concluded that manure and commercial fertilizers 

 used separately and in different combinations did not 

 alter the amount of smut. This was also true when 

 chlamydospores were added to the manure. Maze and 

 Maze obtained similar results in Europe (215). 



Cultural practices. — Although the vigor of corn 

 plants may be greatly increased by good cultivation, 

 there is no clear evidence that there is a corresponding 

 increase to the prevalence of smut. Selby and Hickman 

 (298 1 obtained no effect on prevalence of smut fol- 

 lowing deep and shallow cultivation, whereas Clinton 

 (60 i reported an increase in the amount of smut with 

 repeated tillage of the soil. 



Kyle I 194 > found that "level-planted"' corn de- 

 veloped more 'smut than "furrow-planted'' corn. He 

 attributed this to differences in vigor of plants. Wal- 

 ter ('351 ) cultivated corn plots by 3 different methods 

 for 3 growing seasons. In spite of differences in vigor 

 of plants, the smut was no more severe in the culti- 

 vated than in the noncultivated plots. 



Spraying. — Kellerman (177), in 1891, was perhaos 

 the first to claim partial control of corn smut by 

 spraying the plants with a fungicide. Smut infection 

 was reduced from ll f ; to ~, r ', . Stuart (329), in 1895. 

 and Arthur and Stuart (5), in 1896. reduced the smut 

 with Bordeaux mixture and ammoniacal copper 

 carbonate. The more frequent the application of spray 

 the greater the reduction in smut. Ten sDrays with 

 the Bordeaux mixture decreased smut by 72 f r. Their 

 results do not indicate whether the yield of grain was 

 increased. 



Potter and Melchers (266) concluded that partial 

 smut control with fungicidal sprays caused spray- 

 injury to the plants. A decrease in prevalence of smut 

 also resulted in a corresponding decrease in yield. They 

 believed that chemical injury reduced vegetative activ- 

 ity of the host and hence a decrease in smut infec- 

 tion and a reduction in grain yield. 



Pepper and Haenseler (253) eliminated from half 

 to all ear smut by the use of dusts containing either 

 rotenone or nicotine. The insecticides were actually 

 used to control the European corn bo-er. but Baskin 

 (11) found no association between the prevalence of 

 European corn borer and the incidence of smut. Baskin 

 also found that certain insecticides and fungicides 

 reduced smut infection: Zerlate i zinc dimethyldithio- 

 carbamate i and Fermate i ferric dimethyldithiocarba- 

 mate i were most efficient. These results suggest that 

 insects may be important agents in dissemination of 

 inoculum, in creating avenues of entrance for the 

 pathogen, or both. Unfortunately, very little research 

 has been done on the role of insects in relation to 

 epiphytotics of corn smut. This subject is in need of 

 research. 



Since much of the smut infection apparently occurs 

 through the leaf whorl which often harbors chlamydo- 

 spores and sporidia of U. maydis, proper application 

 of a good fungicide should be an effective means of 

 reducing smut infection. Naturally, the compound 

 used should be nonphytotoxic to the corn yet inhibit 

 the germination of spores or kill the promycelia. The 

 material used by the early investigators did not possess 

 these properties. 



The use of antibiotics also should not be over- 



looked. Bamberg's experiment with living bacteria 

 suggests control by biological methods (7. 8). Miss 

 Benigni (18) claims to have induced temporary im- 

 munity by vaccination. 



Biological control. — Microbiological antagonism may 

 play a very important role in limiting the prevalence 

 of U. maydis in nature. Fungi and bacteria are often 

 common cohabitants in smut galls. They are also 

 commonly associated with U. maydis in the axils of 

 leaves along with dirt and plant debris. Some smut 

 galls become thoroughly infested with bacteria and 

 species of Penicillium, Aspergillus, Mucor, Trichothe- 

 ciian, and other fungi. To what extent these are 

 parasitic on smut spores is not known. Deckenbach 

 7h i stated that Oospora virticillioides Sacc. is para- 

 sitic on U. maydis. Sometimes, the consistency of smut 

 galls is greatly modified by the presence of bacteria 

 and the percentage of germination of the chlamydo- 

 spores may be very low. In 1930. Bamberg (&) 

 isolated a bacterium from corn that destroyed colonies 

 of U. maydis. Later, he found additional bacteria 

 that were also antibiotic to U. maydis. When the bac- 

 terial suspension was introduced into the gall, chlamydo- 

 spore formation was inhibited. The mixing of bacteria 

 with sporidia before injection into the corn plant 

 materially reduced the amount of infection. Miss John- 

 son (168) isolated 4 species of bacteria, including a 

 Myxobacterium, that were antibiotic against V. maydis. 



In 1948. Cercos (46) described a new species of 

 bacterium. Flaiobacterium ustilagophagum, which was 

 very antibiotic to U. maydis. From Bacillus subtilis, 

 Cercos and Favret (47) isolated an antibiotic substance 

 called "fungocin." It was lethal in small dosages 

 to V. maydis growing in culture. 



Antagonism is not one-sided, as U. maydis also 

 produces antibiotics that inhibit the growth of other 

 organisms. Haskins (126) found that when U . maydis 

 was grown in liquid culture it produced 2 antibiotic 

 substances: one of these was active against several 

 bacteria, the other against several fungi. Haskins (126) 

 designated these as "Ustizeain A and B": later. 

 Haskins and Thorn i 127) changed the term to 

 "Ustilagic acid." 



One must assume that in nature V. maydis, particu- 

 larly the saprophytic stage, is subject to constant 

 biological warfare. This struggle must be especially 

 acute in areas of rich organic material, either in the 

 soil or in the leaf whorls. This may be one of the 

 reasons why smut is most destructive in the semi- 

 arid regions. The subject of biological control is very 

 much in need of basic research. 



Development of resistant varieties. — Varietal resist- 

 ance. — At present, the only feasible and practical 

 means of controlling corn smut is by growing resistam 

 varieties. It has been known for a long time that 

 varieties of corn differed in their susceptibility to 

 smut. Hitchcock and Norton (143 ». in 1396. observed 

 considerable differences in percentage of smut on 46 

 open-pollinated varieties of corn. No variety was 

 immune. In 1900. both Clinton (60) and Arthur and 

 Stuart i 5 I reported that sweet corn was especially 

 susceptible to smut. Clinton 1 60 1 believed that 

 varieties late in maturity and rank in growth were 

 most likelv to become smuttv. In more recent times. 



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