Root-knot nematode-resistant alfalfa suppresses subsequent crop damage from the nutsedge-nematode pest complex

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Southern root-knot nematode [RKN, Meloidogyne incognita (Kofoid & White) Chitwood], yellow nutsedge (YNS, Cyperus esculentus L.), and purple nutsedge (PNS, C. rotundus L.) occur together as a mutually beneficial pest complex in sandy soils. All crops grown in infested soils are affected due to the wide host range of the nematode, the perennial life cycle of the nutsedges, their interactions, and few control options. Therefore, studies were established in fall 1997 and 1998 to determine the influence of growing a nematode-resistant or susceptible alfalfa (Medicago sativa L.) crop compared with cotton (Gossypium hirsutum L.) on these pests over 3 yr and during a subsequent rotation to a chile pepper (Capsicum annuum L.) crop. Nutsedge and nematode populations were reduced to nearly zero in plots planted with alfalfa, but remained at damaging levels in plots planted with cotton. Before planting pepper, plots rotated from cotton were fumigated with 1,3-dichloropropene (1,3-D) for nematode suppression according to standard practice. Pepper yields were over two times higher after the alfalfa compared with cotton. Nutsedge populations following alfalfa, regardless of cultivar, were initially very low but resurged to levels comparable to the cotton by the end of the chile growing season. Nematode populations following the resistant alfalfa were comparable to populations after fumigation of cotton plots and lower at the end of the chile growing season than populations following the susceptible alfalfa. The benefit of the alfalfa crop lasted for 1 yr; therefore, growers must consider long-term strategies for extending suppression of this pest complex.

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