2 BULLETIN 543, U. S. DEPARTMENT OF AGRICULTURE. 



DESCRIPTION OF THE DISEASE. 



Leaves, fruit, and twigs are affected, but the injury to the leaves 

 usually is the most serious phase of the disease. 



The first indication of injury to the foliage is the appearance of 

 small, nearly transparent, water-soaked areas. These are par- 

 ticularly noticeable when a leaf is held between the observer's eyes 

 and the sun. Later, the spots enlarge, turn darker, and at length 

 become dry and brittle. Then, as a final stage, they crack away 

 from the living tissues and often fall out entirely, giving the leaf 

 the so-called shot-hole appearance (PI. I, figs. 3 and 4). Sometimes 

 a number of spots, especially those near the margin of the leaf, will 

 coalesce, giving the leaf a burned or blighted appearance. Later, 

 these dead areas, composed of several spots which have run together, 

 may break away and fall to the ground, giving the leaf a peculiar, 

 ragged appearance. Infections may be so numerous as to injure 

 every leaf on the tree, they may be localized so as to affect seriously 

 only the foliage of certain limbs, or the infection may be mild all 

 over the tree, so mild at times as not to be especially important. 



Though the disease in its later stages on the leaves is difficult to 

 distinguish from spray injury, damage by shot-hole fungi, and some 

 other diseases, when it appears on the fruit, especially after it has 

 passed the first stage of its development, it is not easily so confused. 

 Minute spots, scarcely darker than the skin of the young fruit, denote 

 the first appearance of the disease. These spots soon become some- 

 what enlarged and gradually become darker in color. Later, as the 

 fruit enlarges, small cracks appear in the diseased areas (PI. I, figs. 8 

 and 9). Beginning with this stage, the disease is most characteristic 

 and is not easily confused with any other type of injury. Later, with 

 further growth of the fruit, the cracks are extended, and finally several 

 may run together, making long irregular fissures (PI. I, figs. 1 and 2). 

 The flesh of the fruit is protected by the formation of a corky layer 

 in these cracks, but nevertheless the fruit itself presents a ragged and 

 irregularly cracked surface which, except in mild cases, renders it 

 unfit for market. 



A grayish water-soaked spot is the first indication of the disease 

 on the twigs of the current season. This soon becomes dark and later 

 is sunken. If there are a number of infections close together they 

 may coalesce, forming a rather large canker, which may persist, with 

 rather abundant flow of gum. Plate I, figures 5, 6, and 7, shows 

 advanoed stages of the disease on twigs. 



Usually in the Ozarks the first infections on leaves, twigs, and fruit 



occur in May, or sometimes even earlier. The disease does not 



t become conspicuous, however, until much later; in the Ozarks 



t tbout the middle of June in the case of leaves and twigs and about 



