This section is from the book "The Standard Cyclopedia Of Horticulture Vol2", by L. H. Bailey. See also: Western Garden Book: More than 8,000 Plants - The Right Plants for Your Climate - Tips from Western Garden Experts.
A species of nematode worm (Hetero-dera radicicola) lives parasitically in the roots of a wide variety of wild and cultivated plants producing enlarged knots or swellings. This disease is known as root-knot and is more prevalent in light soils. It is especially troublesome in greenhouses. The adult female worm is flask-shaped, .5 to 1 mm. in length, pearly white in color, and is found within the knots on the roots. Each female lays several hundred eggs. The young worms may continue within the same root or migrate through the soil to others. Nematode root-galls have been found on nearly 500 different species of plants. It is especially destructive to okra, hollyhock, Amarantus tricolor, peach, snapdragon, celery, heart-leaved basil, wax gourd, beet, rape, red pepper, balloon vine, melon papaw, catalpa, endive, watermelon, coffee, muskmelon, cucumber, squash, pumpkin, carrot, deutzia, California poppy, fig, soy-bean, pecan, morning-glory, lettuce, gourd, sweet pea, flax, tomato, tobacco, peony, ginseng, passiflora, petunia, tuberose, cherry, pomegranate, eggplant, potato, salsify, clovers, violet, Old World grape.
See page 1023. This pest may be controlled in greenhouses by the use of live steam to sterilize the soil or by a weak solution of formaldehyde, one part, 36 to 40 per cent formaldehyde, to one hundred parts water, applied at the rate of one to one and one-half gallons to every square yard of soil surface of shallow beds. After the application, the soil should be thoroughly stirred and planting should not be done till at least ten days later. Under field conditions, the problem is more difficult. The most feasible method is a system of crop-rotation in which an immune crop is grown for at least two years between susceptible crops. One of the most resistant crops is the Iron variety of cowpea. Clean cultivation should be practised so as to destroy all susceptible plants.