194 Diseases of Economic Plants 



the disease. All dead stalks, leaves, etc., should be collected 

 and burned in the fall. 



Verticillium wilt {V erticiUium albus (Preuss)). — This wilt 

 is due to stoppage of the veins by fungous growth, and the 

 chief symptom is wilting of the leaves, followed by death of 

 the stem and leaves. Sections of the rootstock reveal a 

 yellowing of the water ducts and veins, which contrasts 

 strongly with the normal white of a healthy plant. 



The disease is largely confined to the older, less vigorous 

 roots. It is advisable to remove and dry the infected 

 roots and to replace the soil of infested beds with new, 

 healthy soil. Soil disinfection should be employed if 

 practicable. 



Black-rot (Sclerotima sviilacina Dur.). — Black, warty 

 sclerotia upon the root indicate this disease. The roots are 

 very black, but upon drying, bleach somewhat. In old age 

 this blackening may extend to the center of the root, which 

 becomes wet, spongy, and pliable. The disease remains in 

 the soil some years after infestation. Sick roots should be 

 removed and burned if not marketable. Treat also as 

 for wilt. 



Soft-rot. — This rot occurs widely and causes large loss. 

 The root decays rapidly, is sticky and ill smelling. The 

 leaves turn red and yellow and soon die. A rot ^^'' due to 

 Phytophthora cactorum (C. & L.) Schr. is reported as causing 

 a loss of 20 per cent in some beds in New York. Damping-ofif 

 {Corticium) is largely prevented by thorough ventilation, and 

 the avoidance of excess of moisture in soil and air. Stirring 

 the soil to hasten drying, aids. See p. 19. Leaf-anthracnose 

 {Pestalozzia funerea, Desm.) is destructive to young plants. 

 It appears as a black, velvety growth at the bases of the 

 leaves and flower stalks, causing them to die and fall off. 

 Spray as for blight. Thielavia-root-rot (Thielavia hasicola) 

 is especially harmful to seedlings, resulting in sudden wilting, 

 which causes them to bend over and dry up. The fine roots 

 are affected as are the roots of tolxacco. Dark brown, dry 

 lesions are also produced on the roots by a Ramularia. 



