424 THE FARMERS HANDBOOK. 



Fungus Diseases of Maize.* 



Ear-rot of Maize {Diplodia zeoe, Schw., Lev.). 



This fungus, producing Dry Hot or Ear-rot of maize, was first found 

 producing its spores on the dead stalks, and was looked upon as a saprophyte, 

 but it is now well known upon the living corn cobs. The disease is a serious 

 one, and appears to be spreading. 



The mycelium produced by the fungal threads is white in colour, and 

 much branched. The slender threads penetrate the young tissues of the 

 grains, cob, and husks. After the cob has become entirely involved, or the 

 growth of the parasite has been checked by the maturing of the corn, the 

 fungus enters upon its reproductive stage. The fructifications consist of 

 small black bodies (pycnidia), which develop in the husks, cobs, and more 

 rarely in the grains themselves. These pycnidia contain large numbers of 

 brown two-celled spores, and appear as minute black points slightly elevated 

 above the surface. They frequently become particularly well developed upon 

 the scales which surround the inner ends of the grains, and may be clearly 

 seen when the maize cob is broken across.' On the husks they usually occur 

 singly, but, on the cob, under favourable conditions, they may be grouped 

 together in masses. Diseased cobs, if left in the held under natural condi- 

 tions, may develop a black appearance. 



It is from the fungus when living upon dead tissue — the saprophytic stage — 

 that infection chiefly occurs, innumerable pycnidia crowded with spores 

 developing upon dead parts of the stem and cobs left in the field. The 

 spores, carried by the wind, lodge upon the developing cobs of the new crop, 

 and, if conditions are suitable, germinate and infect them. The conditions 

 most favourable to infection are a warm temperature and a certain amount 

 of moisture. The first of these conditions is usually present on the North 

 Coast, and the amount of moisture necessary must have a wide range, 

 as the rot has been prevalent in a dry as well as a wet season. Apparently, 

 therefore, the requisite conditions for the propagation of this disease may 

 be said to be always present there. The variations in its extent may be due 

 to the variability of the wind at the time when the cobs are in the most 

 susceptible stage, to the amount of spores available from old crops, and to 

 the power of resistance of the variety of maize grown. 



Treatment of the seed by pickling is of no avail as a preventive of 

 the disease. The source of infection must be attacked. 



(a) Old stems, old leaves, and maize stubble must, if the cobs have been 

 found to be infected, be gathered and burnt. Ploughing-in does 

 not destroy the spores, and corn planted on the same land may be 

 infected the following year. 



(b) Since Dry Rot is one of those diseases that can be carried by 

 the seed itself, it is of the utmost importance to secure seed free 

 from disease. As has been pointed out, infected cobs, if broken 

 sharply across, will disclose small black spots, particularly on the 

 scales at the base of the seed. 



(c) Rotation of crops is strongly recommended. 



(rl) Varieties of maize which are specially resistant to the disease are not 

 at the present time known, but possibly the most hopeful method of 

 combating disease lies in the selection of resistant varieties. 



* Compiled by Officers of the Biological Branch. 



