Tomato Culture: A Practical Treatise on the Tomato

by W. W. Tracy

Watering and ventilation are the two points that require especial skill. Watering should be done at midday, to allow the beds to drain before night, and only enough water for the thorough moistening of the soil should be applied. Ventilation should be given every warm day as the temperature and sunshine will permit, but the plants must be protected from rain and cold winds. Work the surface of the soil to permit aeration and do not crowd the plants too closely in the beds. If damping off develops something can be done to check it by scattering a layer of dry, warm sand over the surface, and by spraying the bed thoroughly with weak Bordeaux or by applying dry sulphur and air-slaked lime.

Bacterial wilt (Bacterium solanacearum Erw. Sm.).—This disease, which also attacks potatoes and eggplants and some related weeds, is one of the most serious enemies of the tomato. It is known to occur from Connecticut southward to Florida and westward to Colorado, but is most prevalent in the Gulf States, where it has greatly discouraged many growers.

Its most prominent symptoms are the wilting of the foliage and a browning of the wood inside the recently wilted stems. An affected plant wilts first at the top, or a single branch wilts, but later the entire plant yellows, wilts and dies. Young plants wilt more suddenly and dry up. The disease progresses more rapidly in plants that have made a succulent, luxurious growth, while those with hard, woody stems resist it somewhat.

The disease is due to the invasion of bacteria, which enter the leaves through the aid of leaf-eating insects, or through the roots. They plug the water-carrying vessels of the stem, shutting off the water and food supply of the plant. If the stem of a plant freshly wilted from this disease be severed, the bacteria will ooze out in dirty white drops on the cut surface.

Remedial measures entirely satisfactory for the control of bacterial wilt have not yet been worked out. The best methods to adopt at present are the following:

(1) Rotation of crops.—The field evidence is that this disease is in many cases localized in old gardens or in definite spots in the field. It appears also that the infection left by a diseased crop can remain in the soil for some time. It is therefore advised that tomato growers should always practice a rotation of crops, whether any disease has appeared or not, and that in case bacterial wilt develops they should not plant that land in tomatoes, potatoes, or eggplants for three or four years. The length of rotation necessary to free the soil is not known, but will have to be worked out by the individual grower.

(2) Destruction of diseased plants.—The bacteria causing wilt not only spread through the soil but are carried by insects from freshly wilted to healthy plants. Diseased plants thus become dangerous sources of infection, and it is evident that all such should be pulled out and burned. This is particularly important at the beginning of the trouble when the eradication of a few wilting plants may save the remainder.

(3) Control of insects.—To lessen the danger from spread of wilt by insects, the measures advised in the next chapter for the control of leaf-eating insects should be adopted. In this connection it should be mentioned that the use of Bordeaux mixture for leaf blights, as previously recommended, has an additional value in that the coating on the leaves is distasteful to insects and helps to keep them away.

(4) Seed selection.—Work done at the Florida experiment station indicates that resistant varieties may be secured, but there are as yet none in commercial use. This is an important line for experimenters to follow up. There is no proof that the disease is spread through seed from diseased plants.

Fusarium wilt.—This disease and the one following resemble the bacterial wilt so closely, as far as external characters go, that they are difficult to tell apart. The parasites, however, differ so materially in their nature and life history that the field treatment is quite different. There are also differences in geographical distribution that are important, for while the Fusarium wilt occurs occasionally throughout the southern states, it is known to be of general commercial importance only in southern Florida and southern California.