254 THE CHIEF SOUTHERN AGRICULTURAL CROPS 



Any injury to an orange tree is apt to result in a 

 flow of gum. As we have seen, it is a symptom in 

 both of the above diseases. There are other obscure 

 diseases of the orange in various countries that are 

 accompanied by the exudation of gum. These are 

 collectively known under the name of "gummosis," 

 but none of them have been sufficiently studied to be 

 really understood. 



Scab (Cladosporium) is a fungous disease causing 

 blisters and distortions on the leaves and young 

 fruits of lemons and sour oranges. It does not attack 

 the sweet orange and usually does no material harm 

 to grape fruit. Sour orange seedlings in the nursery 

 are often so badly attacked by it as to retard their 

 groAvth and leave them in poor condition for budding. 

 It can be successfully prevented by spraying with 

 Bordeaux mixture. 



Sooty mold QFiimago C'ltri^ often erroneously called 

 Meliola Citri) is a fungus forming a black, crustlike 

 coating on the fruit and leaves. It is not a parasite, 

 and is by no means confined to the orange, but it is a 

 " honey dew " fungus growing on the sweet ex- 

 udations of certain aphids and scale insects. It 

 greatly injures the appearance, quality, and market 

 value of the fruit, and if abundant lowers the vitality 

 of the tree by obstructing the functions of the leaves. 

 It can be entirely prevented by keeping the trees 

 clear of the insects which furnish its food supply. 

 This, however, is often not an easy matter. 



The rust mite (^Pliytoptus) is very abundant in the 

 West Indies and Florida. It is not a true insect, but 

 is related to the spiders and is so small as to be in- 



