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Greenhouse - Parsley

( Originally Published 1920 )



Cultural Considerations. Parsley is easily forced and requires no particular care. Any of the curly-leaved varieties lend themselves to forcing.

DISEASES OF PARSLEY

Under greenhouse conditions parsley is subject to but few diseases.

DROP, see Lettuce, p. 150.

LATE BLIGHT, see Celery, p. 130.

PEA (Pisum sativum)

Cultural Considerations. Peas are seldom forced, although they could be easily grown in the green-house. No attempt should be made to grow them after March. They require a night temperature of 40 to 5o degrees F. and a day temperature of about 6o degrees. They are readily injured by higher temperatures. They thrive best in solid beds and re-quire an abundance of water and good drainage. The early dwarf varieties lend themselves well to forcing.

DISEASES OF THE PEA

Indoor peas may become subject to several diseases.

SCLEROTINIA rot (fig. 33), see LETTUCE drop, p. 15o.

THIELAVIA ROOT ROT

Caused by Thielavia basicola Zopf.

Symptoms. Plants severely infected with Thielavia have practically no root system, for the latter is destroyed by the fungus as rapidly as they are formed. All that is left is a charred, blackened stub. The diseased host constantly attempts to produce new roots above the injured part, but these in turn become infected. Such plants linger for a long time, but fail to set pods which are of any value.

The Organism. The mycelium of Thielavia basicola is hyaline, septate, and branched. The Mycelium becomes somewhat gray with age. Three kinds of spore forms are produced—endospores, chlamydospores, and ascospores. The endospores are so called because they are formed inside a special thread of the mycelium. This is the spore form that commonly occurs in pure cultures of artificial media and on the host. The endospore case is formed on terminal branches with a somewhat swollen base and a long tapering cell. The endospores are formed in the apex of this terminal cell and are pushed out of the ruptured end by the growth of the unfragmented protoplasm of the base. They are hyaline, thin walled, and vary from oblong to linear in shape. The chlamydospores are thick walled, dark brown bodies borne on the same mycelium as the endospores. This type of spore is formed in great abundance on the host and particularly within the affected tissue. The ascospores are lenticular in shape and are borne in asci or sacs within black perithecia. This stage, however, has not been found on the pea nor in pure culture.

Control. Since the causal organism is introduced with infected manure or soil, sterilizing the beds with steam or formaldehyde (see pp. 32-43) is recommended.

POWDERY MILDEW, see BEAN, p. 111.

POD SPOT

Caused by Sphaerella pinodes (Berk. and Bl); Niessl.

Symptoms. On the stem the trouble appears as numerous elongated lesions. These spread to such an extent as actually to girdle the affected stem. On the leaves are formed oval spots, grayish in the center, and limited by a dark band. The pods, too, become badly attacked and the symptoms there resemble those on the stems. The disease works its way from the pods to the seed within.

The Organism. The causative fungus has two spore stages. The pycnidia bear the hyaline, two-celled spores, and are formed within the dead tissue of the affected stems, leaves, or pods. The pycnidial stage is known as Ascochyta pisi Lib. The win-ter or ascospore stage has only recently been discovered by Stone, who found it on pods and stems previously affected, and on culture media. The fungus may be carried from year to year as dormant Mycelium within the seed, or in the ascospore stage.

Control. Seed treatment will not be of any value since the fungus is hidden within the seed. No out-side treatment is capable of reaching the parasite within. Seed should be secured from localities known to be free from the disease. Susceptible varieties, such as French June, Market Garden, American Wonder, should be discarded. The Alaska variety is said to be more resistant.

PEPPER (Capsicum annum).

Cultural Considerations. Peppers are not difficult to force, although they are not extensively grown on a commercial scale in the greenhouse. Peppers thrive best at a temperature slightly lower than that required by cucumbers (see p. 133). The Sweet Mountain variety seems to lend itself best to forcing.

DISEASES OF THE PEPPER

The pepper plant is considered comparatively hardy, and its few diseases usually become trouble-some only when, the crop is neglected.

SUN BURN (fig. 34, d), see p. 94.

ANTHRACNOSE

Caused by Glomerella piperata (E. and E.) S.

Anthracnose is a serious disease which is usually confined to the fruit. Its symptoms are characterized by round, soft, sunken, pale spots (fig. 34, a). The summer or conidial stage is known as Gleosporium piperatum E. and E. and is found as salmon colored pustules abundantly scattered over the spots. The ascospore stage may develop in pure, cultures of the fungus.

BLACK ANTHRACNOSE

Caused by Colletotrichum nigrum E. and H.

This form of anthracnose differs from the disease described above only in that the spots turn jet black. The trouble attacks the young as well as the mature fruit. The winter or ascospore stage of the causative fungus has not as yet been found. It is very probable that the fungus (fig. 34, b-c) is carried over as viable mycelium on the infected fruit left over in the field. Both forms of anthracnose may be controlled by spraying with Bordeaux mixture.

FRUIT SPOT

Caused by Macrosporium sp.

This disease, which is as important as anthracnose, attacks the fruit at the blossom end. The peppers that are attacked are half rotted, black, and moldy.

Little is known about the causative fungus. It is probable that the disease has the same origin as the blossom end rot of tomatoes, and that the Macrosporium fungus is only secondary. Spraying with Bordeaux mixture is recommended.

LEAF SPOT

Caused by Cercospora capsisi H. and W.

This disease is characterized by roundish raised spots on the upper surface, at first brown, later be-coming gray brown. They are limited by a dark zone, beyond which the leaf tissue is pale and chlorotic. Where the spots are abundant the leaves turn yellow, wilt, and fall off prematurely.

The conidiophores of the fungus are formed in clusters on both surfaces of the spots. The conidia are dilutely brown, clavate, and several septate. As a control measure spraying with Bordeaux mixture is recommended.

SOUTHERN BLIGHT

Caused by Sclerotium rolfsii Sacc.

Symptoms. Affected plants show a drooping of the young leaves at the tips of the branches. At night the plant seems to recover and it appears normal the next morning. This recovery, however, is only temporary. Wilting generally follows, and after three or four days the leaves become completely yellow, wilt, droop, and die. In another day, the stem of the plant loses its green color, dries up, and dies. On pulling out a plant freshly wilted, we find a shrunken discolored area at the foot of the stem, slightly below ground level. In more advanced stages, the shrunken area is covered by a delicate web of white mycelial threads, and after the death of the plant numerous brown mustardlike sclerotia are found on the surface of the affected tissue.

Control. The causal fungus is introduced in the greenhouse with infected soil or manure. Soil sterilization with steam or formaldehyde (see pp. 32.. 43) is recommended.



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