Diseases Of The Carnation
( Originally Published 1920 )
Cause, gas injury.
Symptoms. The trouble appears as a white or creamy coloring of the unrolled tender tips of the foliage (fig. 46, a). Occasionally, the white spots appear across the leaves a short distance below the tips. The cause of the injury is believed by Clinton to be due to gas rather than to spray injury. The trouble may be brought about by the fumes of sulphur or tobacco used as an insecticide or fungicide. The injury affects the tip because of the tenderness of the tissue there. The Enchantress is particularly susceptible to it. The secret of its successful control lies in the care exercised during fumigation.
Cause, gas injury.
Growers in the vicinity of large manufacturing plants are often troubled with what is called sleep of carnation. This trouble is especially common in cities where gas is used for illumination. The symptom of sleep is a closing inward of the petals (opened corolla). Once a blossom goes to sleep it never opens again. The investigations by Crocker and Knight f have shown that at least one cause of sleep in carnation is due to traces of illuminating gas (ethylene) in the surrounding atmosphere. This trouble has been overcome in floral establishments where lighting gas was replaced by electricity.
Symptoms. The trouble is usually manifested on the blossoms. It is brought about by the application of an excess of certain chemical fertilizers. Acid phosphate applied in large quantities seems to produce no injury. An excess of dried blood will produce blossoms which become soft and subject to sunburn if sprinkled during sunshiny weather. Later, such injured blossoms have their center petals bunched, and only a few others opening. Later, the buds fail to open, the foliage assumes a deep green color with abundant glossiness and a normal growth. If overfeeding is continued growth ceases. Plants thus affected may, however, recover with judicious feeding.
Overfeeding with potassium sulphate is decidedly unfavorable. The edges of the inner petals crinkle, brown spots appear, and often there is a withering of the edges of the petals, while the center ones fail to open, as though glued together. The unopened buds swell, and the pistil is commonly seen projecting one inch beyond the bud. Moreover, there is a retarded growth, the leaf tips begin to die, and the whole plant resembles a rosette.
SPLITTING OF BLOSSOM'S
Carnation growers often lose heavily from the splitting of blossoms just before they fully open. The investigations of Darner and others seem to show that the splitting is brought about by under-feeding. The moderate application of commercial fertilizers will not cause an increase in splitting and may cause a decrease.
The splitting of the blossoms may also be noticed on the row of carnations near the glass of the side benches. The cause, it is assumed in this case, is due to the more rapid drying of the soil of the benches nearest the glass. Growers often prevent this trouble by so placing the benches as to allow a walk between them and the side walls.
Symptoms. True yellows as described by Lam-key t appears as a yellowing (mottled chlorosis) on the leaves. The mottling is brought about by the presence of indefinite irregular blotches or flecks which meet and form yellow streaks. The mottling is more common on the younger leaves, and the streaks on the older ones. The yellow areas may become red or pink. The spots are never water-soaked and possess no watery margin. They are always sunken, and possess no definite center. The cause of the trouble does not seem to be associated with any parasitic organism, but is probably due to improper cultural conditions, the exact nature of which is unknown.
Control. The control for yellows, as recommended by Peltier is as follows : Every check which tends to lower the vitality of the plant should be avoided. Weaker plants are more subject to yellows than stronger ones. Cuttings should never be taken from plants showing yellows. They should be made, too, from plants in bloom rather than from stock plants. They should be rooted early and should not be permitted to remain too long in the sand after rooting. The later the cuttings are made, the longer they take to root, and the more susceptible they are to yellows. Young plants should not be allowed to become pot bound.
COHESION OF PETALS
Carnation growers are often troubled by what is generally termed cohesion of petals. The latter are well out of the calyx, but are stuck together. Often they are grown together to such an extent that it is impossible to separate them without tearing the tissue. The trouble was first described by Arthur, but the exact cause of it is as yet unknown.
Caused by insect sting.
Symptoms. The best symptoms of this disease are manifested on the younger, but full-sized leaves nearest the upper end of the stem. A casual glance at such leaves reveals little to the untrained eye. However, by holding them near the sunlight, small dots may be seen scattered. These dots have a faint yellowish color. Later the surface tissue dries and the dots assume a whitish, reddish, or purplish color, while the spots enlarge and become sunken (fig. 46, g.). Such spots are seldom dark colored in the center nor are they made up of concentric rings. With the increase of the spots, the leaves wither, but cling to the stems. The general effect of stigmonose is a premature yellowing and stunting of the plant. The vigor of the plant at the time of the appearance of the disease largely determines the severity of the injury. Strong plants will be-come spotted, but will in no other way greatly suffer from it. Weak plants of the same variety will be-come stunted, and in many cases seldom outgrow the disease.
The cause of the disease was first attributed by Arthur and Bolley to a bacterial organism Bacterium dianthi Arthur and Bolley. However, the investigations of Woods t show that stigmonose is caused by the stings of aphides, thrips, and red spiders. The irritant injected by these pests causes the cells to react and finally to collapse, resulting in the specking previously mentioned.
Control. The carnation is a plant which is naturally adapted to a dry atmosphere. Under such conditions in the greenhouse aphides, thrips and red spiders are at their maximum activity. To keep these pests in check fumigation with tobacco ex-tracts or hydrocyanic acid gas is resorted to. The use of the latter, however, cannot be recommended for all carnation varieties.
Caused by Uromyces caryophyllinus (Schrank) Wint.
Symptoms. The rust is readily recognized by elevated blisters or sori filled with brown spores. The sori are first covered by the epidermis of the host, but when they ripen the latter bursts open, liberating the mature spores. This disease is more prevalent in overheated and overwatered houses. Infection once established will usually destroy a large per cent of the plants and seriously cripple many others. The disease may be found on all parts of the plant except the roots. Carnation rust seems to be more prevalent in the states lying east of the Alleghenies. Few greenhouses seem to be entirely free from the rust.
The Organism. The fungus has two spore stages, the uredospores and teliospores, both of which forms greatly resemble each other. The AEcia are found on Euphorbia gerardiana in Europe and is recognized as AEcidium euphorbix-gerardianae Fisch. The rust fungus attacks not only the carnation, but several other species of the pink family.
Control. Some florists advocate the use of an aqueous solution of common table salt. This is to be applied as a fine spray. Investigations by F. C. Stewart have shown that salt solutions can neither prevent rust infection nor stimulate growth. Neither is it helpful to apply salt to the soil. Carnations are propagated chiefly by cuttings. The latter often carry the disease. It is, therefore, imperative that cuttings be taken from healthy plants. Maintaining the proper temperature and ventilation, as well as exercising care and judgment in watering, will help to keep this rust in check. Subirrigation is preferred to overhead irrigation to keep the plants dry. Progressive growers use an inverted V-shaped wire netting (one-inch mesh) placed between the rows. The wire is cut into strips of fifteen inches width. These are bent and inverted, about six inches high and eight inches wide, and placed between the rows of plants. This support to the foliage pre-vents it from touching the wet ground and admits at the same time perfect ventilation. It also makes it possible to water the soil without wetting the plants. The trouble may, of course, be avoided to a great degree by growing resistant varieties. The Scott and the Jubilee are two varieties very susceptible to rust. On the other hand, the Enchantress and the Lawson are highly resistant.
A Parasite of Carnation Rust. Most parasites have others to live on them. The carnation rust seems to be no exception. The fungus Darluca filum (Bin.) Cast. was found by Blodgett to parasitize the carnation rust fungus. The presence of the Darluca is manifested by a dwarfed and weak development of the rust pustules. The pycnidia of Darluca (fig. 46, b and c) are found scattered on the rust pustules and are flask shaped, the spores are two-celled (fig. 46, e and f), colorless, and when ripe escape in masses of long tendrils, held together by a gelatinous substance in the outer cell wall of the spore (fig. 46, d.). The latter readily germinate in water. Darluca filum also attacks the asparagus rust fungus. It is possible to grow Darluca in pure culture and to inoculate its spores on the carnation rust fungus. In nature, however, it has not proved abundant enough to keep the rust in check.
SEPTORIA LEAF SPOT
Caused by Septoria dianthi Desm.
Symptoms. Leaf spot is characterized by light brown patches on the leaves and stems. On the latter, the .spots are usually found midway between the joints. On the leaves, infection seems to be more localized on the lower than on the upper half, and it is particularly frequent on the broad sheathing base of the leaf (fig. 46, h.). Affected foliage is often bent downwards. A leaf with numerous spots may be bent at various places, downward as well as sideways. The spots are usually indefinite in size and outline. Within the dead area may be found numerous minute fruiting bodies (pycnidia).
Caused by Oidium sp.
Mention of this disease is made by Mercer, who found it on greenhouse carnations in England. It has not yet proved of economic importance in the United States. This trouble appears as white, powdery patches on the leaves, calyx, and corolla. The English varieties most susceptible are "Lady Arlington," "Bridesmaid," and especially "British Triumph." So far only the conidial or Oidium (fig. 46, g) stage of the fungus is in evidence. The ascus or winter spore stage may probably appear on other hosts. The trouble may be kept in check by dusting with flowers of sulphur or by spraying with potassium sulphide as recommended for the rose mildew (see p. 323).
Caused by Sporothrichum pox Pk.
Symptoms. This disease seems to be confined to the floral buds only. Ordinarily the affected buds fail to expand or only open part way (fig. 47, a and b.). A close examination will show that the interior of the affected bud is browned and moldy. The rotted tissue may be found in the center of the bloom or on the petals. The stamens, styles, and pistils are also frequently affected. 'Where young buds are diseased the calyx, too, will be involved, otherwise it is usually sound, although the other parts of the flower may be decayed.
The Organism. The hyphæ are creeping, varying in thickness, hyaline, and septate. The conidia are of two kinds : Microconidia—one-celled, globose or broadly ovate; Macroconidia—abundant, one, rarely two, septate and several times larger than the microconidia (fig. 48, g to i.). Stewart claims that Sporotrichum pox Peck found on diseased tops of June grass and S. anthophilum, which causes the bud rot of carnations are the same. The fungus is spread about in the greenhouse by a mite (Pediculopsis graminum Reut.).
Control. According to Heald and others the most susceptible varieties to bud rot may be mentioned—the Lawson, Enchantress, Queen Louise, and Bradt. These, therefore, should be handled with more care. All diseased buds should be picked off and destroyed by fire. The temperature and moisture in the air should be kept as low as possible. The fact that the mite which is associated with bud rot (fig. 48, k to m) is also found on June grass would suggest the necessity of avoiding sod where this grass is common, in the making of the compost. This, however, may not be important when the soil is steam sterilized.
Caused by Heterosporium echinulatum Berk.
Symptoms. The disease becomes apparent as roundish spots, varying from a sixteenth to a sixth of an inch in diameter, and is found mostly on the tip of the leaves. In severe cases the entire leaf and even the major tops of the plant become spotted (fig. 47, c.). According to Halsted the color of the spots is pale ashy and covered with a fine, dense growth of the causal fungus, giving it the moldy appearance. Frequently the color changes to a gray shade, sometimes approaching dark brown.
ALTERNARIA LEAF SPOT
Caused by Alternaria dianthi Stevens and Hall. Symptoms. This trouble manifests itself as ashen white spots, the centers of which are occupied by a scanty or profuse black fungus growth, which is made up of the spores of the fungus (fig. 47, d and e.). The spots are dry, rather shrunken, circular or somewhat elongated. If the node of the stem is attacked, the disease spreads sufficiently to involve the adjoining foliage as well. The stem itself becomes somewhat girdled and in time is also killed. Usually, however, the spots are confined to the foliage.
The Organism. The mycelium is dark brown. (fig. 48, a.). The conidiophores arise from a stroma, usually from one to twenty-five in number, and each one to four septate (fig. 48, b, e and f.). The conidia are borne in chains (fig. 48, d.), and in structure are very typical of other Alternarias (fig. 48, d.). The fungus grows well on various culture media. On media poor in sugars, the mycelium and spores are lighter in color and smaller in size and diameter.
Control. All infected material should be collected and destroyed by fire. Spraying with a standard fungicide is also recommended. From the observations of Stevens and Hall, the variety Mrs. Thomas W. Lawson appears to be the most susceptible to this disease. As far as possible, this variety should be avoided.
Caused by Volutella sp.
Symptoms. The disease usually attacks the base of the lower leaves as well as the stems which are closest to the ground. The trouble is seldom found on the upper leaves, although they may present a sickly pale appearance. Anthracnose is a serious disease of young cuttings. Not infrequently the grower loses 50 per cent of his cuttings from this disease. These damp off very quickly under a great variety of conditions.
Caused by Volutella leucotricha Atkinson.
This disease seems to be confined mainly to carnation cuttings. The symptoms are not different from those of the damping off caused by other fungi. In this case, the causal organism, Volutella leucotricha, first described by Atkinson, is distinct from V. dianthi Hals. The mycelium of the former has a tendency to swell at the hyphal cells, producing a strong constriction at the septa. The conidia of Volutella leucotricha are considerably smaller than those of V. dianthi and the setæ are different in form and in color. In V. leucothrica they taper but little towards the free end, are blunt at the tip and many times septate, with the stroma light colored, while it is black in V. dianthi. The methods of control are the same as those for other damping off diseases (see p. 17).
FUSARIUM LEAF SPOT
Caused by Fusarium sp.
Symptoms. This form of leaf spot usually follows the injury caused by the rust fungus (Uromyces caryophyllinus). The variety Emily Pierson is especially subject to the attacks of this peculiar leaf spot. The spots are large, often occupying the entire width of the leaf. The diseased tissue becomes covered with a pinkish mold in the center of which are found minute spore clusters of the Fusarium fungus. Little is known of the causal organism. In controlling rust, the leaf spot will also be kept in check.
`BRANCH ROT," DRY STEM ROT, OR DIE BACK
Caused by Fusarium sp.
Symptoms. This troublesome carnation disease was first described by Sturgis. Attacked stems and branches wilt rapidly and the color of the leaves turns to a yellowish green. Dead stems remain firm, although wilted and shriveled. The bark likewise remains firm. The causal fungus seems to gain entrance through cuts or wounds. With cuttings the trouble may start at the base, causing them to dry up and to lose their normal color. The conditions which favor the disease are excessive rains in the summer when the plants grow out of doors. This favors a large, bushy, soft growth, with a consequently profuse topping, which opens the way to the disease.
Control. Peltier recommends the use of medium sized sturdy plants in preference to large, bushy ones. As much as possible, overcrowding should be avoided. During the first three months after the plants have been brought in, the temperature should be kept as low as the plant will tolerate. The syringing should never be given in the evening nor in the cloudy weather. It should be given on clear days in the morning so that the plants will be dry by the evening. In topping a plant, care should be taken to make clean cuts and to avoid leaving stubs. In gathering flowers, break them off at a node. Finally all diseased material should be pulled out and destroyed by fire.
Caused by Rhizoctonia solani Kuhn.
Symptoms. The disease is at first manifested by a yellowing of the affected plant or branch. A few days later actual wilting takes place. This is true only in sunny weather. During cloudy weather, the plant remains turgescent even though the stem may be badly rotted. The trouble is confined to the stem end or to the roots of the plants. Deep brown lesions usually precede the rot and indicate the places where infection started. High temperatures and deep planting favor the disease. Of the older varieties, the following are reported as being especially susceptible to stem rot : Crimson King, Scott, Jubilee, La Purité, De Graws, Servan, Silver Spray, Flora Hill, McGowan, Portias, Boston Market, Craig, Lawson, Winson, and Lady Bountiful. The newer varieties do not seem to possess any more resistance than the older ones. For a description of the causal organism and methods of control.
Caused by Heterodera radicicola (Greef) Muller.
Symptoms. Root knot is characterized by swellings of the roots. Affected plants are decidedly dwarfed, yellowish, and sickly looking. The roots of diseased plants are extensively knotted, and lumpy. For a description of the causal organism and of methods of control.