48 MASS. EXPERIMENT STATION BULLETIN 427 



Rhizoctonia Stem Rot. 



No resistance to Rhizoctonia solani has been established. 



SOIL STERILIZATION 



As early as 1897 Sturgis (65) considered that the disinfestation of the soil 

 with heat contributed to the control of Fusarium branch rot of carnations, but 

 his results were negative in view of complications arising from infection inherent 

 in the cuttings. Ward (68) advised the sterilization of the sand in the propagating 

 house and the soil in the benches and the selection of a new field. Van der Bijl 

 (67) reported no beneficial effect from treating the soil with formaldehyde, and 

 did not consider soil sterilization practical under the method of culture peculiar 

 to South Africa. 



Peltier (53) reported that formaldehyde used as a soil disinfestant to control 

 Rhizoctonia stem rot was but a partial success, the losses varying from 24 to 53 

 percent. Steaming the bench soil controlled the disease when the soil was arti- 

 ficially infested, but no losses occurred in the uninoculated and unsterilized 

 sections. The production and quality of the flowers were not affected by heating 

 the soil, nor were they consistently improved. Weinard and Decker (69) found 

 that the loss of plants from Rhizoctonia stem rot in old soils averaged about 4 

 percent compared with about 3 percent in new soil. The loss of plants on new 

 steamed soil was about 6 percent; on new unsteamed soil about 5 percent. The 

 loss on soil cropped for two years and steamed was about the same as on the 

 same soil unsteamed, or about 6 percent. After 15 years of steaming, 2 percent 

 of the plants were lost compared with 9 percent on the unsteamed plots. It was 

 not surprising to them that steaming the bench soil did not eliminate the stem 

 rot disease since soil was brought from the field on the plants. However, their 

 work showed that soil treated with steam year after year could be kept in a 

 highly productive condition indefinitely and the yield and quality of the flowers 

 greatly improved. 



Wickens (78) considered steaming the soil not an adequate control measure 

 for Verticillium carnation wilt in England. Steamed soil sometimes showed 

 greater losses than unsteamed, since cuttings from apparently healthy plants 

 are frequently infected and give rise to diseased plants. Steam sterilization of 

 the soil has met with numerous failures in England (Brown 10). Soil steaming 

 in relation to the control of Verticillium wilt is often discredited from the frequent 

 failure of treated beds to remain free from disease for the complete period of the 

 crop or throughout the second year (White 76). Brown (9) considered heat 

 sterilization of the soil effective, and formaldehyde 1-50 the best chemical. 

 The beneficial effect measured by the survival of the plants was comparable to 

 that of replacing the top soil with clean soil. 



White (71) considered the development and extension of soil sterilization es- 

 sential to the control of Fusarium wilt diseases in carnation nurseries in England. 

 Dowson ( 4) contended that the control of Fusarium wilt is best accomplished 

 by soil steaming and the growing of healthy plants, although no supporting 

 experiments are shown. 



Bickerton (5) reported appreciable control of Fusarium branch rot from the 

 treatment of the field and bench soil with either chlorpicrin or formaldehyde or 

 from the treatment of the bench soil alone with chlorpicrin well in advance of 

 planting. The treatment of the bench soil with chlorpicrin gave a significant 

 increase in flower production even though the plants had previously been grown 

 in infested soil. The value of treating the old soil in lieu of changing was clearly 

 shown. 



