Greenhouse - Tulips
( Originally Published 1920 )
Cultural Considerations. Indoor tulips are grown in much the same way as hyacinths (see p. 266). As blossoms appear, they should be put under partial shade. The petals are very delicate and are subject to burning or wilting when exposed to direct sunlight.
DISEASES OF THE TULIP
Tulips are subject to few but serious diseases.
Blindness in tulips is a trouble which results in a failure of apparently normal bulbs to produce flowers (fig. 72, a.). A blind tulip is distinguished from a normal plant by having a leaf scale only. This condition is prevalent where bulbs of small size are used. The cause of blindness, which is being investigated by Stout, is still undiscovered. Tulip bulbs which have bloomed well the previous year may become blind the second season. These same bulbs, however, may again bloom the third season.
This would seem to indicate that blindness does not necessarily mean run-down bulbs. It is very likely that the treatment during the curing, storage, or planting to a certain extent predetermines blindness.
Caused by Ustilago tulipae (H.) Wint.
Like the tulip rust, the smut is of little or no economic importance. Very little is known about either the disease or the causal organism.
There are two kinds of rust on tulip leaves. Each of these is caused by two species of Puccinia, namely, P. tulipe Schw. and P. prostii. Very little is known of these rusts; fortunately, also, they are of little economic importance.
Caused by Sclerotinia parasitica Massee.
Symptoms. The rot seems to be confined to the scales of the bulb only. The plate as well as the roots remains unaffected. When a tulip bulb is cut open, the scales are found to be more or less softened, grayish, water-soaked, and the inner part to be more or less rotted. As the rot progresses, the outer scales become covered with a mold which forms olive brown, velvety patches (fig. 72, b.). This is made up of the summer spores of the fungus. Later, the outer scales become covered with small hard fungus bodies, sclerotia (fig. 72, d.). Besides the tulip, the same disease may also attack Narcissus pseudo-narcissus, Galanthus nivalis, and Crocus vernus.
The Organism. The causal organism has two spore stages, the summer stage, Botrytis parasitica Cavara (fig. 72, c), and the winter or ascus stage, Sclerotinia parasitica Massee.
Control. Since the causal organism is introduced with the soil, steam sterilization of the latter is recommended. All infected material should be destroyed by fire. Care should be given to the watering and ventilation.
Caused by Sclerotium tuliparum Kleb.
The rot of tulip bulbs which is caused by the above organism has not as yet attained economic importance in this country. Very little is known of the disease or of the causal organisms. Hopkins states that the sclerotia of Sclerotium tuliparum are much larger than those of Botrytis parasitica, the latter of which are small, the size of a pin head.
Caused by Sclerotium tulipae Lib.
This trouble was found by Seaver on out-of-doors tulips. It is doubtful whether it will prove a serious drawback in the greenhouse. The causal fungus causes a rotting of the bulbs, and seems also to be involved in at least one form of blindness. In the latter case, the fungus is found on the young bud which fails to develop and finally rots off. It is very probable that Sclerotium tulipae Lib., S. tuliparum Kleb., and S. bulborum, all of which have been found by various workers on tulips, are in reality but one and the same fungus.
THE VIOLET (Viola Odorata)
Cultural Considerations. With violets the form of the house is not of great importance. In general, however, houses devoted to violets should be constructed on the even span model. A three-quarter span house furnishes too strong a sunlight.
Violets require an abundance of fresh air. Solid beds are preferred to the raised ones. In a house twenty-two feet wide there should be three walks, two and one-half feet wide. Each of the two outer beds should be one foot and nine inches in width, while each of the two inner beds should be seven feet wide.
The temperature at night should never be raised higher than 45 degrees F. for the double flowered varieties, and 45 to 50 degrees F. for the single flowered varieties. The day temperature should never run higher than 6o to 65 degrees F. Violets thrive very poorly under high temperatures. If the mercury rises above 65 degrees, ventilation should be re-sorted to in order to lower the temperature. High temperatures force the plants to foliage with a deterioration in blossoms. Violets thrive in a soil that is moist but well drained. The soil should be watered enough to keep it moist at all times, but it should never remain saturated for any length of time. Violets should be given all the ventilation possible every time the weather permits it.
DISEASES OF THE VIOLET
Violets under glass are subject to numerous diseases. Success with this crop requires that these troubles be kept in check to a minimum.
CLADOCHYTRIUM ROOT ROT
Caused by Cladochytrium violae Berl.
This trouble is found in Europe, where it was first described by Berlese. It has not yet been re-ported in the United States. This disease is manifested as swellings on the roots. The parasite is intercellular with branched mycelial threads. The globose zoosporangium terminates with an open tube through which the zoospores escape. Resting or sexual spores have not been recorded for this species. It is not likely that it will become an active parasite of forced violets.
Caused by Peronospora viola De By.
Downy mildew produces indefinite spots on the leaves. In general appearance this trouble resembles that of the grape. The downy pale violet growth on the spot consists of a layer of the conidiophores. These are short, many times branched with small ultimate branchless. The conidia are short and elliptic.
Caused by Urocystis viola (Sow.) F. de W.
Symptoms. The disease produces prominent irregular swellings or blisters on root stalks, stems, petioles, and leaves. Soon the swellings rupture, exposing black-brown masses, and giving the affected plant a smutty appearance.
The Organism. The spore balls are reddish brown and oblong to partly spherical. The sterile cells are yellowish with age, but the fertile cells are red-dish to light brown. The chlamydospores appear in balls of 4 to 8 spores.
Control. Smut is usually brought in with infected cuttings or plants from out-of-doors. These, therefore, should be avoided. Infected plants should be destroyed by fire.
Caused by Puccinia viola (Schum) D. C. Symptoms. The rust is characterized by circular patches, the presence of which greatly distorts the attacked parts. All the three stages of the causal organism, ęcia, uredinia, and the telia are present on the same fungus.
The Organism. The ęciospores are orange yellow, subglobose, and finely warty. The uredospores are roundish and brown, possessing tiny warts. The teleutospores are black, elliptic to oblong, with thickened tip, and with a very slight constriction.
Control. Violet rust is most prevalent on out-of-door plants, especially on the wild varieties. The disease is not of economic importance on indoor violets.
Caused by Sclerotinia libertiana Fcl.
This disease causes a rot of the crown as well as of the runners. This trouble is common in the cutting bed in which case it produces a damping off. In either case, the affected parts become soft and slimy. The disease is found only in leaky houses, or in beds with leaky water pipes. Attention to these points will check the trouble. For further description of the causal organism, see lettuce, p. 151.
THIELAVIA ROOT ROT
Caused by Thielavia basicola (B. and Br.) Zopf.
Thielavia root rot is perhaps one of the most important troubles of greenhouse violet. The disease also attacks sweet peas, cyclamens, and asters.
Symptoms. Diseased plants are dwarfed, with crinkled foliage, of a sickly yellow color. A closer examination will show that the seat of the trouble is confined to the underground stems and roots. In damp soils the former are often cracked, distorted, or covered with water-soaked spots. On the roots occur numerous brown or black lesions which eventually girdle them. This girdling may take place at several points. Often the roots rot off (fig. 73, a), and all that remains is merely a short stub. The runners like the roots are often spotted or girdled in many places. The lesions first appear as a brown water-soaked spot which enlarges, the center becoming whitish and the margin black. On the leaf petioles lesions are often produced which are similar to those formed on the runners.
The Organism. Thielavia hasicola has several spore stages. The chlamydospores are composed of from four to eight segments (fig. 73, e and f.). The basal segments are usually empty. The others above are dark brown, with thick walls and are able to break up into individual cells each of which is capable of germination. Another spore type is the spore generating tube from within which are pushed out small cylindrical bodies with thin walls, that are known as endoconidia (fig. 73, c and d.). The latter too are capable of germination. The third spore form is the ascospores. These are borne in sacks within a main globose fruiting body known as the perithecium. The latter stage, however, is seldom found on diseased violets. The fungus is generally carried from year to year as chlamydospores in remnants of infected tissue in the soil or in the compost pile.
Control. The fact that the harboring of chlamydospores in the compost is one of the means by which the causal organism is brought into the greenhouse at once suggests soil sterilization as a means of control. This disease is often carried unconsciously with affected cuttings. From there the sand used for rooting the cuttings becomes infected. If the same sand should be used over again it will infect all cuttings planted there. Where there are no facilities for soil sterilization the grower should make it a practice to use virgin sand every year. However, a safer method is to disinfect the soil with formaldehyde. Reddick recommends the use of 1 pint of commercial formaldehyde (40 per cent pure) to 12 1/2 gallons of water. This solution is then used at the rate of 1 gallon to each square foot of bed space. Lime should not be used for violet beds, because lime favors the development of Thielavia. Careful attention should also be given to the watering of the plants. An excess of moisture in the soil favors the disease. It is doubtful that spraying will have any effect in controlling this trouble.
Caused by Glosporium viole B. and Br.
This disease attacks the edges of the leaves, starting as an irregular discoloration which extends in-wards. Affected foliage rots and becomes unsightly. The acervuli are thin and few in numbers ; the conidia are yellowish.
PHYLLOSTICTA LEAF SPOT
Caused by Phyllosticta viola Desm.
Symptoms. This disease is characterized by numerous circular whitish spots, averaging about an eighth of an inch in diameter. Often the spots run together and involve the entire leaf (fig. 74, a.). The pycnidia are found on the dead tissue of the spots. The disease is commonly found on out-of-doors violets, but it is also met with under green-house conditions. The same disease also attacks the pansy.
Organism. The pycnidia of the fungus are brown, minute, and numerous. The spores are minute and subcylindrical.
Control. It is probable that spraying with a standard fungicide will control the disease. All infected material should be destroyed by fire.
ASCOCHYTA LEAF SPOT
Caused by Ascochyta viola Sacc.
This disease is characterized by scorched appearing patches on the leaves. The affected plants soon become unsightly while the blossoms produced are stunted and valueless commercially. Little is known of the causal organism. Destruction by fire of dis-eased plants and diseased material is recommended.
Caused by Marsonia violae (Pass.) Sacc.
Symptoms. The presence of the disease is marked by numerous small raised, black or brown colored spots on the upper surface of the leaf (fig. 74, c.). The disease, so far as is known, is confined to the leaves, and has not yet proved to be very serious. Jones and Giddings believe that the disease was probably introduced from Europe with imported cuttings.
The Organism. Within the minute spots may be found the acervuli in which the spores are borne (fig. 74, b.). The spores are curved and one or two celled. The spetum is generally nearer one of the tips than in the center.
Control. The disease may be kept in check by spraying with a standard fungicide.
Caused by Zygodesmus albidus Ell. and Halst.
This trouble is generally manifested as a white flourlike coat over the leaves. Little is known of the causal organism, nor has it proven so far of any serious consequence.
Caused by Alternaria viole Gal. and Dors.
Spot disease is often known under the names of leaf spot, blight, smallpox, and rust. The disease constitutes a serious drawback to indoor violet culture. In 1900, the violet industry of Alexandria, Va., had been practically abandoned because of leaf spot. From five to eight years before the appearance of the trouble the glass area devoted to violet in that vicinity was estimated at from 50,000 to 75,000 square feet of glass. The term "violet disease" is the one generally applied by the average grower.
Symptoms. The disease attacks violets in practically every stage of their development. Even cuttings in the propagating bed are not immune from it. Generally plants which make rapid growth, but which are soft and succulent, are most subject to leaf spot. On the leaves the spots are at first small, but definite, usually circular, greenish, or whitish resembling the sting of some insect. The spots soon enlarge and the light central portion becomes surrounded by a narrow ring of discolored tissue, which is black or brown at first, but which fades as the spots become older (fig. 75, a.). Young spots are water soaked and semitransparent. In a few days, however, the spots become dry, bleached, yellowish gray to white or pure white. Occasionally young spots fail to develop, dry and fall out, leaving a shot-hole appearance. Usually there are several spots on ą leaf. These upon enlarging meet and coalesce, giving the appearance of large, white blotches. The spores of the causal fungus develop on the spot under moist conditions only.
The Organism. The fungus grows well on agar media, usually in concentric rings. The color of the mycelium is at first grayish white, but as the spores are formed the entire growth takes on an olivaceous tint due to the color of the spores. The conidiophores of the fungus are borne in clusters and are erect, pale olivaceous, and septate. The conidia are borne in chains on the tips of the conidiophores, and are flask shaped, muriform, and olivaceous.
Control. To control this disease it is necessary to have a clear idea of the factors which favor leaf spot under greenhouse conditions. Dorsett enumerates the following:
"1. Not keeping the houses or frames clean, fresh, and sweet by frequently repairing and painting them, and by removing and destroying rubbish of all kinds as soon as it appears.
"2. Not keeping the plants clean and in the best possible growing condition at all times.
"3. Not selecting stock from strong, vigorous plants that have been entirely free from disease.
"4. Not being careful to select only strong, vigorous, healthy stock from the cutting bed for planting in the spring.
"5. Not giving the proper attention to the selection and preparation of the soil, to date and method of planting, and to care and cultivation of the plants during the growing season.
"6. Not giving due consideration to the several varieties and their adaptability to the soil and lo-cation in which they are grown."
It is evident therefore that these are important points to which the grower must give careful attention. In addition and as far as possible preference should be given to those varieties which are resistant to leaf spot. Marie Louise, for instance, is a very susceptible variety. On the other hand, Lady Hume Campbell is said to be resistant.
Since the spores of the causal organism may be introduced with the soil, steam sterilization is recommended. Proper attention also should be given to the ventilation, watering, and heating of the houses.
CERCOSPORA LEAF SPOT
Caused by Cercospora viola' Sacc.
The trouble is characterized by large, dead, ashy spots on the leaves (fig. 74, d.). The centers of the spots are darker, due to the presence of the conidiophores. These are dark and short. The conidia are rod shaped, hyaline, long, slender, and many septate.
Caused by Fusarium viola Wolf.
Symptoms. This disease is characterized by a sudden dying of the plants. Upon pulling it up we will find slightly sunken areas on the stem just above ground. The root system is generally destroyed, with the exception of a small stub.
The Organism. Fusarium viola was first described by Wolf. The sporodochia of the fungus are borne within the stems. The macrospores are hyaline, cycle shaped, 3-5 septate. The microconidia are small, continuous; condiophores short.
Control. The disease is likely to occur where fresh barnyard manure is incorporated in the soil before planting. Care should therefore be taken to use only well rotted manure. Infected soils should be steam sterilized, or disinfected with formaldehyde.
WALLFLOWER (Cheiranthus cheiri)
Cultural Considerations. Wall flowers require a cool house, with a night temperature not higher than 45 to 50 degrees F. They thrive best when sup-plied with an abundance of water and ventilation.
Fungi recorded on the wallflower. The wallflower is considered a very hardy flower, and is easily forced. The following fungi recorded on this host may prove serious:
Cercospora cheiranthi Sacc., Peronospora parasitica (Pers.) De. By.