26 



spores from a pure culture should be applied to the epidermis, 

 after which a moist atmosphere is necessary. 



DISTRIBUTION OF THE DISEASES. 

 The diseases known as wither-tip, anthracnose, leaf-spot, and 

 canker extend through a large portion of Florida, the West Indies, 

 South America, Australia, and Malta, and it seems probable that 

 they bccur in all parts of the world where the orange is cultivated, 

 especially in the more humid regions. The drier regions are more 

 exempt from leaf and branch inhabiting fungi. 



GENERAL METHOD OF ATTACK. 

 The initial lesion is usually at the tip or an edge of a leaf. 

 More rarely is a leaf attacked at the midrib or some other interior 

 portion. The part attacked becomes light green, then turns brown. 

 Then the acervuli form ; at first light brown, then dark brown or 

 nearly black. They may develop on either surface and in various 

 arrangements. 



EXTENT OF INJURY. 



All sizes of trees, from those located in the nursery (even seed- 

 lings in the seedling beds) to the oldest trees in a grove, are 

 subject to attack. Budded trees less than a year old are rarely 

 attacked except in the leaves. Where such infections are allowed 

 to remain on the trees the diseased area extends into the growing 

 twigs and causes the typical " wither-tip." In such cases the 

 tip dies back for a distance, or the disease may go as far as the 

 trunk and then stop. A bud below the diseased portion then 

 pushes forward, but unless preventive measures are used the 

 second sprout withers back like the first. In this way the disease 

 may prevent the tree from making any growth, and even kill it in 

 four or five years. 



The initial attack in older trees is the same as in trees in the 

 nursery rows. The fungus gains entrance to the tissues of the 

 leaf and from this grows down into the fruiting twigs. This cuts 

 off much of the younger growth in severe cases and thus prevents 

 blooming to a large extent. Such cases are frequently mistaken 

 for blight, but a more common error is to attribute the injury to 

 die-back. It may be readily distinguished from blight by the fact 

 that only small twigs die off, and these do so without any wilting 

 of leaves. Even the leaves that are so badly diseased that they 

 fall do not wilt, while in the case of blight the leaves wilt with no 

 visible sign of injury. It may be distinguished from die-back by 

 the absence of multiple buds, of gum pockets, or of dark excres- 

 cences. One or more of these characters always accompany die- 

 back. Die-back twigs may be attacked by this fungus, but in such 

 cases wither-tip must be regarded as the secondary disease. 



This disease may be also present in a blighted tree. Any 

 agency that lowers the vitality of a tree, whether fertilizer, weather, 

 or condition of soil, predisposes it to an attack of wither-tip, but 

 trees that are in the most healthy condition possible are also at- 

 tacked when exposed to infection. The damage caused by this 



