Greenhouse - Tomato
( Originally Published 1920 )
Cultural Considerations. The tomato is one of the three most important greenhouse vegetables. It is perhaps more difficult to grow than either lettuce or cucumbers. Great skill is required in the heating, watering, ventilating, and pollinating. To overlook any of these factors may result in failure. Of the numerous varieties which lend themselves to forcing the following are the most preferred by the American and English growers :
American Varieties English Varieties
The tomato thrives best in a medium heavy loam. The plants are heavy feeders. The fertilizer must be well balanced mixtures. The nitrogen, for instance, should not take the place of the potash or the phosphoric acid. Tomato plants require a liberal supply of water. However, overwatering will encourage numerous diseases. On bright, sunny days there is little danger of overwatering, but great care is required not to overwater during cloudy weather.
The temperature for greenhouse tomatoes is very important. At night and on cloudy days it should be maintained at about 6o degrees F. During bright, sunny days higher temperatures will not be harmful. The house should be given all the ventilation possible. Even during cold days, the ventilators should be opened slightly at frequent intervals while a close watch should be kept on the indoor thermometer.
DISEASES OF TOMATOES
Greenhouse tomatoes are subject to a large number of diseases. Many of these are of economic importance.
Symptoms. Hollow stem is a trouble manifested by seedlings in the bed, or after transplanting. The central portion of the head of the plant remains green while the lower leaves turn yellow. In severe cases, affected plants fall over as in damping off, with the absence, however, of signs of rotting.
Such plants when examined are found to have hollow stems and seem too weak to stand up.
Cause. There are several causes, any one or all of which may lead up to hollow stem. (1) A highly nitrogenous fertilizer applied to the seed bed to force the seedlings. (2) An abundance of water supply to make the fertilizer quickly available. (3) Sowing seeds of a rapid growing variety. (4) Transplanting without hardening off. (5) Transplanting into a dry soil.
Control. It is evident from what has been said that the fertilizer in the seed bed should be well balanced. Care should be taken to prevent the seedlings from becoming leggy, and to see that they are properly hardened before transplanting. The Stone and its related varieties seem to be more resistant to hollow stem. On the other hand, the Dwarf Champion seems to be especially susceptible to hollow stem.
Symptoms. This disease seems to be very prevalent on forced tomatoes in the United States and Canada. Howitt and Stone, who have recently studied this disease, describe it as follows : The leaves show distinct brown or blackened, angular, diamond-shaped spots scattered between the larger veins. When the spots are numerous and close together they appear as a distinct pattern. In a more advanced stage, the primary and secondary veins also become browned. Affected stems are peppered with minute brown lesions, irregularly scattered, and apparently superficially seated. In advanced stages, however, the lesions seem to work deeply into the vascular bundles. On the fruit the disease appears as surface lesions which are variously shaped. The surface of the spot may be unbroken and smooth, or rough and scabby. In advanced stages, the superficial lesions work in deeply in the flesh of the fruit. Upon maturing, the affected areas fail to take on the normal color. Such fruit is spotted and scabby, and is worthless for market purposes. Up to the present, the exact cause of the disease and methods of control are unknown. It seems that the trouble is not caused by a pathogenic organism, but rather by some unknown chemical or physical derangement of the soil.
BLOSSOM END ROT
Blossom end rot, also known as point end rot, may be found wherever tomatoes are grown. It is a disease of the fruit only. In some seasons fifty per cent or more of the fruit crop is ruined by it. It seems to be serious in dry weather and on light soils.
Symptoms. Infection is manifested as a water-soaked spot at the blossom end of the fruit (fig. 36, a.). The size of the spot may be that of a pin-head, or it may spread so rapidly as to involve half of the tomato. A few days later, the water-soaked spot becomes black and leathery and ceases to make further progress. Complete rotting of the fruit may be brought about by secondary invasions.
Plants subject to frequent slight wilting produce a greater number of defective fruits. There seems no doubt but that the water supply in the soil is an important factor in limiting or increasing blossom end rot. The factors of drainage and cultivation are, therefore, important considerations. Although dry soils and drought favor the increase of the disease, the state of health of the plant itself seems equally important.
The use of fertilizers, too, seems to influence the trouble. Heavy applications of manure or of pot-ash seem to increase the rot, as do fertilizers in the form of ammonium compounds. This is especially true on sandy loams. On the other hand, nitrate of soda or lime acts as a check. In controlling blossom end rot, the moisture of the air in the green-house seems also an important factor. On bright, sunny days, it is not advisable to keep the air dry. However, care should be taken not to keep the air of the house dry during the night, as this encourages numerous fungous diseases.
Tomatoes are often burned while they are on the vines by strong sunlight beating on the exposed fruit. This results in a scalding of certain parts, loss of color, and a local drying which produces white spots with a dry, peppery appearance. Such fruit is unfit for the market.
Control. In houses where sunburn is prevalent it is advisable to have the house shaded and to plant varieties that have a dense foliage.
A lengthy discussion on mosaic has already been given on p. 102. Mosaic on tomato is a common field and greenhouse trouble, conspicuous on stalks, fruit, and leaves. On the leaves it is manifested as a mottling of yellow areas on the tissue that causes the leaves to warp and grow unevenly. In severe cases the normal leaflets are replaced by a filiform or fern-like structure, with a striking dissected form. The blossom of the diseased plant usually drops off, and the few fruits that are set are small and de-formed.
Caused by Pseudomonas solanacearum Ew. Sm.
Symptoms. Infected plants usually wilt rapidly without losing their green color. In large leaves, the main axis is bent downward in a drooping way. With the young plants the stems and foliage also droop and shrivel. The vascular system of such plants is browned, indicating the presence of the causative organism within. Upon cutting across a freshly wilted stem, one observes that a dirty white to brownish white slime that is not sticky oozes out. In soft and rapidly growing plants, the whole pith is often converted into a watery slime. In tomatoes and eggplants the disease seldom attacks the fruit but is confined to the vegetative parts.
Southern wilt attacks not only the tomato and eggplant, but it also causes a serious disease on potato, tobacco, peanut, nasturtium, ragweed, impatience, and verbena, in the open.
The Organism. Pseudomonas solanacearum is a medium-sized rod, with rounded ends and motile by means of polar flagella. Pseudo-zoogloeæ are common in old cultures. No spores are formed; on agar-agar, colonies are white, then dirty white, after-wards becoming brown with age. The organism does not liquefy gelatine and produces no gas.
Control. All diseased plants should be carefully pulled out and destroyed by fire. The house should be given all the ventilation possible and water withheld for a while. Syringing of the plants should cease until the disease subsides. In watering care should be taken not to splash soil particles on the plant. All insect pests whether sucking or biting should be controlled, as these usually help to spread the disease. This trouble is likely to be prevalent in greenhouses in the Southern states.
DAMPING OFF. See PYTHIUM.
Caused by Phytophthora infestans (Mont.) De By.
Late blight is a disease of frequent occurrence on greenhouse tomatoes.
Symptoms. Affected plants appear as though killed by frost. The disease first shows itself as small blackened areas on the leaves, stems, and fruits. These rapidly increase in size and cause the premature death of the affected host. Fruits which may not show signs of disease will develop the trouble in transit if coming from infected houses.
The Organism. The mycelium of the fungus is hyaline, non-septate. As shown by Melhus and others, the mycelium may be carried from year to year within the infected tubers. In fact this is but one way by which late blight is distributed. Through the stomata of the infected leaf emerge the slender conidiophores bearing the ovoid conidia. According to Melhus the conidia of Phytophthora infestans may germinate either directly by a germ tube or by the production of zoospores as in Pythium. The best germination occurs at the optimum temperature, which lies between 10 and 13 degrees C. (50-57 degrees F.). The conidia may be killed by exposure for six to twenty-four hours to dry atmospheric conditions such as exist in an ordinary room. Frost which kills the top of the plants will also kill the conidia of Phytophthora. Light does not hinder germination and therefore has no inhibiting effect on infection. Investigation fails to show that Phytophthora in f estans produces sexual spores or oospores within the affected tissue of the leaf or tuber. However, Clinton succeeded in developing what appeared to be oospores of the fungus in pure culture on oat agar. The oogonia appear as swollen terminal heads, cut off from the main thread by a cross wall. The antheridium resembles that of P. phaseoli. Mature oospores have a medium thick, smooth, hyaline wall. How the oospores germinate is unknown.
Control. Late blight of tomatoes may be con-trolled by spraying. The best results are obtained by using 5-5-50 Bordeaux.
Caused by Phytophthora terrestria Sherb.
Buckeye rot is a disease which attacks the fruit. The trouble seems to be new and has been recently described by Sherbakoff. So far as is known, the disease has appeared. only in Florida.
Symptoms. The disease, as the name indicates, appears as pale to dark greenish-brown zonate spots on the fruit. The rot is hard and somewhat dry when the fruit is green, but becomes softer as the tomato ripens. It usually begins at a point where the fruit touches the ground, which is most commonly at the blossom end, and might be mistaken for blossom end rot were it not for the characteristic zonations.
The Organism. The mycelium is at first continuous, then septate. Conidia germinate by means of swarm spores. Chlamydospores are common, oospores frequent on cornmeal agar. Besides tomato fruit, P. terrestria causes a foot rot of citrus trees and a stem rot of lupines.
Control. Fruit destined for distant markets should not be packed as soon as it is brought in from the house. If possible it should be kept a few days to allow for possible rot to develop so that the affected ones may be culled out and destroyed. Spraying with Bordeaux mixture is also recommended.
Caused by Ascochyta lycopersici Brun.
This disease is of common occurrence but of little economic importance. It produces brown circular spots which enlarge and change to grayish brown in color.
Caused by Phoma destructiva Plowr.
Symptoms. On the fruit the disease is characterized by conspicuous dark spots on the side and at the stem end of both green and mature fruit. On the surface of the largest spots, numerous dark pycnidia may be seen. Besides attacking the fruit, the disease may also infect the foliage, causing dark spots which resemble those on the fruit. Affected leaves shrivel, droop, and sometimes drop off. The disease seems to be unable to attack potatoes or peppers.
The Organism. The mycelium forms a dense net-work of fungal threads within the host tissue. The pycnidia are subglobose, carbonaceous, smooth, slightly papillate, and with a distinct central pore. The pycnidia are scattered and few.
Caused by Septoria lycopersici Speg.
Symptoms. The first indications of the disease are minute water-soaked spots on the underside of the leaves. 'With time, these increase in size and become circular in outline with a definite margin. The spots become hard, dry, dark, and shrunken, and when numerous they coalesce into large blotches, involving the entire leaflets and leaves; the latter soon droop, dry, and cling to the stalk, until broken off by the wind or by any other jar. Within the spots are formed minute black, glistening pycnidia while the spores exude yellowish mucilaginous drops.
On the stems, the spots are similar to those on the leaves, although they are not so clearly defined, nor do they work in deep enough to form cankers. Spots may also occur on the calyx and on the fruit. The disease, however, is usually a foliage trouble. Of the more resistant varieties may be mentioned Mikado, King Humbert, Wonder of the Market, and Up to Date. Of the medium resistant varieties may be mentioned Alice Roosevelt, President Gar-field, Prelude, Ponderosa, and Magnum Bonum.
The Trophy and Ficarazzi are very susceptible varieties.
The Organism. The mycelium of Septoria lycopersici is hyaline and septate. The pycnidia are globose; the pycnospores are hyaline, needle-shaped, many-septate, and lose their vitality when exposed to ordinary room temperature for about four days.
Control. The disease often starts on the seedlings in the seed bed. It is important, therefore, to start with a clean seed bed soil. Seedlings should be sprayed with 4-4-50 Bordeaux before being trans-planted. In the house, the plants should not be worked when wet. Spraying with 4-4-50 Bordeaux is recommended.
Caused by Colletotrichum phomoides (Sacc.) Chester.
Anthracnose is a disease to which ripe tomatoes are especially subject. The losses are often considerable both in the house and in transit.
Symptoms. The spots are at first small, but they soon enlarge. They are discolored, sunken, wrinkled, with distinct central zones, closely resembling the anthracnose of apple. In moist weather, the spots become coated with a salmon-colored layer which consists of the spores of the fungus.
The Organism. In structure, C. phomoides is little different from other Colletotrichums. The setæ of the fungus are very numerous, thus giving the acervuli a black appearance. The conidiophores are short, and the conidia, oblong, hyaline and one-celled.
Control. Anthracnose depends upon a moist atmosphere for its activity. Spraying with Bordeaux is recommended.
Caused by Cladosporium fulvum Cke.
Leaf mold is very troublesome in the greenhouse. In some of the Southern States, however, it is found on field tomatoes also. The disease is favored by a damp, moist atmosphere.
Symptoms. The mold appears as rusty cinnamon, colored irregular, feltlike spots on the underside of the leaf (fig. 36, b), the upper part of which turns brown, then black. The affected foliage finally curls and dies.
The Organism. The conidiophores of the fungus break through the cuticle of the epidermis in a dense crowded mass. The conidia are few and are borne on the tip ends of the condiophores, which are sparingly branched and knotty. The conidia are elliptic. or oblong (fig. 36, c), septate.
Control. The effects of the disease are seldom disastrous if infection starts when the fruit has set and is well developed. An early infection when, the plants are still young may result in the failure of the crop. Careful and thorough spraying with Bordeaux 4-4-50 before the disease appears is recommended. Spraying should be done once every two weeks and should cease about five days before the fruit is picked. If the disease becomes well established in a house, spraying will prove of little benefit. In that case, the house should be emptied of all vegetation, the soil sterilized with steam or formaldehyde (see pp. 32-43), and wherever possible the house, too, should be fumigated with formaldehyde and potassium permanganate.
Caused by Macrosporium solani E. and M.
Symptoms. Black rot is a fruit, stem, and foliage trouble. The spots are black, dry, slightly wrinkled, and extend deep into the interior tissue (fig. 37, a and b.).
The Organism. The mycelium of the fungus at first varies in hue from hyaline to brown, then turns black. The conidiophores and conidia are dark, with three to six transverse and one to two longitudinal septæ (fig. 37, e.). Spraying with Bordeaux mixture is recommended.
Caused by Fusarium lycopersici Sacc.
Sleeping sickness is a tomato trouble. It is usually brought in with diseased seedlings.
Symptoms. Infected plants become pale, the leaves wilt and droop and never recover (fig. 38, a.). The droopiness of a diseased plant gives it a sleepy appearance, hence the name of the disease. On splitting open a diseased root or stem, one finds that the interior vascular bundles are brown, due to the presence of the parasite (fig. 38, b.).
The Organism. F. lycopersici is a soil fungus which may be introduced with infected manure or seedlings. The fungus greatly resembles F. oxysporum. The conidia are hyaline to yellowish, falcate, acute (fig. 38, c and d.).
Control. Spraying will not control this malady since the parasite lives internally and cannot be reached by external applications. The selection of resistant varieties may offer a means of conquering this trouble. Soil sterilization with steam or formaldehyde is essential.
Caused by Fumago vagans Pers.
Black mold usually follows the attacks of the white fly. The same fungus also attacks nasturtiums grown indoors. The fungus appears as a conspicuous olive-black growth on the upper part of the leaves. The fungus in this case is not parasitic, but usually grows on the honey dew secreted by the white fly. Although the fungus is not parasitic, its presence on the leaves is undesirable since it interferes with the absorption of light by the plant. In controlling white fly, the black mold fungus will also be checked.
RHIZOCTONIA FRUIT ROT
Caused by Corticium vagum B. and C. var. solani Burt.
This form of rot makes its appearance at the place where the fruit touches the ground. The diseased area becomes chocolate-colored, and the epidermis slightly wrinkled. The rot extends into the interior pulp, turning it brown and dry. For a further description of the causative fungus, see p. 20.
ROOT KNOT, see NEMATODE, p. 28.
Caused by Orobanche ramosa L.
The parasite fastens itself to the tomato roots whence it derives its food. The parasite produces a base of considerable size below ground from which a cluster of branching stems and bluish-yellow flowers appear above ground. The same parasite also attacks the hemp and tobacco out of doors.
FUMIGATION AGAINST WHITE FLY
The tomato is a favorite host for the white fly.
The different conflicting results obtained by growers in the fumigation treatment may be attributed to the use of widely different varieties of plants. The variations may also be partly due to tightness or looseness in construction of the greenhouse. Investigations by Warren and Voorhees have shown that tomato varieties such as Lester Prolific, Elongated Sparks, Earliana and Station Yellow recover from the first fumigation with almost no injury. Under the same treatment, Eclipse and Fragmore's Selected suffer lightly, while Stone, Lorillard, Beauty, Perfection, and Best of All become seriously injured. Tomato plants injured by night fumigation usually show no ill effect until about four o'clock the following day, when they wilt. If lightly injured the tops usually die. Fumigation for fifteen minutes with potassium cyanide, one ounce to each 1,000 cubic feet of glass, during the dark is satisfactory for indoor tomatoes. The house at that time should be cool and dry (fig. 39, a-c.).