Tomato Culture: A Practical Treatise on the Tomato

by W. W. Tracy

The health of tomato plants is to a large extent dependent on the conditions under which they are being grown. The character and physical condition of the soil, the supply of water and plant food, the temperature and amount of sunlight, are all factors of the greatest importance in the growth and development of the crop. When there are variations from the normal in the case of any of these the plant adapts itself to the change as far as possible, but its functions may be so disturbed as to result in ill health or disease. It is in many cases difficult to draw a line between a natural re-action of the plant to its environment and a state of disease. For example, the trouble described in the next paragraph seems to fall into the first class.

Shedding of blossoms.—The tomato is very liable to drop its buds and blossoms and in some instances partial or total crop failures have resulted. The principal causes are an over-rapid growth, due in many cases to an excess of nitrogenous fertilizers, unfavorable weather conditions, especially cold winds, continued rainy or moist weather, which hinders pollination, lack of sunlight, or extremely hot weather. Such shedding can be partially controlled by pruning away the lateral branches as soon as formed and topping the plants after the third cluster of fruit has set, and by a reduction in the use of nitrogenous fertilizers. A failure to set fruit in the greenhouse is often due to lack of pollination, which must be remedied by hand pollination.

Cracking of the fruit.—The formation of cracks or fissures in the nearly mature fruit is due to variations in the water supply and other conditions affecting growth at this stage. If after the development of the outer portion of the fruit has been checked by drought there follows a period of abundant water supply and rapid growth, the fruit expands more rapidly than its epidermis and the latter is ruptured. Some varieties of tomatoes are much less subject to this trouble than others and should be given preference on this account. The grower, so far as lies in his power, should seek to maintain an uninterrupted growth by thorough preparation of the land, by cultivation or by mulching. If the half-grown fruits are enclosed in paper bags, cracking may be prevented, but at the risk of loss of flavor in the ripened fruit.

Leaf curl.—The effect of pruning is to stimulate growth and to increase the size of the leaves, the effort of the plant being to maintain a balance between roots and foliage. With rapidly growing plants, especially in the greenhouse and garden where both high manuring and pruning have been practiced, more or less curling and distortion of the leaves may result without developing into serious trouble if the grower takes the hint and modifies his methods so as to permit a more balanced growth. On the other hand, the ill effects of over-feeding and pruning may reach a point where the plant is seriously crippled.

Edema.—Under certain conditions plants in greenhouses or even in the open field, may absorb water through the roots faster than it can be transpired through the leaves, with the result that dropsical swellings or blisters occur on the leaves and more succulent stems. There is also a deformation of the foliage, much like the leaf-curl produced by over-feeding. This trouble, known as edema, occurs when the soil is warmer than the air, or during periods of moist, warm, cloudy weather, which checks transpiration. The grower should cease pruning, and withhold water, and in the field cultivate deeply. In the greenhouse, adequate ventilation should be given, keeping the house dry rather than moist.

Mosaic disease.—The tomato is occasionally subject to a trouble allied to the mosaic disease of tobacco. It is characterized by a variegation of the leaves into light and dark green areas, usually accompanied by distortion and reduction in size. In severe cases a whole field may become worthless. While the nature of this malady is not fully understood, it is known to be due to a disordered nutrition of the young leaf-cells. It can be produced by severe pruning or by mutilation of the roots in transplanting, both of which should be carefully avoided. It is more likely to occur in seedlings that have made a soft, rapid growth on account of an excess of nitrogenous fertilizer or too high temperature. Close, clayey soils, on account of their poor physical condition, also favor the development of the disease after transplanting.

Western blight (Yellows).—In the North Pacific and Rocky Mountain states, serious losses are annually caused by a disease apparently unlike any eastern trouble. It is marked by a gradual yellowing of the foliage and fruit. Development is checked, the leaves curl upward and the plant dies without wilting. The nature and cause of this disease is as yet unknown. It appears to be worst on new land. Experiments that have been made indicate that in older cultivated fields thorough preparation of the soil, manuring and cultivation, combined with care in transplanting to avoid injuring the roots and checking growth, will greatly restrict the spread of this blight.

DISEASES CAUSED BY PARASITES

There are several fungous parasites of tomatoes, which, for the readers convenience, may be briefly mentioned and the treatment of all discussed together. The first three are indeed somewhat difficult to tell apart without a microscope, as they produce a similar effect on the leaves and all yield to the same treatment—thorough spraying with Bordeaux mixture.

Leaf spot (Septoria lycopersici Speg.) has been widely prevalent and injurious during recent years. It produces small, roundish dark-brown spots on leaves and stems. The lower leaves are attacked first and gradually curl up, die and fall off. The vitality of the plant is reduced and it is only kept alive by the young leaves formed at the top.