Greenhouse - The Radish
( Originally Published 1920 )
Cultural Considerations. There are few green-houses near a large city which do not force radishes. The radish more than any other plant thrives best in full light. Shade favors the development of foliage over root. The varieties best liked by the market are those of the Scarlet Rose type. A light sandy soil which contains sufficient humus is ideal for forced radishes. Radishes need plenty of water. However, overwatering may favor damping off. The most favorable temperatures are 43 to 45' degrees F. at night and about 55 to 62 degrees during the day. In warm days the ventilators should be fully open. On cold days they may be opened a little at a time. Radishes are often intercropped with lettuce or cauliflower.
DISEASES OF THE RADISH
Radish is subject to many diseases in common with the cauliflower and numerous other crucifers.
CLUB ROOT, see CAULIFLOWER, p. 122.
Caused by Pseudomonas campestris P Ew. Sm.
Symptoms. Black rot on radish is confined mostly to the tender white-rooted varieties, especially the Icicle. The black-rot germ penetrates the lateral feeding rootlets, from which it works its way into the main root. In cutting across a diseased radish, its interior fibrovascular bundles are found to be blackened. Such radishes are useless for the market. The disease seldom attacks the red or the black-skinned varieties. For further consideration see Black Rot, p. 124.
Caused by Actinomyces chromogenus Gasp.
Scab is not a common field disease of radishes. It is, however, found to be troublesome on the crop grown in greenhouses. The French Breakfast variety is commonly susceptible to the disease. The trouble may be expected if the crop is planted in a soil which previously produced a potato crop that was badly scabbed or where infected manure was used, or too much lime applied. For methods of control, soil sterilization with steam or formaldehyde is recommended (see pp. 32-43).
Caused by Rheosporangium asphanidermatum Ed.
Symptoms. The disease seldom attacks the leaves.
The injury is confined to the roots only. Diseased plants are flabby, pale or yellowish, with a tendency to wilt. The roots when pulled out will show that the rootlets have been rotted off and that the main root, too, has rotted at various intervals.
Control. This disease may be controlled in the same way as damping off (see pp. 32-43).
DOWNY MILDEW, see CAULIFLOWER, p. 127. DAMPING OFF, see RHIZOCTONIA, p. 20.
ROOT KNOT, see NEMATODE, p. 28.
Cultural Considerations. Rhubarb is a popular greenhouse crop, and is extensively forced for win-ter use. Greenhouse rhubarb is superior in quality and in texture to the out-of-doors variety. The plant may grow in total darkness, but a diffused dim light is advisable. The roots before being planted should be thoroughly frozen for a few days, then given a short rest. In the milder climates of the South, the roots should be dried before planting. Both of these treatments will accelerate growth. When well established the plants need not be watered more than twice a week. The temperature for rapid growth ranges from 50 to 55 or 6o degrees F. Under lower temperatures, the plants will re-quire a longer time to mature. The varieties which lend themselves well to forcing are the Paragon, Mammoth, Linnęus, Strawberry, and Victoria.
DISEASES OF THE RHUBARB
The Rhubarb is considered a very hardy plant. It is subject to but few diseases.
Caused by Peronospora jaapiana Mag.
This disease is fairly prevalent in Europe. Its presence in the United States is not definitely known. At any rate it is of little economic importance.
Caused by Puccinia phragmitis Schum.
Rust is a disease of little consequence. The ęcium known as AEcidium rubellum occurs on the rhubarb. The uredinia and the telia are found on Phragmitis. By destroying the Phragmitis the rhubarb rust will be prevented.
Caused by Vermicularia polygoni-virginica Schw. This disease is frequently found on old leaves of rhubarb grown out of doors. It is of little economic importance.
Caused by Ascochyta rhei E. and E.
Like anthracnose, this trouble is of little importance to greenhouse rhubarb. The causal fungus causes irregular spots, which fall out and give the affected foliage a ragged appearance.
SPINACH (Spinacia oleracea)
Cultural Considerations. There has developed lately a tendency to grow indoor spinach on a large scale. Growers who have tried it out find that it is as profitable a crop as lettuce. The cultural requirements of spinach are the same as those of lettuce, see p. 145. If the soil is deficient in nitrogen an application of nitrate of soda will be very beneficial. The aim should be to encourage rapid growth, which, moreover, insures high quality. Vigorous broad-leaved varieties such as Victoria, New Zealand, and others are recommended.
DISEASES OF THE SPINACH
Indoor spinach is generally subject to less diseases than that grown out of doors.
Cause : An excess of acidity or a lack of soil humus.
Symptoms. Malnutrition may be met with where commercial fertilizers are used to the exclusion of organic manures. The margins of the veins of the leaves become yellow while the central part takes on a mottled appearance. The outer leaves are usually the first to suffer; soon, however, the entire plant exhibits similar symptoms and ceases to grow.
Control. Where this disease is prevalent, the soil should be changed, or sufficient organic matter in the form of well rotted manure incorporated in the beds. Malnutrition as a rule is not prevalent in the greenhouse, for it is rare that a greenhouse soil is lacking in humus.
Caused by Peronospora effusa Rabenh.
Symptoms. The trouble is characterized by yellow spots of conspicuous, size on the upper part of the leaves. On the under side of the leaves, and corresponding to the spots above, is seen a mat come posed of the dirty white or violet gray fruiting bodies of the fungus. The disease is often prevalent in the field.
The Organism. Downy mildew is caused by the fungus Peronospora effusa. The spores of the parasite are borne on branches, which generally emerge through the breathing pores or stomata of the lower part of the leaf and germinate by sending out a slender germ tube. Infection takes place when the germ tube penetrates the upper side of the leaf, generally through the stomata. The winter stage or oospores may be found in the affected leaves.
Control. All infected material should be destroyed. Water should be withheld, and plenty of ventilation allowed whenever possible. The plants may be sprayed with a standard fungicide.
Caused by Colletotrichum spinaciae Ell. and Hals.
Symptoms. It appears as minute, round, water-soaked spots on the leaves. These quickly enlarge and become gray and dry. In the spots will be found evenly-scattered, minute, dark tufts; these are merely fruiting pustules which also contain minute black bristles or setoe. The disease is not limited to any particular part of the plant. Infection may take place anywhere on the foliage, stems, or petioles. The spore pustules may be formed on the upper as well as on the lower surface of the leaf. Under moist conditions, the pustules take on a salmon tinge, indicating that there is an abundance of spores formed at that time. The spores may be carried from leaf to leaf and from plant to plant by insects, wind, or rain water. In badly infected beds, picking should not be done when the leaves are wet. Infected material should be destroyed by fire.
The fungi Entyloma ellissii Hals, Phyllosticta chenopodii Sacc., Cladosporium macrocarpum Preuss, and Heterosporium variabile Cke. do not seem to trouble indoor spinach but are rather serious out of doors.