Crotolaria spectabalis and marigolds, when planted as cover crops, tend to reduce some kinds of nematodes. The use of marigolds to repel nematodes from interplanted vegetables is not effective control.
A good garden mulch tends to reduce damage caused by nematodes.
Many organic gardeners approve of and use sprays and other preparations containing naturally occurring materials. Diatomaceous Earth comes from petrified sea life. Pyrethrin, rotenone, and ryania are examples of natural poisons from plant parts. These give some control to some insects under certain conditions.
Natural predators should be encouraged wherever possible; however, predators raised in captivity, then released into the garden area are usually ineffective.
Insecticidal soaps, made from fatty acids tend to work well for some insects under average conditions.
Insect traps, baited with phermone lures, work well in some instances. Many of these have sticky adhesives to catch insects.
Solar fumigation is effective in reducing some soil-borne problems such as nematodes. Refer to "Nematology Plant Protection Pointers", such as NPPP-17, for details.
This document is Circular 375, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida.