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Greenhouse - The Chrysanthemum

( Originally Published 1920 )



Cultural Considerations. Chrysanthemum cuttings should be thick, firm, have several joints, and be about three inches in length. If the cuttings within three weeks fail to make a good root system, they should be discarded as weak stock. A house temperature of 50 degrees F. and a bottom heat of 60 degrees is best suited for the cuttings. It is very unwise to allow the cuttings to remain in the propagating bed as soon as they start to grow. In trans-planting for the first time the soil should not be too rich. A good loam with very little rotted manure is all that is required by the newly rooted cuttings. As the plants are finally set in benches in the green-house (fig. 49) they need a rich soil, as they are heavy feeders. The benches need not be over five inches, the depth of the soil not over four inches. As the plants are first set out in the benches, it is advisable to water only around each plant. As they become well established the entire bed may be watered with safety. It should be borne in mind that the soil must be kept moist very uniformly. Sudden drying of the soil checks growth, and too much will cause the leaves to become yellow and sickly. On bright days, syringing the foliage is very helpful. This, however, should be done in the early part of the day, so that the foliage will be dry at night. Chrysanthemums are heavy feeders, and this should not be lost sight of.

DISEASES OF CHRYSANTHEMUMS

Chrysanthemums are subject to several important diseases. These often become so troublesome as to seriously interfere with the profitable culture of the plant.

CROWN GALL

Caused by Pseudomonas tumefaciens Ew. Sm.

This disease causes swellings on the crown and the roots of the plant. The trouble is seldom of any economic importance under greenhouse conditions. The causal organism attacks not only chrysanthemum, but also the daisy, geranium, sugar beet, poplar, willow, peach, etc.

BLACK SPECK

Caused by Pilobolus crystallinus (Wigg.) Tode.

The speck is often found on the leaves. Some growers believe this specking due to the accumulation of smoke settled on the leaves after fumigation. Others believe that it is due to a condensation of ammonia arising from fresh manure. As stated for a similar case on roses (see p. 321), the specking is due to the discharge of sporangia of Pilobolus crystallinus. The spore-bearing stalks of this fungus are possessed with a mechanism which throws off the ripe spores considerable distances. Being covered with a sticky substance, these spore masses readily adhere to anything standing in the way. The specking may be expected wherever manure is used as a mulch. According to Craig the trouble may be promptly stopped by a light application of air-slaked lime.

RUST

Caused by Puccinia chrysanthemi Rozc.

Symptoms. Rust may be readily distinguished from all other diseases of the chrysanthemums. It appears as tiny, rusty blisters the size of a pinhead. When several appear together the blister assumes a larger size (fig. 50, c.). At first, the blister is covered by the epidermis of the leaf. With age, however, the epidermis bursts and breaks away, exposing a brown powder which is made up of millions of spores of the rust fungus. On badly infected plants, the leaves may be all covered with the rust sori which nearly always appear on the underside of the leaf. It was previously believed that the rust of chrysanthemum was the same which attacks common weeds belonging to the same composit family as the chrysanthemum. However, the investigations of Arthur have definitely shown that the chrysanthemum rust attacks this plant and no other host. Uredospores from dandelions, burdock, oxeye daisy, when sown on the chrysanthemum failed to produce the rust. On the other hand, uredospores taken from the chrysanthemum and sown on chrysanthemum hosts reproduce the disease. The disease no doubt is brought in with infected plants, or cuttings made from a rusted plant.

The Organism. It is very strange that the uredospore stage (fig. 50, d) is the only stage of the chrysanthemum rust that is found in the United States. This makes the fungus short lived unless it is continually transmitted from living chrysanthemum leaves to others. The uredospores are spherical to pyriform, possessing a spiny membrane and three germ pores. The teleutospores were mentioned and figured by Massee * and by Roze. However, without making cultures it is doubtful whether these claims can be accepted as final.

Control. It is claimed that the variety Queen is very susceptible to rust. It is also believed that pot-grown plants are less resistant to rust than are plants growing in benches. Hand picking, selecting of clean, strong stock, and inside culture are recommended to keep the rust in check. The chrysanthemum rust, although serious, need not be feared by the careful grower who selects his stock and who is careful about the watering and the ventilation of the house.

LIGULE ROT

Caused by Sclerotinia fuckeliana (De By) Fckl.

This rot in which the ligules become involved is often mistaken for a heart rot, and a destruction of the receptacle. The latter disease is brought about by nutritional disturbances. Ligule rot is caused by the fungus, Botrytis cinera, the fruiting summer stage of Sclerotinia fuckeliana.

Control. For ligulé rot Crepin recommends that the flower buds be sprinkled with a solution made up of two grams of chemically pure nitric acid to a liter of water.

BLOSSOM ROT

Caused by Sclerotinia fuckeliana (De By) Fckl.

Symptoms. This disease is usually confined to the blossoms only. The trouble first appears as minute discolored watery spots on the petals, giving the latter the appearance of having been pricked with a needle. The white-flowered varieties show the spotting more distinctly than the colored ones. The spots rapidly enlarge and involve the entire corolla. Diseased petals wilt, and are soon covered by a grayish, velvety growth (fig. 50, a), consisting of the summer fruit (Botrytis). After the first few flowers become affected, the trouble spreads rapidly and causes great damage. According to Spaulding* no one variety or color of chrysanthemum showed any difference in resistance.

Besides chrysanthemums the disease also attacks poinsettias (Euphorbia pulcherina). In this case the projecting angles on either side of the leaf become affected. It seems that with poinsettias, infection is localized in the broad green leaves which grow along the stems below the red zones. At the place of infection there is an exudation of small white drops of the hardened juice along the larger veins. These hardened drops of juice on the dead spots are very characteristic of the disease on poinsettias. Infected leaves drop off prematurely, thus marring the appearance of the plant. About two days after infection, the characteristic fruiting of the fungus makes its appearance.

PHYLLOSTICTA LEAF SPOT

Caused by Phyllosticta chrysanthemi E. and D.

Symptoms. The spots are orbicular, purplish brown with a distinct border. The trouble is mostly confined to the leaves.

Little is known as yet of the causal organism. It is probable that spraying with a standard fungicide will control the trouble.

RAY BLIGHT

Caused by Ascochyta chrysanthemi Stevens.

Symptoms. This disease attacks the buds or the opened blossoms. The affected blossom becomes brownish, straw colored, and withers. The discoloration nearly always begins at the base and works up to the tip of the blossom. Affected buds fail to open altogether. On opened flowers, the disease attacks on one side so that the rays in that direction will become destroyed (fig. 50, b.). The receptacle and the peduncle of diseased blossoms turn black and become shriveled. Portions of the stem may also be attacked, turn black and girdled.

The Organism. Ascochyta chrysanthemi was first described by Stevens. The pycnidia are few, occur singly or scattered about, and open by means of a short central ostiole. The spores are oblong, straight or irregular, hyaline, one septate, the ends obtuse or acute.

Control. All diseased material should be destroyed by fire. Careful and frequent spraying will control the disease.

SEPTORIA LEAF SPOT

Caused by Septoria chrysanthemi Cav., and S. chrysanthemella (Cav.) Sacc.

Symptoms. This disease usually appears as small dark brown spots which increase in size until they meet. Affected foliage drop off prematurely. Diseased plants become weakened and produce small flowers. The disease is often introduced in the greenhouse with infected cuttings. The pycnidia of the fungus are minute, while the conidia are obscurely septate.

Control. Cuttings should be secured from healthy plants. All diseased leaves and trash should be destroyed by fire. Spraying with a standard fungicide is also recommended.

BLIGHT

Caused by Cylindrosporium chrysanthemi E. & D.

Symptoms. This disease seems to work quickly and affected plants are short lived. The trouble appears on the leaves as dark blotches about one-half of an inch to three-quarters of an inch in diameter. The spore heaps are formed on the dead tissue where the spots occur. The area beyond the spot turns yellow, and soon the leaves shrivel, droop, and cling to the stems (fig. 50, f.).

The Organism. The acervuli of this fungus are imbedded, the conidia are somewhat thick but taper to the end; they are several septate and straight.

Control. Infected material should be destroyed by fire. Spraying, with a standard fungicide will protect the healthy plants.

POWDERY MILDEW

Caused by Oidium chrysanthemi Robh.

This is a very common trouble of indoor chrysanthemums. Affected leaves become covered with a powdery white growth. It seems that the Oidium or summer stage is the only one that occurs on affected plants. The winter or ascus stage has not yet been recorded. The trouble may be controlled in the same way as the rose mildew (see p. 323). Some growers prefer to use sulphur by mixing it with an oil and applying it to the steam pipes as a paint.

CINERARIA (Cineraria cruenta)

Cultural Considerations. The culture of this plant is very simple. However, it should be kept in mind that it is injured by hot dry air and sensitive to slight frost. The plant should be syringed practically every day, winter or summer. It also requires a cool shaded part in the house.

FUNGI RECORDED ON THE CINERARIA

The Cineraria, it seems, is very hardy. The fol-lowing fungi have been found on weakened or dead parts of the plant : Ćcidium cinerariae Rosti, Ascochyta fibricola Sacc., Coleosporium sonchi (Pers.) Lev., Leptosphaeria vagabunda Sacc., Puccinia eriophore Thum.

CLEMATIS

Cultural Considerations same as CYCLAMEN, p. 248.

DISEASES OF THE CLEMATIS

Clematis is a hardy plant. In the greenhouse it is subject to but few diseases.

ANTHRACNOSE

Caused by Glaeosporium clematidis Sor.

This disease was first met with by Sorauer on Clematis Jackmanni in Germany. It is not known whether this disease is present in the United States. Its introduction into this country should be carefully guarded against. Little is known of the causal organism. The disease may be kept in check by the destruction of diseased material.

LEAF SPOT

Caused by Cylindrosporium clematidis E. and E.

This trouble is manifested as reddish brown sub-angular to roundish spots on the leaves. The acervuli are immersed, scattered and few in numbers. The conidia are somewhat curved and when ripe exude in a white mass. C. clematidis, var. Jackmanni E. and E., also found on the clematis, differs from the former in the acervuli exuding a black mass of spores which are hyaline when looked at individually.

CoLEUs

Cultural Considerations same as GERANIUM, p. 260.

DISEASES OF THE COLEUS

Coleus is an unusual hardy plant in the sense that it is subject to so few diseases.

DAMPING OFF

Caused by Rhizoctonia solani Kuhn.

It seems that the variegated green varieties are more susceptible to damping off than the variegated red and yellow. Infected cuttings show lesions at the stem and above the surface of the soil. As the lesions spread and work in deeper in the tissue, the cutting topples over. For a description of the causal organism and methods of control, see p. 20.

BRoom RAPE

Caused by Orobanche ramosa L.

Coleus is often subject to the attacks of a broom rape. The trouble was found by Halsted and Kelsey on greenhouse plants. Orobanche, the broom rape genus, is of interest to greenhouse growers, because of its parasitic nature. Broom rape is a degenerate flowering plant. According to Harshberger the embryo of Orobanche has no trace of root and stem, but it consists of a spiral filament of delicate cells which feeds on the stored reserved food of the seed. Upon coming in contact with the roots of a suitable host it adheres itself closely and swells considerably, assuming a flask-shaped appearance. Secondary filaments are now produced from the flask-shaped body which bore in and penetrate into the vascular system of the roots of its host, where it receives its food. At the point of union between host and parasite, a bud is formed which later develops into a thick flower bearing stem which grows out above ground.

THE CROTON (Codiaeum variegation)

Cultural Considerations. Care should be taken not to allow the plants to become pot bound. The best foliage color is obtained when exposed to full sunlight. The plants do well in a moist house with frequent syringing of the foliage. The temperature at night should never be permitted to go down below 70 degrees.

DISEASES OF THE CROTON

The Croton is considered a very hardy plant, but one disease is of importance to the greenhouse man.

ANTHRACNOSE

Caused by Glaeosporium soraurianum All.

Symptoms. This disease is manifested as large yellowish-gray spots on the leaves, which become whitish, dry and brittle with age. The spots are more visible on the upper part, although they work down through the entire thickness of the leaf. The acervuli are usually formed within the spots and become apparent as salmon-colored, gelatinized dots. The causal organism resembles other Gloeosporium in structure. G. soraurianum is probably the same as G. crotonis Del., also found to attack croton leaves.

CORDYLINE (Cordyline australis)

Cultural Considerations. This plant greatly resembles dracenas. Cordylines are usually grown in pots. They require a warm moist atmosphere, and are sensitive to full light. However, during the fall they should be kept drier, and exposed to full light in order to better bring out the color of the foliage.

FUNGI RECORDED ON THE CORDYLINE

The plant is apparently very hardy. The following fungi have been recorded: Colletotrichum cordylines Poila., Macrophoma cordylines (Thum.) Berl. and Vogl., Phyllachora vervisegiua West., Phyllosticta cordylines Sacc. and Berl.



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