42 Finger and Toe, and Wart Disease [CH. 
attacked. In such cases the disease will remain in the 
soil for four or five years, and if a cruciferous crop such 
as turnip is grown it is liable to attack. 
If it is necessary to use the dung for a cruciferous 
crop the roots should be boiled before they are fed. 
Diseased roots should not be put into the compost heap 
if the compost is to be used for the cruciferous crops. 
The disease very often appears on a small portion 
of a field and by taking measures at this stage it is 
easy to keep it in check. Sheep folded on such a field 
spread it over the whole unless the diseased portion 
happens to be the last portion folded. If such a patch 
is found it should be isolated from the rest of the field 
by means of hurdles, and the roots pulled and carted 
and treated as infected material. Care must be taken 
not to infect the whole field from the diseased portion, 
which should be limed as shown below. The disease 
may be spread by means of soil clinging to the feet of 
sheep, horses or men, and also by cartwheels and 
implements. Dirt should be scraped from these 
before tliey are used on other fields. The spores of 
Plasmodiophora brassicae are said to live for about 
five years. Consequently the rotation should be so 
arranged as to keep cruciferous crops, such as turnips, 
cabbage, rape, koh] rabi, and mustard out for at least 
six years. In the ordinary four course rotation turnips 
may be replaced by mangolds, potatoes, parsnips, etc., 
by which means turnips will not be taken until eight 
years after a diseased crop. Any crops other than 
cruciferous ones may be grown. It is extremely im- 
portant to keep the land free from the weeds of this 
order for they carry on the disease from year to year. 
Charlock is a great offender in this respect. By 
