200 The Principles of Vegetable -Gardening 



tial that the crops of a rotation be of such different 

 kinds that the same kinds of insects or fungi will not 

 thrive on them. Wire worms are starved out by a 

 short and quick rotation. If the land is infested with 

 them, the best thing to do, therefore, is to put the 

 land into other crops and other uses, not to try to kill 

 them by poison baits. They are usually most serious 

 in those lands which have been laid down to grass for 

 some time. The same thing may be said of the white 

 grubs, which appear in grass lands. They are rarely 

 troublesome when short and thorough rotations are 

 used. 



2. If the land becomes seriously infested with any 

 one pest, it is best in general to discontinue, for' two 

 or three years, the growing of the crop on which they 

 live. This ordinarily is cheaper and quicker than to 

 endeavor to destroy the pest by direct means. This is 

 well illustrated in the case of the club -root of cabbage 

 and cauliflower. This disease may be lessened some- 

 what by thoroughly dressing the land with lime; but 

 it is usually cheaper, and always more effective, to 

 cease the growing of cabbage, cauliflower and turnips 

 for a time, and to grow other kinds of crops on the 

 land. It will usually be cheaper for a man to buy his 

 home supply of cabbages than to attempt to grow them 

 on land which is badly infested with either the club- 

 root fungus or the cabbage maggot. 



In 1894, soil from a cabbage field which was seriously in- 

 fected with club -root, was sown in the hills of a cabbage field 

 at Cornell University. The soil was clay. The plants were 

 ruined by the disease. In 1895 cabbages and turnips were grown 



