DISEASES OF CROPS 209 



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rot at the stem end which can be detected by a pressure of the finger even 

 though there may be no discoloration. The presence of scale insects and 

 warm, damp weather tend to increase the disease. 



This organism also causes the disease known as melanose of the fruit, 

 twig and leaf. This form of the disease appears as a raised brownish area 

 forming dots, lines and crosses, varying from yellow to brown and black. 

 The cutting out of the dead wood is an important factor in the control of 

 this disease. 



Other Rots (Penidllium italicum, Wehm., and P. digitatum [Fr.], 

 Sacc.). These rots are covered by the fungus and appear as blue moulds. 

 They are the causes of heavy losses in transportation. The fungus enters 

 the fruits through slight wounds and therefore the fruit should always be 

 handled carefully. 



Sooty Mould (Meliola camellia [Catt.], Sacc.). In this case the 

 fungus covers the fruit with a black velvety coating which can usually be 

 removed. It is not nearly so serious as some other diseases. It really 

 grows on the exudations (honey dew) of plant lice and its control depends 

 on their destruction. 



Black Pit of the Lemon (Bacterium citriputeale, Sm.). This disease 

 appears as circular or oval, well-defined, reddish-brown, brown or black 

 spots or pits on the fruit. They are caused by bacteria which gain entrance 

 through wounds. 



Anthracnose or Wither Tip (Colletotrichum glceosporioides, Penz.). 

 This disease attacks the young leaves, twig tips and fruits. It causes a 

 yellowish spotting of the leaves, a withering and dying of the new shoots 

 and canker-like spots on the fruit. It is one of the most common diseases 

 of the citrus fruits. 



Scab (Cladosporium citri, Mass.). This very common disease attacks 

 leaves, twigs and fruits, causing prominent warty or corky outgrowths. 

 The leaves are frequently twisted and twigs are frequently cracked. 



Canker. This is a comparatively new disease in America and there is 

 some difference of opinion as to the cause. It is very destructive and a 

 very vigorous campaign is being made against its spread. It occurs on 

 leaf, twig and fruit, causing dead, circular spots which are usually raised. 

 They are light-colored when young, but become brown and corky and fre- 

 quently marked with small cracks. 



Other important diseases of the citrus fruits are the scaly bark or 

 nail head rust (Cladosporium herbarum var. citricolum) of Florida, the 

 citrus knot (Sphceropsis tumefadens, H. and T.) of the West Indies, and 

 the gummosis, which is very widely distributed. 



Treatment of Diseases of Citrus Fruits. So much progress is being 

 made in the study of these diseases at this time that it is inadvisable to 

 attempt a discussion as to treatment. Those interested in these diseases 

 should consult with the agricultural experiment station in the state in, 

 which the disease occurs. 



