Chapter 7

Crop Rotation on Organic Farms

Mangement of Nematodes with Crop Rotation

Crop rotation utilizes crops that are a poor or non-host to the nematodes found in a field. These crops can either be plants that provide a secondary cash crop grown in between cycles of the primary cash crop, or they can be cover crops. In either case, nematode numbers are reduced simply because nematodes are deprived of a suitable host crop. This does not mean that nematode densities are reduced indefinitely, but a successful crop rotation should reduce nematode levels enough so that a following susceptible crop will produce sufficient yields and survive until the end of its regular growing season. Response of nematodes is greatly influenced by the cultivar of a crop plant species. Therefore, even if the same plant species is used, results may vary if the cultivar is different.

Nematodes Controlled by Crop Rotation

Growing a crop on which the nematode pest can’t reproduce is a good way to control some nematodes. For example, the sugar beet cyst nematode (Heterodera schachtii) attacks only a limited number of crops including cole crops (broccoli, Brussels sprouts, cabbage, and cauliflower) and related crops and weeds. Growing non-susceptible crops for 3 to 5 years reduces the sugar beet cyst nematode population to a level where you can grow susceptible crops again. Similarly, peanuts are generally rotated with cotton crops as peanuts are not affected by the southern root-knot nematode (M. incognita) and will reduce the damage to cotton in following seasons.

Nematode Supressive Crops

Crops that do not serve as hosts to problem nematodes are sometimes used as intervention crops. Rapeseed and mustard have shown insensitivity to infection by a wide range of parasitic nematodes and are commonly planted by organic farmers to “clean up” soil during winter months.

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