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Greenhouse - Lilac

( Originally Published 1920 )

Cultural Considerations. Indoor lilacs at first require a cool house. The temperature is gradually increased to about 60 degrees. The plants require frequent syringing and moderate ventilation.


Forced lilacs are subject to a few diseases. The plant is generally considered very hardy.


Caused by Pseudomonas syringe van. Hall.

Symptoms. The disease as described by Gussow seems to be confined to the leaves. The writer has found a blossom blight of the lilac both indoors and in the field. In pure culture, the organism resembled P. syringe. The affected leaves become greatly disfigured; the disease spreads very rapidly.

Control. It is doubtful whether spraying will be of any avail. The plants should be given plenty of ventilation whenever possible. Diseased leaves should be destroyed by fire. As far as possible the leaves of the plants should be kept dry; all the water should be applied with the hose on the ground, a method that also avoids the splashing of soil particles.


Caused by Phytophthora syringae Kleb.

This disease was found by Klebahn to be very serious in propagating beds in Germany. The causal organism attacks and kills the twigs at a distance of several internodes above ground. The flower buds from the affected shoots fail to develop altogether. However, new shoots may appear below the affected area. The disease is of no economic significance in the United States.


Caused by Microsphaera alni (Wal.) Salrn.

Symptoms. Powdery mildew is perhaps one of the commonest troubles of forced lilacs. The disease is characterized by white powdery patches on the surface of the leaves and stems of the plant. The causal fungus attacks a large number of outdoor plants besides the lilac, as chief of which Lonicera, Alnus, Betula, Quercus, Carya, Castanea, Juglans, and Platanus may be mentioned. Outdoor lilac often suffers greatly from this mildew.

The Organism. The perithecia are either scattered or crowded greatly, varying in size. This seems also true for the appendages, which vary in length and in numbers, but are rigid, and colorless throughout, excepting the amber brown base, and dichotomously branched at the tips, the latter branches being regularly recurved. The asci are short stalked, ovate to globose; the ascospores are 8 in number.

Control. This mildew may be controlled in the same way as the rose mildew (see p. 323).

LILIES (Lilium longiflorum)

Cultural Considerations. The secret of success with lilies is in strong and vigorous bulbs. Lilies forced for the Christmas market should be planted in a rich soil thoroughly mixed with well rotted stable manure. After having been potted, the bulbs should be placed in a cold frame or in a cool dark cellar to encourage the rapid rooting. After that they are maintained at a temperature of 5o, then 6o, then 75 degrees F. in the house. Lilies for the Easter trade are bought about the middle of December. Lilium speciosum var. rubrum is especially well adapted for forcing.


Lilies are subject to quite a number of diseases all of which are of economic importance.


Cause, cultural and mites.

Symptoms. The trouble is characterized by a spotting and distortion of the leaves, flowers, and scales of the bulbs, as well as by a general stunting in growth. In severe cases, there appear yellowish white, longitudinal, sunken spots, and streaks on the first leaves as they show above ground. As growth proceeds each succeeding whorl becomes similarly affected, and finally collapses and dries. Even the flowers become spotted, shrunken, and distorted. Occasionally plants appear healthy, until the disease suddenly breaks out on the flowers. It is seldom that all the leaves in the same whorl are uniformly affected (fig. 58, b and c.). The diseased foliage or whorls may be irregularly scattered along the main stalk. The greatest damage occurs when the flowers are spotted, since the plants become un-salable whether the leaves are healthy or not.

Cause. There are many current theories as to the cause of the disease. Some growers believe that it is due to soil exhaustion. Others believe that it is due to the removal of the flower stalks by the growers in Bermuda, who desire to sell them, thus giving them a double source of profit. It is claimed that this practice weakens the bulbs by depriving them of their proper nourishment. Still others are of the opinion that the bulbs become weakened by being harvested prematurely. Finally some growers hold that the trouble is due to an insect which feeds on the scales of the bulbs. The investigations by Woods have shown that the trouble is brought about by a combination of causes. Poor cultural conditions such as overwatering, or the use of poor, unselected bulbs will generally and indirectly tend to cause this disease. The bulbs may be further weakened by the attacks of a mite (Rhizoglyphus echinops) and of certain fungi and bacteria. The bulbs may also become weakened by allowing the roots to dry and then overwater.

Control. The disease cannot be cured. The best that can be done is to select strong, healthy bulbs. Crop rotation to prevent the spread of the mite is also recommended.


Lilies are subject to several rust diseases. The most important is the American rust and is caused by a species of Uromyces. This disease according to Halsted was first found on leaves of Lilium candidum at Buffalo, N. Y.


Caused by Botrytis sp.

Symptoms. The trouble is apparent as small rusty spots upon the buds, leaves, and blossoms.

With the advance of the disease, the spots become coated with a fuzzy, brownish coat, made up of the fruiting stalks. As the plant becomes decayed, numerous sclerotia appear. The disease is spread in the hothouse through the watering or in syringing. Infection is favored by a high humidity and poor light conditions in the house. Little is known of the causal organism (fig. 58, d.).

Control. The disease may be kept in check by proper ventilation.

CALLA LILY (AraceŠ spp.)

Cultural Considerations. The yellow callas are grown in the same way as the white callas except that they seem to do better without a rest period. White callas require a rich soil, full sunlight and an abundance of water during the growing season. During the summer, the plants undergo a resting period. The pots are laid out in the open in the shade and a little water is given occasionally to pre-vent the Rhizomes from drying out.


Callas are apparently a hardy plant. It is subject to but few diseases.


Caused by Bacillus aroideŠ Town.

Symptoms. This disease may be found both on calla lilies in the greenhouse or, in the field. The callas usually rot off at or below the surface of the ground, the disease frequently spreading downward in the direction of the corms and upward into the leaves. Occasionally soft rot starts at the edges of the leaves or at the flower stalk. The disease spreads more rapidly and is also worse in greenhouses where callas are grown in solid beds.

In cutting open a diseased corm, one observes a line of demarkation between the healthy and diseased tissue, the latter being brown, soft, and water soaked. Affected leaves become slimy without necessarily losing their green color. If the disease at-tacks flower stalks, the flowers turn brown and the stalk falls over although its green color is preserved. As the disease progresses under ground the plant above ground topples over without any sign of disease. Under unfavorable conditions, the disease in the corm may not progress further than a small spot which soon dries. The causal organism, however, remains alive in these spots, but dormant until the time when conditions of moisture and temperature again become favorable. The nature of the soil determines to a large extent the severity of the rot. A soil rich in humus is most favorable for its spread.

The Organism. Bacillus aroideae is a short rod with rounded ends, single or in chains of two or four. Its growth is white on solid media. It produces no gas, and liquefies gelatin. Although apparently distinct from Bacillus caratovorus Jones, it is nevertheless capable of producing a soft dark colored rot in carrot, potato, turnip, radish, cabbage, cauliflower, tomato, and in the fruit of eggplant and cucumber.

Control. The disease may be prevented from getting a start by discarding diseased or spotted corms. Changing the soil every third or fourth year, or steam sterilizing it will prevent infection of the healthy corms. Starting the plants in pots instead of planting them directly in the beds is also recommended. In this way, all diseased plants will be discarded before being put finally in the bed.


Caused by Phyllosticta richardia Hals.

Symptoms. This disease is characterized by large, ashy spots on the leaves. Within these spots may be found minute, dark fruiting bodies (pycnidia). Very little is known of the causal organism. Blight may often be confused with a spotting due to sun-scald. In this case, however, the dead tissue is invaded with the fungus Pestalozzia richardi a Hals.


Caused by Cercospora richardiecola Atk.

Symptoms. This disease was first found by Professor Atkinson in Alabama in 1891. The spots are black with small white centers, and may be formed on all parts of the leaves.

The Organism. The conidia are hyaline, and from 4 to 10 septate. The conidiophores are borne in bundles and are brownish to reddish in color, finally becoming reddish brown with age.

Control. This disease may be kept in check by spraying with a standard fungicide.


Caused by Rhizopus pecans Mass.

Symptoms. This disease is characterized by a soft rot of lily bulbs, especially Lilium speciosum, and L. auratum. The malady was studied by Massee who found it on imported bulbs from Japan. The causal organism seems to be a wound parasite, that gains entrance to the roots through a wound. From the roots, it works its way up to the scales and causes them to rot. Diseased bulbs generally become covered by a white weft of mycelial growth which is soon followed by numerous clusters of sporophores bearing black globose sporangia.

The Organism. The mycelium is white, the sporophores forked or simple. Sporangia globose, blackish to deep brown, columella large. Spores striated, pale olive. Zygospores dark, and covered with spiny warts.

Control. Where the disease occurs once, the soil should not be used again unless it has been sterilized with steam or formaldehyde. Injured bulbs should not be planted. In shipping bulbs, care should be taken that they are not packed damp.


(Funkia Undulata. var. Variegata)

Caused by Colletotrichum omnivorum Hals.

Symptoms. This blight is severe on the broad and the narrow leaved varieties, and especially on Funkia undulata var. variegata. The disease appears as spots at about the middle of the leaf. The tissue in these soon drop out, leaving the veins which run lengthwise. Badly diseased foliage have a shredded appearance. The same disease also at-tacks Aspidistra lurida var variegata, a plant closely related to the Funkia. At present, little is known of the nature of the causal organism.

Control. Halsted. recommends spraying with Ammoniacal copper carbonate. Attention should be paid to securing resistant varieties.

LILY OF THE VALLEY (Convalaria majalis)

Cultural Considerations. This plant may be forced at any time of the year. Sand is the best soil in which to grow it. It is advisable to begin with a bottom heat of 50 degrees F. and quickly raise it to 85 degrees. The plants require an abundance of water during the forcing period.


Lily of the Valley is considered a hardy plant. They are however known to suffer from two diseases.


Caused by Botrytis paeoniae Oud.

This disease, which is usually common on peonies and on lilacs, also frequently attacks the lily of the valley. The causal organism often attacks the pips first; then works its way up to the stems. Infected pips become soft, then become covered with a grayish mold, and are later peppered with greenish-black, flat sclerotia.

Control. The disease is often introduced with infected pips which have been previously injured, or kept under poor storage conditions, especially under too high temperatures and moistures. Hence only healthy pips should be used. If the soil becomes infected with the causal organism, it should be steam sterilized, or treated with formaldehyde (see pp. 32-43) the former method being preferred.


Caused by Dendrophoma convallariae Can.

This leaf spot often destroys entire beds of plants. Little is known of the causal organism or of methods of control.


Caused by Septoria majalis Aderh.

This disease is characterized by a general spotting which is unevenly scattered over the leaves. The spots, however, are found mostly on old and faded leaves, hence the trouble is of no economic importance.

MIGNONETTE (Reseda odorata)

Cultural Considerations. The soil required for mignonette is about the same as for carnations. Raised benches are preferred rather than pots. An inch of well rotted stable manure is placed at the bottom, and four inches of the compost on top. Young seedlings require an abundance of ventilation. During bright weather temporary shading is necessary. Mignonette is very sensitive to overwatering. The watering should be done in the morning. If water remains on the foliage over night, the plants will become badly spotted. The temperature of the house in cloudy days should not run above 55 degrees F. and in bright days not higher than 65 degrees.


Mignonette is subject to but few diseases. The most important of these may be mentioned as follows :


Caused by Cystopus candida (Pers.) Roussel.

This disease is commonly met with out of doors on practically all cultivated cruciferous plants. In Europe, white rust seems to attack the mignonette, but there are no records of similar cases in the United States.


Caused by Cercospora resedŠ Fl.

Symptoms. The trouble becomes apparent as minute pale spots with yellowish to brownish borders. In spreading over the entire leaf, it takes on a reddish discoloration. Usually, the lower leaves are most affected. Little is now known of the causal organism.


Caused by Rhizoctonia sp.

Root rot of mignonette may be expected wherever the soil in the benches is infected with Rhizoctonia. The young plants usually damp off. Older ones rot at the base of the stem and at the roots. In either case, affected plants are dwarfed, and the leaves have a sickly yellow color. For a description of the organism and for methods of control, see p. 20.

NARCISSUS (Narcissus bulbocodium)

Cultural Considerations. Narcissus is easily forced. After potting, a thorough watering should be given, as the bulbs fail to set roots in a dry soil. The pots should be placed in a cool cellar to en-courage root formation and to retard top growth. After bringing the pots into the greenhouse, they should at first be placed under the benches or under subdued light, and in a low temperature of about 50 degrees F. Later the plants are gradually exposed to more light. The more slowly they are forced the better the quality of the flowers. During the blossoming period great care should be given to the watering. At no time should the root system be permitted to become dry. On bright days the tops of the plants should be syringed until the flowers begin to show color.


Narcissus under normal care is very hardy and subject to very few diseases.


Caused by Puccinia schraeteri Pass.

This rust often attacks Narcissus poeticus. It is of no economic importance in the United States.


Caused by Fusarium bulbigenum Mass.

Symptoms. This trouble, which was studied by Massee, is said to be prevalent in England. Its presence in the United States has not been reported. The trouble first appears on the leaves as small yellowish spots. These, however, enlarge and work downward into the bulb scales, the latter of which soon rot. The disease is spread by partly diseased bulbs and through infected soil. Little is now known of the causal organism.

Control. Care should be taken to prevent the introduction of this disease into this country. All bulbs which show the least discoloration should not be used for planting.

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