.Mat 12, 191>1 



The Florists^ Review 



23 



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OLD WILT IN NEW 



NEW DISEASE ON SNAPDRAGONS. 



By JOHN C RASMUSSEN. 



An Old Wilt in a New Place. 



A new disease of snapdragons has ap- 

 peared in Indiana. Perhaps it is some- 

 what erroneous to say ' ' a new disease, ' ' 

 because it is really an old enemy, espe- 

 cially familiar to lettuce and cucumber 

 growers. However, it has not been re- 

 ported on antirrhinum previous to this 

 time. 



The name of the fungus, to those scien- 

 tifically inclined, is Sclerotinia liber- 

 tiana. It is better known to greenhouse 

 men, especially vegetable growers, under 

 the names of lettuce wilt, lettuce drop, 

 cucumber wilt and timber rot. A wilt of 

 petunias and of numerous unimportant 

 plants is also ascribed to this fungus. 



The virulence of attack on lettuce 

 plants, both indoors and in the field, is 

 such that as much as from fifty to seven- 

 ty-five per cent of the crop has been lost. 

 Likewise, a few years back, cucumber 

 growers faced similar losses due to this 

 fungus. How badly the antirrhinum, 

 with its harder wood, may be affected is 

 a question answered by only one case. 

 At Anders Basmussen's place, at New 

 Albany, Ind., where this infestation first 

 made itself noticeable, the head foreman 

 estimates the season's loss of plants at 

 100, or eight per cent of the total num- 

 ber of plants. The disease made its ap- 

 pearance in the dull winter months. The 

 vigorous spring growth has not seemed 

 to abate the slow, steady attack to any 

 marked degree. At Christmas there were 



Infected' Snapdragon Plant. 



I Mycelium Appears on St«'in aiut at Base.) 



about ten or twelve diseased plants in 

 the bench. At Easter there was a like 

 number. The disease was not confined to 

 one particular spot in the benches, al- 

 though at one place there were six dying 

 or dead plants. The fact that this dis- 

 ease was spread over a 300-foot bench 

 seems to indicate that it was brought in 

 either in the soil or the manure. 



How It Acts. 



The first indication of trouble is a 

 wilting of the plant or of a part of the 

 plant. In many instances one branch 

 will wilt, followed in a few days by wilt- 

 ing of the whole plant, succeeded by 

 death. The infected branches, or the 

 main stem, or both, turn brown. If the 

 grower looks closely he will usually see a 

 white cotton-like material clinging to the 

 brown, dead stem tissue. This is the 

 mycelium, or vegetable portion of the 

 •fungus, which has entirely permeated 

 the stem and has finally burst through 

 the bark. This cottony growth is not al- 

 ways visible when the plant dies. How- 

 ever, it appears if the plant is allowed 

 to remain in the bench for several days 

 after death. One of the illustrations 

 shows a plant which was artificially in- 

 oculated with the disease, from pure 

 culture. The fine, thread-like mycelium 

 can plainly be seen at the base of the 

 plant and on the stem. The wad of cot- 

 ton, which was used to hold down evap- 

 oration and keep in moisture at the base 

 of the plant, is also visible on the soil. 



If the plant is undisturbed, small, 

 hard, black bodies of irregular and vary- 

 ing shape develop, ranging from the size 

 of a shot to the size of a pea. These 

 bodies are called sclerotia. They develop 

 both on the outside and in the interior 

 of the diseased stems. The larger num- 

 ber of these sclerotia will be found in the 

 pithy, brown stem by carefully splitting 

 the branch. One of the photographs 

 shows vertical sections of diseased stems 

 containing these bodies. 



Determining the Disease. 



The significance of emphasizing these 

 sclerotia is twofold. One is that they 

 are a clinching means of identifying this 

 disease; the other lies in the fact that 

 herein is the weak point in the life cycle 

 of this fungus, which allows us good 

 control. 



The methods of control are those of 

 prevention. There is no known cure for 

 a fungus-permeated plant. These sclero- 

 tia, alone, are capable of carrying this 

 disease oyer from one year to the next. 

 They may live over more than one year, 

 but in such reduced numbers as to be of 

 little consequence. Therefore, get rid of 

 the sclerotia formed this year, by de- 

 stroying every plant that has the infec- 

 tion, as shown by the obvious wilting of 

 the plant. Dr. F. L. Stevens demon- 

 strated the efliciency of this method in 

 1906, in North Carolina, when growers 

 of frame lettuce were suff^ing enormous 

 losses. 



Beds of lettuce, containing about 

 1,200 plants in all, were inoculated with 

 this disease. All of the plants died. 



Next year, in the same bed without fur- 

 ther treatment, 545 plants out of 1,200 

 died. This time, each plant was removed 

 and destroyed as it died, thus preventing 

 any new sclerotia being left in the soil. 

 The following year in the same bed 

 only seven plants died. The next year 

 nine plants died. The control was prac- 

 tically perfect. Therefore, destroy your 

 sick plants as soon as you sec them. 



Spreading the Spores. 



The sclerotia do not directly cause in- 

 fection. They must first grow and produce 

 spores; a single one is estimated to pro- 

 duce approximately 300,000,000 spores, 

 or seeds as it were. These are spread 

 about by the various agencies of air cur- 

 rents and water, as in spraying. The 

 spores will not infect a plant directly. 

 They must first fall on some decaying 

 matter, as dead leaves or manure, and 

 get a good start there. The disease then 

 spreads to the plant. Here is a second 

 weak point. If the bench is kept clean 

 of decaying matter, there will be no suit- 

 able resting place for the fungus to get 

 started. 



Soil sterilization will kill all sclerotia 

 and hence limit the disease. 



The only thing that can be ;said about 

 possible infection from fresh soil is to 

 avoid soils on which there is known to 

 have been a wilt. 



In order to be sure that tho disease 

 which I have described wa.s due to the 

 fungus mentioned, I attempted to re- 

 produce the diseased condition on 

 healthy plants. I grew some of the cot- 



Vertical Section of Snapdragon Stem. 



(Arrows Indicate ScleroUa.^ 



