DISEASES OF CORN AND SORGHUMS 257 



Smut. 

 General Characters. 



The corn smut, UsUlago ZecB (Beck) Ung. {JJ . zece-Mays, 

 U. Maydis) is widely distributed in the West Indies as in North 

 America, without assuming any serious proportions. It is dis- 

 tinguished by the swelhngs to which it gives rise on the leaves, 

 the ears, or the tassels, which may attain on the ears to an 

 enormous size. The pustules are covered at first with a greyish 

 envelope, which later bursts and reveals the masses of spores. 

 Any young and growing plant is liable to infection The leaves 

 are usually first attacked and the disease may be recognized 

 at an early stage by the whitish swellings there arising. 



Mode of Infection. 



When the spores are released a certain amount of direct 

 infection may take place, but the capacity of the spores to germi- 

 nate apart from the host plant on any moist nutritive material 

 very greatly increases the possibilities of infection. In rich soil, 

 for instance, or in manure heaps, a yeast-like growth takes place, 

 with the result that m}T-iads of conidia are formed, which are 

 easily distributed by the wind, and are able to start the disease 

 on any growing part of the corn plant they happen to reach. A 

 moist atmosphere facilitates infection, so also does the soft 

 growth induced by high fertility. Wide spacing reduces the 

 incidence of the disease. When the original spores do not attain 

 to a situation which favours their growth they remain dormant, 

 and are capable of germinating at any time, should the conditions 

 become favourable, during a period usually to be measured in 

 years. 



Prevention and Control. 



It will be seen that the deposition of smutted material in 

 cattle pens or manure heaps, or, since the spores can pass un- 

 injured through the alimentary canal, the feeding of diseased 

 plants to cattle, is a sure way of increasing and distributing the 

 disease. 



The idea that the smutted ears, of which cattle are very fond, 

 are unwholesome as food, has not been borne out by experiments 

 which have been made. 



Certain smut diseases, in which infection is confined to the 

 young seedlings, are capable of effective control by seed disinfec- 

 tion, but this is obviously not the case with the disease under 

 consideration. Still, spores may very well be present on the seed, 

 and where land is free from smut, and seed from an outside source 

 is being used, disinfection may be worth while, and may be carried 

 out as described on pp. 11 1-3. 



Where this species of smut already exists, the best means of 



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