Cole-crop Diseases 



67 



rot hy means of rotation and special treatments, destroying 

 the cabbage-worm as soon as it appears, — these are essen- 

 tials in cabbage growing. 



One ounce of cabbage seed contains over 8,000 seeds, hut 

 not more tban one-third or one-lialf of these seeds may be 

 expected to make good plants. Early varieties are set 18 x 24 

 inches, or 24x24 inches (about 12,000 plants to the acre); 

 late varieties 2x3 feet (about 7,000 plants). Four to six 

 ounces of seed are usually required for an acre. The yield can 

 be estimated from the number of plants to the acre, as a 

 plant produces only one head. The heads of early varieties, 

 which are set close, weigh from 2 to 4 lbs., of the late varieties 

 5 to 6 lbs. Due allowances must always be made for uneven 

 crop, insect depredations, and other losses. For early cab- 

 bage, 8.000 heads to the acre are considered a good crop. In 

 field culture, the yields run 10 to 20 tons to the acre, with 15 

 tons as perhaps a fair average in the hands of good men ; 

 25 tons, and even more, are sometimes secured. 



Clubroot {Plasmodiophora hrassicre). — The most striking 

 symptom of clubroot in the field is a flagging of the leaves 

 of affected plants on sunny days. Such plants regain their 

 normal appearance overnight, but soon wilt again. The roots 

 of diseased plants show characteristic malformations or swell- 

 ings w^hicli frequently attain large size. Cauliflower, turnips, 

 radishes, shepherd's-purse, wild mustard and other related 

 plants are affected. Control: A clean seed-bed is essential. 

 Slaked lime at the rate of about 75 bushels to the acre applied 

 every few years is advisable if the disease has appeared in a 

 field, since an alkaline reaction is unfavorable to the develop- 

 ment of the organism. This should he applied the fall pre- 

 vious to planting. Diseased plants should be destroyed by 

 burning. A long rotation, during which cruciferous weeds 

 and cultivated crucifers are not permitted to grow, is 

 important. 



Black-rot {BoGterium campestre) . — The yellowing of af- 

 fected leaves followed by a blackening of the veins is the 



