Greenhouse - Cyclamen
( Originally Published 1920 )
Cultural Considerations. Greenhouse men prefer to sow the cyclamen seed in September and not in spring. In March, the seedlings are transplanted from a two-inch to a four-inch pot and put in a cold frame until large enough to go to a six-inch pot. During the summer, plenty of ventilation and shading should be provided and the plants frequently syringed. In the fall, they are brought into the greenhouse (fig. 52) and some heat provided. The winter temperature should average 55 to 60 degrees F. until the period of blossoming is over. As the leaves turn yellow, the pots are placed in a cool house, water withheld and the period of rest induced. However, a little water is given from time to time to prevent the bulbs from shriveling.
DISEASES OF THE CYCLAMEN
Cyclamen are subject to but few serious diseases.
Caused by Thielavia basicola Zopf.
The disease was reported by Sorauer as being serious in Germany. The general symptoms are the same as for the violets. For a description of the causal organism and general methods of control, see P. 355.
Caused by Glomerella rufomaculans, var. cyclaminis Patt. and Ch.
Symptoms. The spots are circular, watersoaked, with sharply defined borders.
The Organism. The acervuli of the causal organ-ism are brownish, large, conidia straight to slightly curved. Setae are few, short and rigid. It is very probable that this conidial stage is the same as that described by Halsted as Colletotrichum cyclamenę Hals. The ascus stage was found by Patterson and Charles. The perithecia are dense, found in definite light colored round spots, brown membranaceous, subglobose with distinct opening. The asci are eight spored, the spores are hyaline, one celled, oblong to elliptic. The methods of control would be the same as for Colletotrichum cyclamenę.
Caused by Colletotrichum cyclamens Hals.
Symptoms. Anthracnose produces spots (fig. 52) on the leaves which may be mistaken for the spots caused by Phoma cyclamenę. Infection may occur at any part of the leaf and spread in all directions. Cyclamen leaves are especially receptive to infection because of the fact that water is able to lodge and remain a long time.
Caused by Phoma cyclamenę Hals.
Symptoms. The disease attacks leaves of all ages. The affected portions become darkened. Later the spots become dry and lighter in color, made up of a series of concentric rings of light and dark bands. The dead spots become brittle and drop out at the least touch, giving the appearance of a shot hole. This trouble is different from the leaf spot caused by the Septoria cyclaminis Dur. and M. The causal organisms of both of these leaf spots are little known.
Control. Removing the affected leaves and spraying with a standard fungicide will materially assist in keeping the disease in check.
DRACENAS (Dracena fragans)
Cultural Considerations. The cultural requirements of Dracena are the same as for Cordyline, see p. 247.
DISEASES OF DRACENAS
Dracenas are usually considered a hardy plant. However, they are subject to a few but serious diseases.
LEAF SPOT AND TIP BLIGHT
Caused by Physalospora dracenę Sheld.
The conidial stage as first mentioned by Halsted is a species of Gloeosporium. However, the ascus stage was found by Sheldon, who named it Physalospora dracenę. The disease is generally confined to the tip of the foliage (fig. 53, a.). The affected tissue becomes straw colored and shrunken. The disease may be controlled by spraying with a standard fungicide.
PHYLLOSTICTA LEAF SPOT
Caused by Phyllosticta maculicola Hals.
Dracenę, particularly the beautiful species Cordyline terminales, are often subject to a leaf spot which renders them worthless. The disease attacks plants of all ages and sizes.
Symptoms. The trouble is characterized by small, brown, somewhat angular spots on the leaves (fig. 53, b.). The tissue adjoining the spots becomes yellowish in color. Within these spots may be found minute black bodies (pycnidia) from which the spores, when ripe, ooze out as long colorless tendrils. Little is known of the organism. The disease may be controlled by spraying.
Caused by Phyllosticta dracęnae Griff, and Maubl.
Symptoms. This trouble is manifested as minute, irregular pale spots and bordered by a narrow, brown colored elevated band. The pycnidia are not always present on the spots until the leaves fall off. The spores ooze out as whitish tendrils. This form of spot was first described by Griffon and Maublanc on greenhouse dracenae in France. Its extent in the United States is as yet little known.
Caused by Vermicularia concentrica Sev.
The thicker-leaved sorts such as Dracena goldiena and the variegated D. Lindemi are often subject to a blotch disease. The trouble is characterized by large, brown blotches on the leaves. Very little is known of the causal organism. Spraying with Bordeaux or any other colorless fungicide may control the disease.
Cultural Considerations, see Tulips, p. 348.
DISEASES OF THE DAFFODIL
The Daffodil is a very hardy plant. It thrives equally as well in the greenhouse as it does out of doors.
Cause, improper cultural conditions.
Symptoms. Yellow stripe is a disease which is more commonly met with under field conditions, but also appears on daffodils under glass. The trouble in its early stage is perceptible as a slight discoloration, or a yellowing of the veins of the leaves. In an advanced stage, the leaves become streaked with parallel bands of yellow. In extreme cases, the leaves wither and the plants fail to set blossoms. The disease was studied by Darlington, who decided that the cause of it is not a parasitic organism, but that it is due to some un,. favorable cultural conditions that are as yet undetermined. No methods of control are known.
ERICA (Erica spp.)
Cultural Considerations. Ericas are low growing evergreen shrubs which lend themselves admirably to forcing on a commercial scale. Too much or too little water is injurious to the plant especially during the blooming period. The plants should never be allowed to wilt. The pots should be renovated every year individually and the proper amount of water given. The plants also need all the ventilation possible.
FUNGI ON THE ERICAS
Ericas are apparently very hardy plants. The only fungus known to cause a disease on greenhouse plants is Stemphylium ericoctonum Br. and De By. The other recorded fungi are as follows: Cystospora ericeti Sacc., Sporonema obturatum (Fr.) Sacc., Trichosporium fuliginosum Karst.
Cultural Considerations. Ferns are propagated by spores, or by division of the clumps. The spores are sown on garden loam over which half an inch of fine sphagnum has been placed. The spores are scattered evenly, and after being sprinkled with water are covered with a glass. In the division of the crowns, they should be planted and kept in a cool house or frame until they make a good start. Most greenhouse ferns thrive best in a temperature of 6o to 65 degrees F.
The following ferns are usually grown on a commercial scale : Adianthum cuneatum and A. gracillinum. Adianthum farleyense seems among the best for decorative purposes. Pteris serrulata is also extensively grown. In large conservatories the tree ferns, especially Alsophila australis, is very much in favor. Of the ferns propagated and sold for dwelling house purposes may be mentioned the sword fern, Nephrolepis exaltata. The latter can stand the atmosphere of a dry room better than any other fern.
DISEASES OF THE FERN
Ferns as a rule are hardy plants when they are given reasonable care. They are, however, attacked by a few diseases which are of economic importance.
Ornamental ferns grown in greenhouse or in bay windows are often troubled by a tip burn of the foliage. This is generally confined to the tender new growth. Affected leaflets become brown at the tip, giving the entire leaf an unsightly appearance. There may be various causes responsible for this trouble. An insufficient water supply at the roots will cause the tender leaflets to wilt. If the soil is allowed to remain dry for any length of time, the wilted parts will dry out and become brown. Poisonous gases either from smoke or fumigation will also cause the tender leaflets to dry up and die, thus giving them a burned appearance. Extremes of heat or cold will have a similar effect on the tender tips of the foliage.
Control. It is evident that in this case removing the cause of the trouble will effect a cure.
Symptoms. The trouble appears as prominent wedge shaped, reddish-brown spots extending inwards from the cleft of the pinnae. Affected plants take on a variegated appearance and are less luxuriant, but otherwise seem healthy. According to Clinton the scorching may not necessarily be the effect of burning by the sun's rays. It seems, nevertheless, due to the loss of moisture from drought caused by poor watering or to sudden changes of humidity in the air. The fern Adiantum farleyense is very delicate, and its thin leaves are more sensitive to unfavorable conditions.
Caused by overwatering or too much nitrogen in the soil.
Symptoms. Diseased plants lose their green color and turn white. Growth ceases and all leaflets eventually drop off (fig. 54).
Control. In repotting the plant into new soil it outgrows the disease.
Caused by Pythium intermedium De By.
This disease attacks young fern prothallia. The latter turn soft, limp, and darker in color than the healthy ones. In general structure the organism resembles Pythium de Baryanum. It differs, however, with regard to the zoospores. As worked out by Atkinson* the zoospores in P. intermedius are broadly fusoid, with pointed ends, and terminating at each end in a long cilium. After moving about for five to ten minutes, it gradually comes to a rest, the body undergoing plastic movement until the organism is cut into two parts, forming now two zoospores oval in form and each with a cilium attached directly at the smaller end. This peculiarity makes this organism different from Pythium de Baryanum. For control method soil sterilization is recommended (see pp. 32-43).
COMPLETORIA DAMPING OFF
Caused by Completoria complens Lohde.
Symptoms. The disease attacks young fern prothallia. It is manifested as a yellowish or yellowish-brown color of the prothallia as they lay on the soil in the bed or pot. A careful examination will show that the prothallia are spotted, the spots varying from yellowish-green to yellowish-brown, changing to deep brown and to black. In an advanced stage, a prothallium will present a checkered or mosaic appearance. As rot sets in, the prothallium becomes ragged and torn.
The Organism. The causal organism was studied by Atkinson. The mycelium of the fungus is made up of compact clusters of oval or curved branches originating from a common center. This vegetative body occupies a single cell of the affected prothallium, later putting out a slender germ tube which pierces the adjoining intervening wall, forming clusters of oval mycelial branches which become rounded and play the part of resting spores. Each of them may germinate by sending out a short germ tube at the tip of which a conidium is formed. When mature, the latter breaks off and is capable of germinating. Upon coming in contact with the host the conidia germinate by sending out a flask-shaped tube which comes close to the wall of a cell. The protoplasm of the conidium now migrates into the inflated germ tube. The latter produces a slender tube which bores its way into the cell of the prothallium, where it swells and grows in a fashion previously described (fig. 55, a to d.). Completoria complens attacks prothallia of the following ferns: Aspidium (Cyrotominum) falcatum, Pterisargyria, and Pt. cretica. Very little is as yet known of its method of control.
PHYLLOSTICTA LEAF SPOT
Caused by Phyllosticta pteridis Hals.
Symptoms. Ornamental ferns, such as Pteris cretica var. Magnifica are especially susceptible. The first symptoms of the spot disease is loss of the normal green in the frond. This is soon followed by the appearance of the ashy-gray spots surrounded by a border that is either purple or brown. Within the spot are found minute black pimples, which are really the pycnidia or fruiting sacs of the fungus.
The Organism. Phyllosticta pteridis was first described by Halsted in 1893. Since that time the fungus has received no further attention from plant pathologists, hence little is known of its life history. It is probable that spraying with Bordeaux mixture will protect the healthy foliage.
ALGA PARASITES ON FERNS
Caused by species of Oscillatoria.
In damp houses and overwatered soils, the prothalia of ferns are often overrun by certain algę which chokes them. This is accomplished by shutting out the air and light, interfering with their development and causing them to be completely sterile. As a result, many of the prothalia die. As a control measure, soil sterilization is recommended, see pp. 32-43.
GARDENIA (Gardenia jasminoides)
Cultural Considerations. Gardenias are very sensitive and easily injured if the temperature falls too low during cold nights. By the end of August, it is advisable to maintain some heat at night so that the temperature may be maintained at about 65 degrees F. The plants require an abundance of ventilation. However, the ventilators should be opened gradually in the morning and closed like-wise towards the evening. During cloudy days of November and December, care should be taken not to overfeed the plants with liquid manure.
FUNGI ON GARDENIAS
Gardenias are apparently very hardy plants. The following are the recorded fungi : Fumago vagans Pers., Hemileia vastatrix B. and Br., Hypocrella gardenia Henn., and Sphaerella gardenia Cke.
GENISTAE (Cystisus racemosus canariensis)
Cultural Considerations. In the fall, the plants are started at a low temperature of about 55 degrees F. The plants are easy to grow and require no special care if proper attention is given to the ventilation and watering.
DISEASES OF GENISTAE
Genistę are very hardy plants. There is but one disease recorded by Kirchner on greenhouse plants. The causal fungus is Ceratophorum setosum Kirch., which causes a disease on leaves and young shoots of Cytisus.
GERANIUM (Geranium sp.)
Cultural Considerations. Geraniums are mostly grown as a pot plant to be sold for house or out-of-doors purposes. Geraniums are easily grown. All they need is a soil fairly rich and an abundance of ventilation. It needs plenty of water, but will rot when overwatered. This is especially true for the cutting bed.
DISEASES OF THE GERANIUM
The geranium, although a hardy plant, is subject to the attacks of several important diseases.
Symptoms. Dropsy is a serious trouble which is confined to the leaves (fig. 56, a) and petioles and blades. Upon the stems and petioles, it appears as peculiar corky ridges. On the blades, it appears as numerous watersoaked specks of a clear amber color when held up to the light. The disease may attack all the plants in the greenhouse. In this case, the older foliage shows best the watersoaked specks. Such leaves soon lose their normal green color, at first turning yellow in spots, then throughout. In extreme cases, although the affected plant forms the normal number of leaves, they remain dwarfed and puny, and are badly specked before unfolding. Plants spotted lightly often recover when removed out of doors. The disease is worst in the early spring, when it attacks, mostly, young potted geraniums. As a rule, the blotches and pimples are quite evenly distributed. The specks, however, differ in form. Some are very irregular in outline while others are almost circular.
Cause. Dropsy is favored by poor light, wet soil, and a high soil temperature. Dropsy may be looked for in late winter with long nights, short days and cloudy weather. This causes an excessive root action with results injurious to the plant.
Control. Dropsy may be controlled by providing a cooler, dryer soil, and by exposing the plants to the direction where they will receive the greatest amount of light and ventilation.
Caused by Pseudomonas erodii Lewis.
Symptoms. This disease was found by Lewis on greenhouse geraniums in Texas. It is not known how serious or how extensive the disease may appear to be in different parts of the country. It is to be assumed that it is more or less prevalent in every greenhouse where it has been spread about by infected plants or cuttings.
The disease attacks four varieties of ornamental geraniums and the symptoms are the same on all. On the leaves, the spots first appear as minute dots which are transparent through light. With age the spots enlarge, become reddish brown in the center with a colorless border, resembling much the frog eye spot of the apple (fig. 56, d and e.). There is also a tendency to form large spots between the principal veins. In this case, however, infection begins at the margin of the leaf and progresses in-wards. Spotted leaves may also become pale and drop off prematurely.
The Organism. Pseudomonas erodii is a short but rather plump rod with rounded ends, borne singly or in short chains of 2 to 3, active by means of polar flagella. It produces no spores, and liquefies gelatin.
Control. There seems no evidence that insects are in any way associated with the spread of the disease in the greenhouse. The causal organism lives in the soil and is spread about by the splashing of water during watering. By the removal of the diseased parts and by careful attention to the watering, the disease may be kept in check. The same disease also attacks the wild geranium, Erodium Texanum, which in this case may act as a carrier of the causal organism. This weed therefore should not be tolerated around greenhouses where geraniums are grown, nor should it be used in the compost soil.
Caused by Bacillus caulivorus Pr. and Del.
Symptoms. This disease was found by Gallo-way to be destructive to greenhouse geraniums. It attacks the stems which at first become soft and mushy and later turn black and shrivel (fig. 56, c.).
Cuttings are especially susceptible and rotting usually starts at the cut and works upward, destroying it entirely. Rooted cuttings are not as likely to be-come infected as those freshly made and planted. The disease is most prevalent where young immature cuttings are made, and where the soil has been excessively damp and the house poorly ventilated. Little is known of the causal organism.
Caused by Pythium de Baryanum Hesse.
This disease confines its attacks mainly to geranium cuttings. For a description of the causal organism and of methods of control, see p. 17.
Caused by Sclerotinia fuckeliana (De By.) Fckl.
Symptoms. Gray mold is manifested as dead brown spots on the leaves. Under moisture conditions, the gray moldy growth appears. This is but the Botrytis or summer fruiting stage of the fungus. The trouble is prevalent in leaky houses or where water is used in excess and the beds are poorly drained. By proper ventilation, and by careful watering the mold may be kept in check.
Caused by Coniothyrium trabuti Riza.
As far as is known this disease is not known to occur in the United States. It was first recorded by Ali Riza as attacking geranium leaves, causing them to dry and shrivel.
Caused by Orobanche minor J. Esm.
This parasite is frequently met with on clover in the fields. Its attack on greenhouse geraniums was first reported by Halsted. The seeds of this parasite germinate in the soil. Soon after its roots become attached to those of the geraniums. The growth of the broom rape is soon apparent as a purplish, erect stem with scale-like purplish leaves above the ground. Later a number of blossoms are formed along the unbranched stem. The attacked geranium becomes sickly in appearance (fig. 56, b.). Steam sterilization of the soil will kill the seed of broom rape.