CARNATION WILT DISEASES 51 



Occurrences of carnation wilt diseases are intimately associated with high 

 temperatures, excessively wet soil, inadequate drainage, plant injuries, deep 

 planting, faulty propagation, and infected cuttings. For example, the culture 

 of carnations in raised beds, in contrast to ground beds, has resulted in much 

 better control of the wilt diseases. Soil contamination exists generally where 

 carnations are grown under glass, but it appears to become a factor in the occur- 

 rence of disease only when sound cultural and propagating methods are seriously 

 violated. 



CONTROL OF ALTERNARIA BLIGHT WITH FUNGICIDES 



In general, foliage diseases of economic plants due to Alternaria and closely 

 related pathogenic fungi have yielded to control from protective spraying with 

 copper fungicides. Woods (81, 82) and others (14, 62, 63), in the first published 

 accounts of the disease, suggested spraying the plants with soap and Bordeaux 

 mixture from the time they are fielded in the spring to the time they are well 

 established again in the benches. Over the years since 1927, the writer has 

 advocated spraying the fielded plants with Bordeaux mixture and spreader 

 (28, 29, 30, 31, 32, 33). This treatment was recommended on the basis of funda- 

 mental studies and control experiments in the field (Fig. 14) which are reported 

 here for the first time. In the interval, Bickerton (6), working on Long Island, 

 New York, demonstrated the v^alue of field spraying and showed both a signi- 

 ficant reduction in infection and a significant increase in production. Other 

 workers and growers, without showing detailed results in support of spraying, 

 have recommended it as a proper treatment for the control of blight. 



Toxicity of Chemicals to Conidia 



Conidia of the fungus, Alternaria dianthi were readily obtained from blighted 

 carnation leaves. Four techniques were followed in determining the toxic effect 

 of the chemicals used: (1) Dry spores were gathered from diseased leaves with a 

 camel's-hair brush and deposited upon the dry chemical residues on glass slides- 



(2) the spores were first deposited on glass slides and subsequently the fungicide 

 was atomized or dusted upon the spore-bearing surface and the spray allowed 

 to dry, before the slides were placed in a damp chamber for spore germination- 



(3) the spore-bearing slides were sprayed and immediately placed in moist dishes 

 and the moist film on the spore-bearing surface was maintained throughout the 

 incubating period; (4) the slides were first sprayed or dusted with chemicals 

 the sprayed slides were air-dried, and drops of water suspension of spores were 

 then applied to the dry residue. 



As may be observed from Table 17, the procedure used has a bearing on 

 the action of the chemical. The presence of water in some instances rendered 

 the chemical deposit soluble, thereby destroying the viability of the spores. 

 This is notably true of the treatments containing copper or calcium arsenate. 

 Spores deposited in the dry residue and in a moist atmosphere germinated; those 

 in the residue in water or in a moist film were killed. Sulfur dust was not fungi- 

 cidal, and liquid lime sulfur concentrate 1-40 was fungicidal onlv when the spores 

 were wetted by the spray, suggesting the limited value of lime sulfur as a dis- 

 infectant. When a water suspension of spores or dry spores were placed on the 

 dry residue of lime sulfur, spore germination was not destroyed, indicating that 

 the residue after spraying offers no protection against infection. The same might 

 be inferred from the results obtained with a 1-200 solution of potassium sulfide. 

 Lead arsenate was not toxic. Lime was not toxic. All of the dry dust mixtures 

 containing naphthalene were fungicidal under each of the four methods of test- 



