CARNATION WILT DISEASES 59 



SUMMARY 



The important fungous diseases of carnations in Massachusetts are spot, 

 blight, and canker caused by Alternaria dianthi Stev. and Hall; root, crown, or 

 foot rot caused by Fusarium culmorum (C. W. Smith) Sacc, F. avenaceum (Fr.) 

 Sacc, and other species of Fusarium; Fusarium branch rot or wilt caused bj- 

 Fusarium dianthi Prill. & Delacr.; and stem rot caused by Rhizoctonia solani 

 Kiihn. Distinctive symptoms of disease are associated with each pathogene and 

 wilting is common to all of them. 



Infection of carnation plants by Alternaria dianthi readily occurs in a humid 

 atmosphere even in the absence of plant injuries. Injuries to the foliage by 

 drought, infestations of the red spider mite, and other causes contribute to infec- 

 tion in the field. 



Fusarium culmorum and related species infect the plants through injuries in 

 the roots, stems, and branches and through snags and adhering remnants of 

 stems and leaves. 



Plant injuries are required for infection by Fusarium dianthi, which attacks 

 the roots, stems and branches. 



Rhizoctonia infection is generally more successful through injuries; but in- 

 fection is readily obtained by mixing the fungus with the soil and providing warm, 

 moist conditions. 



All of these pathogenes attack cuttings in the sand and plants in the various 

 subsequent stages of culture. The cut surface at the base of the cutting is a 

 favored point of attack. The natural cracking or checking at the base of the 

 cutting offers a favorable point of infection especially by the various species of 

 Fusarium. 



The optimum temperatures for spore germination and growth of the patho- 

 genes are approximately 75° F. for Alternaria dianthi; 77°-80° for Fusarium 

 culmorum; 80° for Fusarium dianthi; and 86°-88° for Rhizoctonia solani. 



The incidence of disease in the cuttings and in the young stock subsequent 

 to rooting is intimately associated with either infection latent in the cutting or 

 superficial spore inoculum. Such contamination is derived from unhealthy 

 stock plants or from normal plants adjacent to unhealthy stock plants. The 

 transfer of Rhizoctonia is excluded from this concept. 



The use of new and clean sand after each crop of rooted cuttings is recom- 

 mended, and the potentialities of used sand for rooting further crops of cuttings 

 is indicated. 



The direction of the cut through the stem in the preparation of the cuttings 

 is not important in relation to rooting, but a smooth, clean cut leaving no loose 

 remnant of tissue is preferred in relation to disease control. The injured ends 

 of leaf stubs left after trimming the cuttings offer infection courts for Alternaria 

 blight under favorable conditions, but the hazard is usually negligible. 



Immersion of the cuttings for 15 minutes in a 1-1,000 solution of potassium 

 permanganate, Ji ounce to 2 gallons of water, encourages rooting and provides 

 some degree of disinfection of superficial inoculum conveyed by the cuttings to 

 the sand. 



Potassium permanganate was the most effective chemical considered in the 

 tests. The various hormone materials used in practice to improve rooting are 

 not fungicidal and no significant advantage was shown from treating the cuttings 

 with both a hormone material and potassium permanganate. Powdering the 

 base of the cuttings with a 10 percent Fermate or Arasan dust gave good control 

 of wilt caused by the fungus F. dianthi without harming root action. 



