434 Diseases of Economic Plants 



point of attachment of the leaves, and later it passes to the 

 stem, causing soft rot and shrinking of the outer parts. After 

 defoliation the disease spreads slowly toward the base of the 

 stem. Infected parts should be burned. 



SNAPDRAGON 



Anthracnose "*■" (Colletotrichum antirrhini Stew.). — This 

 disease which often ruins the crop is the most destructive of 

 this host, both under glass and in the open. It attacks plants 

 of any age, producing on the stem elliptical sunken spots, 

 5-8 mm. long, and on the leaves circular dead spots. These 

 are at first dirty white with narrow brown margins; later 

 acervuli appear in the center, at first brown, then black. 

 Diseased plants show numerous, dead, hanging leaves. The 

 stems or lateral shoots may be girdled, killing the parts 

 beyond. 



It is recommended to use only healthy plants for cuttings 

 and to clean up and burn all diseased refuse. The cuttings 

 should be sprayed when well rooted and repeatedly until 

 transplanted. Excess of water should be avoided and 

 thorough ventilation provided. 



Leaf-spot '"^ (Phijllosticta antirrhini G. & A.). — Circular, 

 brown or black spots about one centimeter in diameter, 

 usually marked by concentric ridges, appear on the leaves. 

 Lesions on the petioles cause death of the leaf and infection 

 of the axils. Stem lesions may be 2 or 3 cm. long and 

 eventually girdle the stem, resulting in death of all distal 

 parts. Young plants die from typical damping-off. Bor- 

 deaux mixture is recommended for forms of the disease 

 other than damping-off, which must be met by soil dis- 

 infection. 



Rust ^''^ (Puccinia antirrhini D. & H.). — This rust has 

 recently appeared in greenhouses in destructive form. Dis- 

 eased stock should be excluded and sub-irrigation adopted if 

 possible. 



