124 DISEASES OF TROPICAL PLANTS C H . 



on the leaves. They are not parasitic, but prevent the 

 plants from performing their ordinary physiological 

 functions. This is especially common where trees are 

 planted too close together or are not properly pruned. 

 Proper planting and care will in the great majority of 

 cases remove the necessity for treatment, but where it 

 is a serious factor it may be controlled by spraying or 

 washing the trunks and branches with strong Bordeaux 

 or by painting with the following mixture : dissolve 4 

 pounds soap in 10 gallons water, by boiling, and while 

 still hot add 4 pints crude carbolic acid. 



Epiphytes. These plants frequently become attached 

 to the trees, and while not directly injurious, are un- 

 sightly and frequently very annoying. They should be 

 removed by hand, and the trunks or branches washed 

 or sprayed with a 4 per cent to 6 per cent solution of 

 copper sulphate or rosin compound. 



Scaly Bark or Nail-head Rust. This is a disease of 

 the bark of the tree and the rind of the fruit of the 

 sweet orange, and has caused rather heavy losses in 

 Florida. It is due to a very small fungus known as 

 Cladosporium herbarium, Lk., var., citricolum, Lk. 

 On the young branches the disease appears as circular 

 or oval spots about J to J inch in diameter, slightly 

 elevated and of a rusty colour. As the disease advances 

 these spots become brittle, crack lengthwise, and 

 eventually break, thus giving a scale -like effect. In 

 some cases these spots are so numerous as to unite. 

 On the larger stems and trunk patches of rough shaggy 

 bark are produced. 



On the fruit the disease appears as brown sunken 

 spots or rings, which are at first yellowish or reddish - 

 brown, but eventually become dark. As the bark 

 cracks and flakes off, it gives openings for the entrance 

 of the wither-tip fungus (Colletotrichum gloeosporioides), 

 and finally causes the death of the affected part. The 

 disease is frequently confused with gummosis and 

 melanose. It can be controlled by grafting on immune 

 varieties, by heading back the trees, by painting the 



