26 



The Weekly Florists' Review. 



MabCh 14. 1912. 



STEM-ROT STUDIES AT URBANA. 



[A paper by W. H. AuUersoii. assistant lu florl- 

 cultural pathology at the Illinois Kxperiment 

 Station, read before the Illinois State Florists' 

 Association at Joliet March C] 



In undertaking an investigation of 

 the diseases of floricultural plants the 

 writer was of the opinion that a thor- 

 ough and complete study of a single dis- 

 ease was preferable to a more or less 

 superficial study of a larger number of 

 the many diseases affecting our floricul- 

 tural crops. After consulting with a 

 number of prominent florists of the 

 state, it was decided that the disease 

 known as soft or wet stem-rot of car- 

 nations was of the greatest economical 

 importance to greenhouse men, since 

 the fungus causing this disease is also 

 known to cause a number of other dis- 

 eases of greenhouse crops. 



The literature on this disease is ex- 

 tensive, but no thorough investigation 

 has ever been carried out, so that a 

 certain amount of preliminary work had 

 to be undertaken in order to confirm 

 such inyestigations as had already been 

 made. These preliminary investiga- 

 tions have occupied the time of the 

 writer since July and a few of the 

 results obtained will be given in this 

 report, although a number of experi- 

 ments which have been started are not 

 completed as yet, and therefore will not 

 be mentioned here. 



Two Kinds of Stem-Rot. 



There are two recognized stem-rots 

 ot carnation, which should not be con- 

 fused. One, called the dry stem-rot, is 

 believed to be caused by a fungus of 

 the genus Fusarium. This same fungus, 

 but perhaps another species, causes the 

 drying of the lower leaves of the car- 

 nation plant so often noticed in the 

 benches. So far as I have observed, 

 this disease is not of any great eco- 

 nomical importance, since only the older 

 leaves are attacked. But the fungus 

 mentioned above as causing the dry 

 stem-rot seems to work in the interior 

 of the stem and to cause the death of 

 the larger branches and often of the 

 main stem. The stem and branches 

 when attacked by this fungus grad- 

 ually wilt and the leaves turn to a 

 yellowish brown or about the same color 

 as the leaves dying at the base of a 

 . normal plant. This yellowing or dying 

 of the branch is rather rapid compared 

 with the other stem-rot. In the dry 

 stem-rot the stem remains firm after 

 death, although wilted and shriveled, 

 and if pressed with the fingers the bark 

 does not slough off, while the fibers of 

 the stem beneath the bark remain in- 

 tact as in a dried or normally wilted 

 stem. The contrast to that of the wet 

 stem-rot is marked. 



The wet stem-rot, which has caused 

 the carnation grower of this country so 

 much trouble and which has so often 

 been called the most serious disease of 

 carnations, is caused by a fungus called 

 Ehizoctonia. It is hardly necessary 



to describe the symptoms of this disease 

 to a convention of florists, since they 

 are all only too well acquainted with it. 

 The fungus usually attacks the plant 

 at its crown; that is, where the stem 

 enters the ground. It may enter at this 

 point or lower and growing up one side 

 of the stem may cause the death of only 

 a single branch. This is often the case 

 where the plants are set rather low in 

 the soil; for example, when they are 

 finally brought from the field into the 

 house in the fall. Usually the first in- 

 dication of the disease is a paler green 

 color of the entire plant or of a single 

 branch. The plant does not wilt at 

 once, for the pale bluish green color 

 of the foliage may be noticed for a 

 week or so before any actual wilting 

 takes place. If one presses the stem 

 of such a plant just above the soil be- 

 tween the thumb and forefinger a soft 

 area is usually felt and a slight twist 

 is suflicient to slough off the bark, be- 

 neath which is usually a slimy wet 

 area which gives this rot its character- 

 istic name. Often, however, the stem 

 is dry at the point of attack and upon 

 breaking off the stem at this point the 

 fibers of the stem are seen to be sep- 

 arated, giving a brush-like appearance 

 to the broken stem in contrast to the 

 firm stem of the dry rot. 



Attempt to Determine Extent. 



In order to obtain some definite in- 

 formation as to the extent of this lat- 

 ter disease in the state and also to get 

 good material for our studies of the 

 fungus itself, we sent letters to about 

 eighty growers of the state, requesting 

 information and material. The response 

 to this appeal was somewhat disappoint- 

 ing, for from these eighty letters we 

 received ten replies and with the ten 

 answers we received six packages of 

 specimens. In four packages were stem- 

 rotted plants; in two, carnations suffer- 

 ing from other diseases. Since we have 

 seldom visited a carnation greenhouse 

 without finding some stem-rotted plants, 

 we believe the lack of material could 

 not have accounted for the above facts. 

 Such material and replies as we have 

 received, however, seem to indicate 

 that this disease is fairly well distrib- 

 uted over the state and we know from 

 other publications that it is found in 

 most carnation beds throughout the 

 United States. 



In making an investigation of this 

 disease it was thought best to study the' 

 fungus causing the disease and to learn 

 something of its methods of attack 

 before making any suggestions concern- 

 ing possible methods of control, for only 

 too often superficial studies lead to 

 recommendations to growers which are 

 not only impracticable but are often 

 harmful. No suggestions concerning the 

 control of this disease will be made by 

 us in this report, aside from merely 

 sanitary precautions which every care- 

 ful grower should observe. 



Fungus is in the Soil. 



The organism which causes this dis- 



ease is a fungus. Fungi are plants, just 

 as the carnation is a plant, but they 

 are lower forms of plant life. We are 

 all familiar with the rusts, the mildews 

 and molds, all of which are fungi. 

 This particular fungus lives in the soil 

 and may thus live for years without 

 causing any trouble. It is very abun- 

 dant in the soil and undoubtedly is 

 present in most greenhouse bench soils. 

 The question naturally arises: If this 

 fungus is so universally present how 

 can we raise any plants at all, since 

 it surrounds all the plants in the bench t 

 There are a. number of factors involved 

 in the answer to this question and our 

 experiments are not yet completed 

 along this line. 



An experiment to prove that this 

 fungus was the real cause of the disease 

 was undertaken. This experiment 

 showed that when the stem below the 

 soil is injured so as to expose a por- 

 tion of the stem beneath the bark and 

 the fungus placed in contact with this 

 exposed area, then the plants always 

 die from the typical stem-rot disease. 

 On the other hand, if plants are so in- 

 jured and no fungus is added to the soil 

 the wound heals over and in a few 

 weeks only a callus can be seen at 

 this point. If the fungus was put in 

 direct contact with a healthy, unin- 

 jured stem it was found that about 

 seventy-five per cent of the plants died 

 from typical stem-rot, while only twen- 

 ty-five per cent remained healthy. But 

 in this case the fungus was very much 

 longer in attacking the stem than when 

 it was injured. 



These plants were old plants and in 

 vigorous condition, but the soil was 

 kept a little damper than in the benches 

 under ordinary cultural conditions. In 

 the few cases where we have merely 

 placed the fungus in the neighborhood 

 of the plant, but not in actual contact 

 with the stem, we have found infection 

 takes place only rarely. Thus it is evi- 

 dent that in the case of plants brought 

 from the field into the greenhouse bench 

 any injury to the stem, a bruise or 

 cut, makes this plant all the more easily 

 attacked by this fungus. We believe 

 that this partly accounts for the rather 

 heavy loss from stem-rot which is usual- 

 ly experienced for a few weeks in the 

 fall when the plants are i)rought into 

 the house. Other factors, such as shade 

 and damp soil, both favorable for a 

 rapid and vigorous growth of the fun- 

 gus, have their influence also during 

 this period. 



Rotted Plants Good Pastures. 



Our experiments further show that 

 when a plant suffers from stem-rot it 

 is an indication that the fungus is 

 abundant in that neighborhood. Fur- 

 ther, a rotted plant is a good pasture 

 for the fungus, upon which it can gain 

 renewed energy and from which it 

 grows out into the surrounding soil in 

 greater abundance and renewed vigor. 

 For this reason plants attacked by the 

 stem-rot fungus should be immediately 

 dug up, the soil in the area up to the 

 neighboring plants should be carefully 

 removed and taken entirely out of the 

 house. Very often several plants adja- 

 cent in the bench are seen to follow 

 a single stem-rotted plant. This may 

 often be prevented by the above treat- 

 ment. Further, moisture is necessary 

 for a rapid spread of this fungus. In 

 the drip of an angle in one of the sta- 

 tion greenhouses four plants were seen 



