68 Cole Crops 



first indication of the disease. Affected leaves may later fall 

 off. Leaf petioles, leaf -sears, and stems of affected plants show 

 blackened dots, where the sap tubes are discolored. Practi- 

 cally all cultivated crucifers and many cruciferous weeds are 

 susceptible. Control: Seed disinfection is necessary. Formalde- 

 hyde solution made by adding 1 ounce of formaldehyde (40 

 per cent) to 2 gallons of water, or 2 teaspoonfuls to one pint 

 of water, may be used. Seed should be immersed for 15 to 20 

 minutes in the solution, the formaldehyde washed off in clear 

 water, and the seed spread out in a thin layer to" dry. Mercu- 

 ric chloride solution (1 to 1000) made by adding 1 ounce of 

 mercuric chloride to 7% gallons of water, or 1 tablet to 1 pint 

 of water, is also satisfactory. Seed should be soaked for 

 15 minutes, the mercuric chloride washed off in clear water 

 and the seed spread out in a thin layer to dry. It is desir- 

 able not to place the seed in direct sunlight and to stir them 

 at intervals during drying. A clean seed-bed, care in the 

 destruction of diseased material, and crop rotation are neces- 

 sary. 



Black-leg (Phoma lingam). — The disease develops on 

 leaves, stems and roots but characteristically attacks the stems 

 and taproot below the surface of the ground. In advanced 

 stages the dead areas are covered with tiny black fruiting 

 bodies. Conlrol: Same as' for black-rot. 



Yellows (Fusarium congludinans) . — Affected plants are 

 stunted, the leaves turning a pale yellow. Usually the symp- 

 toms appear earlier and are more severe on one side of the 

 plant, so that there is a warping and curling of stems and 

 leaves. There is a darkening of the vascular bundles of the 

 stem and the lower leaves of diseased plants drop early. Coiv- 

 trot: Seed disinfection (as recommended for black-rot and 

 black-leg) is Important to preyent the introduction of the fun- 

 gus, and a disease-free seed-bed is essential. Planting must 

 be into disease-free soil. The Volga and Houser are con- 

 sidered resistant. The Wisconsin Hollander is a resistant selec- 

 tion for the winter crop. 



