174 



Diseases of Econmnic Plants 



Fields known to be inf(^stecl should be relieved of sus- 

 ceptible crops by suitable rotation. Manure which may 

 have become infested in any way, 

 e. g. by feeding diseased crops to 

 stock, should be avoided. Drying 

 of the roots kills the causal or- 

 ganism, as does also exposure to 

 sunlight. Drying in the light is 

 therefore equivalent to surface dis- 

 infection and serves to reduce the 

 damage. Storage below 10° C. (50° 

 F.) gives best results. 



Drop (Sclcrotinia), see lettuce, 

 and Southern-blight (Sclerotium), 

 see pepper, are of some im- 

 portance. 



CASTOR-BEAN 



Wilt (Pseudomonas solanacearum) 

 (see p. 230) does considerable dam- 

 age, dwarfing the plants, causing 

 typical wilt, and finally death of 

 many plants. 



Gray-mold -'^ (Sclerotinia ricini, 

 Godf., Botrytis) of flowers, buds. 

 Fig. 94. — Carrot showing and pods in some cases affects 50 

 soft-rot; shaded portions to 90 per cent of the plants with a 

 represent the rotted part ^^t rot. Diseased tops should 

 of the root. Redrawn 

 after Jones. 



cut and Bordeaux mixture used. 



CAULIFLOWER. See cabbage. 



CELERY, PARSLEY, PARSNIP 



Late-blight --'' [Septoria petroselini Desm.). — In Italy late- 

 l)light was first reported in 1890; in the United States in 1891. 

 A loss of 1950 carloads and a money loss of $550,000 was 



