddenly killed, resulting in a twig blight. The Jonathan and Willow varieties are more subject to this type of injury than others. Most cankers on the limbs have at their center a dead twig or evidence of one having been there (Fig. 6). The canker is at first a small discolored area in the outer bark, the smooth edges of which are sharply set off, c oval in shape, measuring one or more inches in length. With increase in size the edges become more or less ragged and the surface is somewhat roughened. The dead bark is cracked and fissured. In some instances it is broken away, although it ordinarily dries out and adheres to the wood. The major portion of the canker is at last clearly depressed, while about the margin of the dead area is formed a callus.
Fig. 6. - Bitter Rot cankers.