Black Dry Rot in Swedes. 



27 



good many plants had died from the attacks of Phoma, but I 

 did not see a single specimen suffering from the black 

 dry rot that had carried off every root a few yards away. 

 The soil and subsoil were examined, but there was nothing to 

 account for the sudden cessation of the disease, except the 

 fact that the diseased portion had been limed, and that the 

 sound portion had not ; and from the appearance of the field 

 and the evidence collected on the ground, I am satisfied that 

 lime encouraged the disease. 



The farm changed tenants some years ago, and particulars 

 of the application of lime could not be obtained, but it was 

 known that lime had been applied seven or eight years 

 previously (probably before ploughing the land for the last 

 turnip crop), and from the fact that lime was provided by 

 the estate, it was inferred by the present tenant — who based 

 his conclusions on the disposition of his predecessor — that 

 the dressing had been a liberal one, probably 5 tons per 

 acre. 



From the isolated character of the turnip field, from the 

 fact that both swedes and turnips (sown at different times) 

 were diseased, and also from the fact that a part only of each 

 row of turnips was affected, it seems quite clear that the 

 crop became infected by the organism producing black dry 

 rot through the soil, and there is evidence that the cause of 

 infection was the dung used. The field itself has not been in 

 roots for years, and the soil can hardly have been tainted ; the 

 dung, on the other hand, was made from a crop that was, in all 

 probability, diseased. 



The first symptom of disease is a dark, almost black, spot 

 in the centre of the turnip. When I showed these spots to 

 the farmer he remarked that most of his last year's crop had 

 been "like that " when lifted, but that they had not got any 

 worse, and had all been consumed. The attack, therefore^ 

 which came on late in the season, and did little damage last 

 year, appears to have been the cause of the disease that 

 ruined this year's crop. 



Until the soil has been analysed, and the life history of 

 the micro-organism responsible for the rotting has been in- 

 vestigated, it is impossible to say precisely why infected 



