This section is from the book "Commercial Gardening Vol4", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
These minute eel-like pests often play great havoc with Cucumbers and Tomatoes in market nurseries. They are the outcome of a pest known as Heterodera radicicola, and are hatched in the soil from minute eggs. About seventy-five of the young worms go to an inch when placed end to end, so that it requires a good lens to discover them.
The cause of the appearance of Eelworm seems to be due almost entirely to the superabundance of rich organic manure in the soil, and to overdoses of water and too high a temperature. Wherever soil has been highly enriched with large quantities of stable manure, and perhaps chemicals in addition, the Eelworms appear, being themselves no doubt the natural development from eggs laid in decaying organic material. Their presence undoubtedly indicates a sour or acid condition of the soil, which is fatal to the plants. The fibrous roots are invaded by the Eelworms, and in a short time become irregular warty necklaces, partly exposed on the surface of the soil, as shown in the sketch (fig. 473).
Many remedies have been tried to extirpate the Eelworm disease, and although some at first have apparently checked its advance, it is only for a short time. Carbolic solutions and sulphate of copper applications have proved useless, and every other suggested remedy, including naphthalene and solution of permanganate of potash, so long as erroneous cultural methods prevail. These consist in having a soil too rich in humus, and then rendering it sour and devoid of oxygen by the application of too much water, in addition to which may be mentioned too high a temperature (over 90° F.), and a stuffy atmosphere due to bad ventilation. By altering these things, and using a little basic slag or slaked lime to neutralize the acidity of the soil, there will not be much trouble from Eelworms. Once a soil is so badly infested with Eelworms, the only remedy seems to be to clear it out of the house, mix plenty of lime with it, and store it up in a heap for some months until it becomes once more sweetened or oxygenated (in other words "sterilized") by exposure to the weather. If used too soon for other crops, such as Carnations, bulbous plants, etc, the pest is likely to attack these, especially if grown under glass.
Fig. 473. - Cucumber Roots infested with Eelworms.