CULTURAL DIRECTIONS 287 



time many of the infected plants will mature, although 

 the heads are usually small. Plants set in the field 

 in June or July seldom mature marketable heads if 

 attacked by club root. 



The spores of this disease are inclosed by protective 

 coverings that give them great vitality. It is not un- 

 common for the disease to recur in soils where crucifers 

 have not been grown for 10 or 15 years. With annual 

 tillage the spores soon become mixed with the soil and 

 the malady may spread over the field or the entire farm 

 or the community, and as no treatment of the plants has 

 been found effective, the grower must resort to preven- 

 tive measures. The following paragraphs relate to ways 

 of infestation or dissemination and methods of prevention : 



1. As young seedlings are most susceptible to attack, 

 great care should be exercised in selecting soil for the 

 seed bed. Affected plants should always be discarded. 



2. Rotation should be practiced, in which cruciferous 

 plants should not be planted more frequently than every 

 four years. 



3. The disease thrives best in acid soils. In Belgium 

 the calcareous soils were the last to become infested, and 

 lime is the best-known means of soil treatment, although 

 often unsatisfactory. The New Jersey Station reports 

 that 75 bushels of stone lime an acre gave as good re- 

 sults as larger applications. The lime should be applied 

 in the fall or at least several months in advance of 

 planting. 



4. Roots, stems and leaves from diseased fields should 

 be burned. If fed to stock or used for composting such 

 refuse will be a certain means of disseminating the 

 malady. 



5. In the purchase of all kinds of stable manures, the 

 grower should make certain that the stock has not been 

 fed plants which might cause infestation. 



