DISEASES OF CULTIVATED PLANTS 543 



When the plants are infected at the seedling stage they are usually 

 killed before the season is half over, and the infected areas may be 

 seen entirely bare of cabbage. The swollen, contorted roots, which 

 have robbed the plant of its food material, begin to decay in the soil 

 in the latter part of the season and continue the process of decay, 

 aided by frosts and soil bacterias, so that nothing of them is seen the 

 following spring. 



There is but one agent responsible for the club root disease. 

 This is known as Plasmodiophora brassicse, an organism belonging to 

 the lowest orders of plant life. 



It appears that, so far as experimental work has gone, the use of 

 lime is distinctly beneficial in combating club root disease in the 

 field, and that the after effects of the lime, as shown on the plot where 

 it was applied two years previous to the experiments, are quite 

 marked. Acid phosphate was of little use in combating the disease. 

 Whether this is due to the slightly acid condition which it gives the 

 soil, or w'hether it is due to the fact that the phosphate is favorable 

 to the growth of the organisms, is not ascertained. Stable manure 

 brings conditions which are decidedly favorable for the spread of the 

 disease, because of the large amount of organic material which it in- 

 troduces into the soil. 



Recommendations. 1. Avoid introducing any material into 

 the field which may carry the germs of the club root from diseased 

 fields. Guard especially against diseased soil and diseased cabbage 

 plants. 



2. Practice crop rotations which will allow at least three years 

 between crops of cabbage, rutabagas, or turnips. 



3. Apply stable manure to the crop which precedes cabbage, 

 but not to the cabbage crop itself. If acid phosphate is applied the 

 same rule would hold. 



4. Lime will more successfully counteract the club root dis- 

 ease than other substances. Apply it at the rate of 100 bushels or 

 more per acre one or two years previous to planting the cabbage. 

 (Vir. E. S. B. 191.) 



Fusarium Wilt or Yellows of Cabbage. This trouble is known 

 as yellows this term being applied because of the external appear- 

 ances. In diagnosing the disease, this color characteristic is the first 

 symptom to be relied upon. Later, a stunted growth, \vith a tend- 

 ency of the lower leaves to drop at the lightest touch is further evi- 

 dence of the disease. To the keen observer these symptoms may bo 

 detected in the seed bed previous to transplanting. Plants which 

 show the symptoms in the seed bed, upon being transplanted, make 

 no further growth, they simply wilt, turn black, and the lower leaves 

 usually fall off. 



After setting out, the healthy plants are attacked at all stages 

 of their growth. In the older and later infected plants, the prelimi- 

 nary symptoms are similar to those in seedlings; yellowing of the 

 lower and outer leaves takes place; these leaves later drop, turning ;i 

 drab color, the lowest first, being followed successively at different 

 times by others in their order. 



