60 MASS. EXPERIMENT STATION BULLETIN 427 



All-year culture in the greenhouse is an effective method of controlling Alter- 

 naria blight. Fielding the plants increases the hazards from disease. The preva- 

 lence of disease increases as transplanting into the greenhouse from the field is 

 delayed beyond the first week in July. 



Care in lifting and transplanting to avoid breakage is an important disease 

 control measure. The oldest or earliest-propagated stock is most easily injured 

 and generally less tolerant of changing and unfavorable growing conditions, 

 and more subject to wilt diseases. For disease-susceptible varieties, delaying 

 propagation until January might be advantageous in some years. 



Infection and the advance of wilt diseases are favored by excessive watering, 

 overhead watering, warm greenhouse temperatures, and stagnant, moist atmos- 

 phere. Such extreme conditions are likely to exist from July to September. 



Setting the plants deeper than the roots at any of the stages of culture encour- 

 ages infection notably by the Rhizoctonia stem rot fungus. 



Fumigation of carnations with naphthalene base materials for controlling in- 

 festations of the red spider mite represents a notable improvement over the 

 former practice of syringing the plants with strong sprays of water. The change 

 has contributed to better disease control and to an improvement in the quality 

 of the flowers. 



Diseased plant remains and plants wilting from disease are potential sources 

 of inoculum and should be disposed of in a sanitary manner. 



The young plants and flowering stock require distinct care. The spread and 

 continuity of disease may be controlled by a careful supervision of the young 

 plants. Entire flats of young plants or classes of stock should be discarded in 

 the event of a progressive loss from disease among them. Segregation of the 

 two classes of stock is desirable, and a house devoted wholly to young plants is 

 recommended. 



Distinct contrasts in the susceptibility of carnation varieties to AUernaria 

 diatithi and Fusarium dianthi are shown. The pedigree of several varieties has 

 been traced in an effort to find the source of resistance and susceptibility to AUer- 

 naria dianthi. The culture of varieties resistant to disease is recommended where 

 a serious disease problem persists. 



The subject of soil sterilization with heat and chemicals in relation to disease 

 and weed control is reviewed. The effect of treating new and used soil in the 

 benches with chlorpicrin was not significant when the plants were grown in the 

 field in apparently infested soil. The sterilization of the potcing and flatting 

 soil by an}' acceptable method is very desirable. 



Powdered naphthalene, copper compounds, and calcium arsenate are lethal to 

 the conidia of AUernaria dianthi. Lead arsenate, lime, and sulfur materials are 

 not toxic. The toxicity of several chemicals to the spores was determined by 

 different techniques. 



Good control of Alternaria blight was shown in small-scale tests with Bordeaux 

 combined with calcium arsenate and fish oil, and with dusting mixtures con- 

 taining naphthalene, calcium arsenate, monohydrated copper sulfate, and lime. 

 In epidemic years significant control of blight in the field was shown by protective 

 treatments with Bordeaux mixture 4-4-50 combined with calcium arsenate 1 

 pound and Penetrol 3^ pint. Increases in yields of flowers are shown. Calcium 

 arsenate alone was injurious. Dusting materials gave unsatisfactory control. 

 Satisfactory results from spraying require frequent treatments with a power 

 sprayer beginning after the plants are fielded in May and continuing to benching 

 time in the greenhouse, or early July. Spraying treatments are desirable for 

 susceptible varieties, but only where field culture is practiced. 



