DISEASES OF CORN AND SORGHUMS 259 



The conidia are spindle-shaped, pale olive, 5-8 septate, 

 80-140x20-26 micr. 



Prevention. 



Protection against the disease is to be secured by rotation 

 of crops, avoiding the use of manure made from diseased material, 

 or by the adoption of resistant varieties. 



Dry Rot. 



Several fungi are capable of infesting the ears of growing 

 maize, causing the adhesion of the husks and a development of 

 mould on the grain. In North America a very large proportion 

 of this type of injury is due to the fungus Di^lodia Zece. In some 

 years the disease results in a very serious decrease in yield. 

 Notable losses are also reported from South Africa in connection 

 with the same fungus, and there is strong suspicion that paralysis 

 and death of stock in that country results from feeding on the 

 diseased cobs. The idea that pellagra is similarly caused is now 

 discredited. 



So far as the writer is aware, corn in the West Indies is subject 

 to but little loss from the type of disease under discussion. 



Appearance of the Disease. 



In the early stages of infection there is little external appear- 

 ance of disease. The first sign is the premature fading of the 

 bright green of the outer husks to a yellowish colour, while the 

 inner husks may be more or less browned. In the ear the 

 fungus is first visible around the tips of the kernels if these are 

 removed. Later the ear loses much of its weight, becomes 

 mouldy with the development of grey mycelium around the 

 kernels, and these appear dull and dry. The most distinctive 

 sign of the presence of Diplodia is the early development of the 

 minute black pycnidia on the scales which surround the inner 

 ends of the kernels. Pycnidia can also be found on the husks, 

 and in advanced cases on the grains themselves. On old stalks 

 they can be seen as black specks under the rind near the nodes, 

 or breaking through and discharging their spores. 



Mode of Infection. 



It has been claimed that the common method of infection is 

 from the soil, the fungus entering by way of the roots, working 

 up the stem, and entering the ears and kernels from within. 

 On the other hand, typical cases can be readily produced by 

 placing spores on the silks or under the outer husk at the base of 

 the ears. Little or no infection takes place from ear to ear in the 

 same season, the period of susceptibility being apparently a short 

 one, confined, so far as external infections occur, to the period 

 when the silks are exposed. 



