3i3 



Brown-rot of Swedes. 



The plants show signs of wilting, and the heads become dwarfed 

 and distorted, as the disease proceeds from certain centres of 

 infection. 



The precautions mentioned above apply equally to cabbages, 

 and very serious destruction to this crop has been traced to 

 infection spread in this manner. It is advisable for seed-beds 

 to be changed each year, and it is better not to employ soil upon 

 which a cruciferous crop has been recently grown. In one case 

 of extensive damage the same plot of land had been used for a 

 seed-bed for several years, and cabbages had been planted on 

 the same land for seven years in succession. 



The removal of affected leaves at frequent intervals and their 

 subsequent destruction has been recommended, and this treat- 

 ment was considered to have met with success, but more 

 recently Stewart and Harding have shown by a series of 

 practical field experiments that leaf-removal is worthless as a 

 method of controlling the disease, and that it considerably 

 reduced the yield per acre. This treatment would obviously be 

 valueless where the infection commences through the roots. 



It seems probable that our greater immunity from this 

 disease in England may be due to a better system of rotation 

 of crops, and also possibly to the temperature in this country 

 not attaining the high summer temperature of America — 80 

 degrees to 90 degrees Fahrenheit or higher — which Smith has 

 shown to be the most favourable for the growth of this germ, 

 particularly when accompanied by a damp atmosphere. 



M. C. Potter. 



Description of Plate. 



Transverse section of a Swede attacked by Brown-rot, from a field at Cockle 

 Park. On the upper left hand corner the disease has considerably advanced into the 

 interior, while the brown dots extending round the periphery indicate an early stage 

 of attack in the vascular bundles. 



