POPULATION RESPONSES OF PLANT-PARASITIC NEMATODES IN SELECTED CROP ROTATIONS OVER FIVE SEASONS IN ORGANIC COTTON PRODUCTION

Crops with resistance or tolerance to the root-knot nematode, Meloidogyne incognita race 4, were evaluated for management of plant-parasitic nematodes in organic cotton production for five consecutive seasons. During the first two summers, Sesamum indicum L. (sesame), Tagetes erecta L. (marigold), Crotalaria juncea L. (sunn hemp), Avena sativa L. (oat), and Gossypium hirsutum L. (cotton) were grown. During the winter, oat followed sesame, marigold, sunn hemp, and one of the cotton regimes, while the summer oat was followed by Crambe abyssinica Hochst. ex R.E. Fries (Abyssinian crambe) during spring. The other cotton regime was left fallow during the winter. During the third summer, cotton was grown in all the rotations. The results showed that rotations such as sesame/oat, marigold/oat, and sunn hemp/oat can be beneficial in reducing M. incognita race 4 population densities. Pratylenchus zeae population densities increased following sunn hemp in summer. Cotton is not a good host for this lesion nematode species. Cotton in the sesame/oat rotation gave a higher yield than in the other rotations. Development of effective crop rotation systems becomes difficult when crop choices increase and fields are infested with multiple plant-parasitic nematode species.