The Role of Cropping Systems in Nematode Population Management

Crop rotation is one of the oldest and most important approaches to the con­ trol of nematodes that feed on the roots of annual crop plants. The value of rotations often was recognized long before their effects upon the dynamics of nematode populations and communities were considered. As specific nema­ tode problems were identified and their economic importance demonstrated, attention usually was given to crop rotations as a means of either preventing or rcducing crop losses attributed to these pests. In many cases, crop rotation became the conventional method for nematode control and was readily ac­ cepted by growers because they previously had been introduced to such man­ agement practices as a means of improving soil fertility and crop productiv­ ity. Early rotation schemes were aimed at the control of a single nematode species on a susceptible main crop. They were developed empirically on the basis of knowledge of nematode life histories and host ranges. Field experi­ ments involved the selection of suitable alternate crops and determination of the number of seasons between main crops needed to obtain the desired de­ gree of control. Evaluation of cropping systems was based mainly upon mea­ surements of root disease severity in, and performance of, the main crop at the end of its growth season. Little, if any, attention was given either to the performance of rotation crops or to effects upon nematode populations. Bes­ sey (5) found certain cropping systems to be effective in controlling root knot in susceptible vegetable crops. He concluded that success depended upon how well the rotation crops met these requirements: (a) prevent devel­ opment and reproduction of the parasite; (b) at least pay the expense of working the land, as well as rent, taxes, etc.; (c) enrich the land or at least not impoverish it; and (d) make such vigorous, dense growth as to choke out