Gladiolus Studies — II 257 



There are at least three important diseases of the gladiolus, namely, 

 hard rot, dn,' rot, and scab. The first two are characterized b}' necrotic 

 lesions of various sizes in the corms, the diseased area blending more 

 or less gradually into the healthy tissue. Scab lesions have a sharp line 

 of demarcation, a distinct ridge being formed around the border of the 

 depression. The surface of the depression has a somewhat metallic luster. 

 In the older scab spots there is a cavity beneath the metallic film, appear- 

 ing as if eaten out by some insect. 



The lesions of hard rot and dry rot are usually small in the autumn, 

 when the corms are dug. The diseases advance while the corms are in 

 storage, until by spring many corms are reduced to dry mummies. Scab 

 lesions do not enlarge after the corms are placed in storage. 



Hard rot and dry rot are caused by fungous pathogenes whose life 

 histories do not materially dift'er. The two fungi live over winter in the 

 corm and are thus carried to the soil at planting time. The fungi do not 

 grow from the old corm directly into the offspring, but either grow out 

 into the soil, whence they attack the corms, or else work along the sheath- 

 ing leaf bases. In the majority of cases a diseased corm may be expected 

 as a result of planting one that is diseased. 



The cause of the scab disease is unknown. Attempts to connect some 

 fungus with the diseased areas on the corms have failed. The lesions 

 may be due to the attacks of certain insects, such as wireworms or milli- 

 pedes, but no experimental data are at hand to prove or disprove this 

 suggested possibility. 



Various soil and corm treatments have been used in an effort to control 

 the hard rot and the dry rot of the gladiolus. Corms have been treated 

 with formalin, corrosive sublimate, hot water, dry heat, and so forth, 

 at strengths as high as the corms would permit without injury. None of 

 these treatments have proved effective. Soil has been treated with lime, 

 acid phosphate, sulfur, lime and sulfur, and iron sulfate, in strengths as 

 high as the grower could afford to use them, without protecting the 

 corms from the attacks of these fungi. 



The selection of healthy corms, which are planted in soil in which no 

 gladioli have ever been grown, is the one process that has unfaiHngly 

 resulted in the production of healthy offspring. This requires a rigid 

 selection. No corms should be planted which show any signs whatsoever 

 of disease after the husks are removed. Care should be exercised during 

 the growing season to see that no infested soil nor diseased plant parts 

 are carried to the soil in which the healthv corms are growing. 



