Januabt 29, 1920 



The Florists^ Review 



25 



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CONTROL OF CARNATION STEM-ROT 



|T IS definitely known that 

 the cause of carnation 

 stem-rot is a fungus. This 

 fungus has been isolated 

 many times, identified and 

 studied in pure culture. The 

 important fact for our dis- 

 cussion at present is that this fungus 

 lives normally in the soil. So far as is 

 known, practically all tillable soils 

 harbor the fungus. It has been found 

 in practically every state of the Union 

 and in widely different types of soils. 

 It is probable that every greenhouse 

 contains it. In the soil it may live 

 either on dead organic matter or on 

 weeds and other plants. This is an 

 important fact regarding the habits of 

 the causal fungus. It seems to live in 

 the soil as a saprophyte; that is, it 

 gets its nourishment from lifeless or- 

 ganic materials, such as dead roots and 

 other parts of plants, but when the 

 opportunity of a favorable 



host and a favorable en- 



vironment is present it be- 

 comes a parasite. As a 

 parasite, it seems to be able 

 to attack and live on nearly 

 any form of plant. 



Extracts from a paper by Dr. P. A. Iiehen- 

 bauer, of the UniTerslty of Illinois, read at 

 the Chicago convention of the American Carna- 

 tion Society, January 21, 1920. 



ments have been conducted along this 

 line. Several investigators have rec- 

 ommended the application of formalin 

 to soil in order to control certain dis- 

 eases. Others have recommended lime. 



Sterilizing the Soil. 



A great variety of substances have 

 been tested, both in the field and in 

 greenhouses, such as iron sulphate, creo- 

 sote, carbolic acid, naphthalene and 

 bleaching powder, in order to rid soils 

 of certain fungi. On the whole, the re- 

 ports are contradictory and inconclu- 

 sive. At the Illinois experiment station 

 extensive tests were made with sul- 

 phuric acid, lime, Bordeaux mixture, 

 copper sulphate and formalin, but none 



Point of Attack. 



Another important fact 

 in the life history of the 

 fungus is that it does not 

 attack the leaves or upper 

 portions of the plant, but 

 enters the plant at the 

 crown; that is, it attacks 

 the stem at a point just 

 below or just above the sur- 

 face of the soil. This fact, 

 together with the fact al- 

 ready mentioned, that the 

 fungus is' found in prac- 

 tically all soils, must be 

 kept in mind in any attempt 

 to control the disease. 



In attempting to control 

 a plant disease, such as car- 

 nation stem-rot, one of sev- 

 eral methods naturally is 

 thought of. One is to spray 

 the plants with some poisonous material 

 which will either destroy the fungus or 

 leave a deposit of this poison, so that 

 when the fungus spore begins to ger- 

 minate it will soon be killed. This 

 method is used often and proves suc- 

 cessful in the case of many diseases. 

 But spraying is not eflBcient in the case 

 of carnation stem-rot. This is because 

 the fungus does not make its growth 

 on the leaves. It does not produce 

 spores which drift about in the air, 

 fall upon the leaves, germinate and 

 grow, as is true of many other diseases. 

 The fungus lives in the soil and attacks 

 only the plant stem at its base, near 

 the surface of the soil. Spraying the 

 tops of the plants, therefore, is use- 

 less. 



The second method of control which 

 suggests itself is to treat the soil. 

 Since the organism lives in the soil, it 

 is but natural to suppose that, if we 

 can find some disinfectant which when 

 applied to soil will destroy the parasite, 

 the problem is solved. Many experi- 



"Dr. Lehenbauer*s paper," said 

 W. N. Rudd, chairman of the A. C. 

 S. committee to review it, "was the 

 best by a scientific man 1 have ever 

 listened to. It concerns a subject in 

 which we are all interested and it is 

 w^ritten in language that w^e can all 

 of us understand;** 



plant artificially inoculated at the base 

 of the stem, I have found, may live for 

 a month and not show any effects, and 

 then quickly begin to wilt and die. 

 Plants brought from the field may ap- 

 pear healthy, but when set into the 

 bench of sterile soil, die after a short 

 time from stem-rot. It is quite possible 

 that such plants were infected while 

 growing in the field. 



Sterilizing the soil, therefore, is not 

 entirely a successful method of control. 

 The third method of attack of the 

 problem of control appears somewhat 

 more promising. It lies in the regula- 

 tion of the environmental conditions in 

 such a way that the host is kept at its 

 optimum vigor while the activity of the 

 parasite is reduced. In other words, it 

 consists in regulating the temperature, 

 moisture and air in such a way that 

 either the plant is strong enough to re- 

 sist the fungus or the fungus is not 

 strong enough to attack the 

 plant. By the practical 

 grower environmental condi- 

 tions are usually considered 

 all-important. 



Temperature of Soil. 



of these substances proved efficient in 

 controlling carnation stem-rot. 



Sterilizing the soil by means of steam 

 is recommended often and this method 

 is efficient in the case of certain dis- 

 eases. There is no question that the 

 stem-rot organism can be destroyed in 

 soil by means of steam sterilization. 

 But it is questionable whether we can 

 control the disease in our greenhouses 

 by this method. It may be possible to 

 sterilize all the soil before the benches 

 are filled and planted to carnations. 

 However, the soil- of the field contains 

 the fungus and when we set the plants 

 into the benches some soil necessarily 

 must adhere to the roots of the plants. 

 The soil on the roots, be it only a small 

 quantity, may contain the fungus and 

 this small quantity of soil on the roots, 

 therefore, will reinoculate the sterile 

 soil in our benches. There is still an- 

 other fact we must keep in mind. The 

 fungus may penetrate the stem of the 

 plant while the latter is still in the field. 

 For a time this is not noticeable. A 



That there is an actual 

 correlation between cli- 

 matic conditions and plant 

 diseases is obvious to most 

 of us. The practical plant 

 grower has always been in- 

 clined to blame the weather 

 for his mildews and his 

 rusts. The scientific plant 

 pathologiflt, on the other 

 hand, has been in the habit 

 of giving the influence of 

 the weather only a passing 

 interest; he has been de- 

 voting most of his energy 

 to the study of the causal 

 organism. A study of both 

 is essential if we are to b© 

 successful in the control of 

 diseases. 



Various experiments in 

 the treatment of outdoor 

 crops have proved that there is a defi- 

 nite relation between soil temperature 

 and the prevalence of disease. A cer- 

 tain maximum range of soil tempera- 

 ture seems to be necessary; when the 

 temperature is above this range, the 

 parasite becomes destructive; when be- 

 low, it loses its power and lives only 

 as a harmless saprophyte. 



As has just been stated, that conclu- 

 sion was reached by means of experi- 

 ments with diseases of field crops. In 

 the field, of course, the soil temperature 

 is not under our control. In the case of 

 the carnation, which is grown, for the 

 greater part of the time at any rate, 

 in the greenhouse, does the same rela- 

 tion hold between soil temperature and 

 the prevalence of stem-rotf At the 

 Illinois station we followed up the rela- 

 tion of environmental factors to stem- 

 rot and we also came to the conclusion 

 that temperature ia the important fac- 

 tor in the prevalence of this disease. 

 We found that the stem-rot organism 



[Continued on page 77.1 



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