8o Stinking Smut or Bunt in Wheat. 



Conditions favouring the Diseask. 



There is no doubt that bunt is more prevalent in some years than in others. 

 In the season of 1898 it was so prevalent in Victoria that it was estimated to 

 have caused a loss on the year's crop of £50,000. In 1908, with a record har- 

 vest, there were certain districts, such as the Wimmera, where the value of 

 the crop was considerably reduced from this cause alone. Ten years ago, the 

 treatment of seed-wheat for smut was neither so general nor so well carried 

 out as it is now, although farmers asserted that every precaution had been 

 taken in the treatment, and even now there are some who neglect it altogether, 

 or do it in a slipshod manner. 



Heat and moisture are the two controlling factors in its development, 

 especially the latter. It is generally considered that less moisture is required 

 to germinate the smut spores than the wheat, on account of their much smaller 

 size, hence it is a common practice in some districts to sow the seed unpickled 

 in a dry seed-bed, but to pickle it after rain. In the one case, the insufficient 

 moisture is likely to start the growth of the smut spores before the wheat, 

 and in the absence of a host-plant, the germ-tubes shrivel up and die, while 

 in the other, there is every probability of both germinating at the same time 

 and infection is sure to occur. A cold and wet period immediately after sow- 

 ing is more favorable to the growth of the bunt than of the wheat, and the 

 tissues of the young plant, being soft and tender, there is often a larger pro- 

 portion of bunt than usual. But in discussing the relations between the 

 nature of the season and the prevalence of bunt, there are no definite experi- 

 ments to guide us. 



Effects upon the Crop. 



When the smut appears in a crop, the farmer generally considers his loss 

 as being entirely due to the ears destroyed by the fungus and to the deprecia- 

 tion in price per bushel for the remaining sound wheat, but it has been shown 

 by Bolley3 particularly, that smutted ears are only an indication of more 

 widespread damage. Thus it was found that in stools with only one or a few 

 ears affected, the smut fungus was in all the straws, even when the heads 

 were sound. Further, in untreated wheat paddocks where only about one- 

 third or one-fourth of the crop had actually smutted heads, it was difficult to 

 find a stool or a straw free from the fungus, explaining why the crop was 

 materially reduced beyond the evident indications. Then the growth of the 

 straw may be seriously interfered with, as well as the formation of the heads, 

 for it has been observed that on stools bearing smutted ears there are often 

 several unheaded straws. Kuehn^ even found that, where smut infection 

 was very bad, youngr plants might die back completely. Where the straw 

 is completely formed, the heads may still be poor, for just at that period when 

 the grain is about to be formed, if the fungus is present, there is Hkely to be 

 a shortage of supplies. As we remarked in connexion with the rust-fungus, 

 " In the actively growin:T and feeding period of the plant's life, it is apparently 

 able to provide for the wants of the fungus as well as its own, and therefore 

 its vitality is not seriously alfected. But when the second period of forming 

 and ripening the seed arrives, when feeding is gradually ceasing, and the ac- 

 cumulated materials are being transferred to the seed, then the fungus draws 

 upon the plant's capital, crippling its energies, and checking the movement 

 of the food materials to the seed." If the fungus filaments are not sufficiently 

 robust to give rise to the spore-forming hyphae and invade the grain, they 

 are still capable of diverting food material from its natural destination — the 

 ear. 



