S<?pteinlier 4. li'L'O 



HO RT 1 (V LT URE 



187 



CARNATION STEM ROT 

 From the data and exi)erinR'nlal 

 evidence at the Illinois Kxperinienl 

 Station it seems clear that th.' con- 

 trol of stem rot (Rhizoctonia Solani) 

 of carnations lies along the line of 

 careful control of g^rowing conditions 

 of the carnation plant and in the use 

 of a clean soil. The disease is a soil 

 disease. The organism lives in the 

 soil, under ordinary conditions, as a 

 saprophyte, but under more favorable 

 conditions attacking the carnation 

 plant and causing its destruction. The 

 conditions influencing its si)read and 

 development are high soil temiiera- 

 lure and soil moisture. 



Soil Disinfectants of Little Value 



The results of these experiments 

 indicate that the usual soil disinfec- 

 tants, such as suli)huric acid, lime, 

 Mordeaux. copper sulphate and for- 

 malin, applied to the soil have but 

 little effect on the fungus and that 

 they are consequently of little value 

 as a means of controlling the disease. 

 Xo chemical solution was found 

 which, when applied to the soil in 

 quantities not harmful to the plant, 

 eradicated the fungus. The fungus is 

 very resistant in soil to weak solu- 

 tions of acids and alkalies. It is also 

 resistant to low temperatures and dry- 

 ing. Evidence is presented that it 

 lives in soils for years, resisting all 

 the rigorous conditions of a cold win- 

 ter and a hot summer. 



Steam Sterilization Effective 



In order completely to eradicate 

 the fungus from the soil, steam ster- 

 ilization alone seems to be effective. 

 I>ry steam forced through the soil at 

 forty pounds pressure for one hour 

 will destroy the fungus. There is no 

 indication that such sterilization of 

 soil is accompanied by evil effects on 

 the growth or the production of car- 

 nation plants. Sterilized soil Rrows 

 equally good carnation plants as un- 

 sterilized soil. However, aside from 

 the labor and expense Involved in 

 sterilization, unless the plants brought 

 in from the field are free from th<^ dis- 

 ease organism the disease may again 

 be introduced into the soil of the 

 benches. There is. of course, but 

 little assurance that the fungus is not 

 present in the field. In order to pre- 

 vent the introduction of the disease 

 from the field into the benches, only 



healthy and uninjured plants should 



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be used. Every plant should be care- 

 fully examined at the crown for evi- 

 dences of the disease and any plant 

 showing symptoms should be dis- 

 carded. 



Temperature and Moisture 



The first month the plant is in the 

 bench is the most critical point in the 

 lite of the plant, especially if the 

 transplanting is done early. The tem- 

 perature of the greenhouse is high at 

 this time, and still more important, 

 owing to the large amount and the 

 frequent use of water concomitant 

 with transplanting, the humidity of 

 both soil and air is high. Experi- 

 ments have shown that high tempera- 

 ture and high water content of soil, 

 especial)" .vhen existing simultane- 

 ously, off-,T a most favorable environ- 

 ment to the fungus. High tempera- 

 tures in the cutting bench and in the 

 carnation house give Rhizoctonia a 

 two-fold advantage; they lower the 

 vitality of the cuttings and plants and 

 give the fungus optimum conditions 

 under which to develop. In other 

 words, when normal temperature for 

 the best development of the plant is 

 furnished, no stem rot occurs; while 

 if high temperatures are maintained, 

 the vitality of the plant is lowered, 

 thus making it more susceptible to 

 stem rot. At the same time, high 

 temperatures favor the growth of the 

 fungus, increasing its virulence. A 



careful watch, therefore, ot the grow- 

 ing conditions of the plants is neces- 

 sary at this time. The temperature 

 should be kept as low as possible and 

 no more water applied to the soil than 

 is absolutely necessary for a healthy 

 growth of the plant. 



These statements apply also to the 

 growing of seedlings and cuttings. 

 Steam sterilization of soil and sand is 

 recommended whenever it is possible. 

 The cutting bench offers a most fa- 

 vorable environment for the growth 

 of the fungus if it is present in the 

 sand. A relatively high temperature 

 and high percentage of moisture of 

 the sand, as well as the high hu- 

 midity of the air resulting from arti- 

 ficial shading, are characteristic of 

 the cutting bench. Under such condi- 

 tions it is extremely difficult to con- 

 trol damping-off if it is present in the 

 sand. It is therefore recommended 

 that the sand be sterilized with steam 

 and careful attention given later to 

 the moisture and temperature condi- 

 tions. A relatively high temperature 

 of soil together with a high percent- 

 age ot moisture is conducive to infec- 

 tion. It is important, therefore, that 

 the temperature be kept as low as pos- 

 sible for a good healthy growth of the 

 carnation plant. This temperature, 

 since it is lower than that of the 

 optimum temperature ot the fungus, 

 will prove an important factor in the 

 control of infection. 



