1 9-2-2.] 



DlSExiSES OF THE SWEDE CROP , 



1095 



The swede crop usually follows oats in the rotation, but some- 

 times potatoes are the preceding crop. It was remarkable last 

 year that where swedes were grown after oats there was more 

 finger-and-toe in the crop than in those crops which followed 

 potatoes. Indeed, the only crops of swedes last year where no 

 finger-and-toe was found, were grown on land which carried 

 potatoes the previous year. 



It is also noticeable that there is always more finger-and-toe 

 to he found along the headlands, in the vicinity of gates, and 

 in damp portions of the fields, than in other parts of the field. 

 Portions of diseased roots and contaminated soil are liable to be 

 carried to gates and headlands on boots and wheels, and these 

 would infect the soil very heavily, but in addition such places are 

 of necessity trampled and puddled, and, consequently, the soil 

 is not so thoroughly aerated as in other parts of the field. It 

 is possible, therefore, that thorough cultivation and aeration 

 of the soil would tend to prevent the disease— JPossibly this may 

 account for the fact that swedes following potatoes are freer 

 from finger-and-toe than swedes following oats, since- with a 

 crop of potatoes the soil receives more cultivation. 



It would seem that early sowing combined with a good 

 seed bed also tends to check the disease. In 1921 most 

 crops in this district were sown early, with the soil in really 

 good condition, and it would appear that the few crops in which 

 the disease was severe were sown late. The most seriously 

 diseased crop observed was sown about the first week in August 

 and 90 per cent, of the plants were affected, the roots being 

 small and stunted. This crop was a complete loss. 



Owing to the slightness of the attacks last season the actual 

 money losses sustained by the farmers were almost negligible; 

 this is due probably to the dry summer and early sowing in a 

 good seed-bed. In an average season the losses are much 

 heavier. The damage caused by finger-and-toe in this district 

 in an average season is much greater than the damage caused 

 by wart disease of potatoes. The protective measures for 

 finger-and-toe, and the amount of lime or chalk required, are 

 fully dealt with in Leaflet No. 77. 



Dry Rot. — In addition to mildew and finger-and-toe, swedes 

 are sometimes affected by the disease known as dry rot. This 

 disease was first described in 1900 by Professor M. C. Potter.* 

 The disease is caused by a minute fungus, Phoma napo-brassicae, 

 which attacks the roots and forms a soft, brown rot, but one 



* This Journal. Vol. VI, pp. 448-456. 



