Submitted to: Nematropica
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/23/2007
Publication Date: 6/1/2007
Citation: Wang, Q.R., Li, Y., Handoo, Z.A., Klassen, W. 2007. Influence of cover crops in rotation on populations of soil nematodes. Nematropica. 37(1):79-92. Interpretive Summary: Plant-parasitic nematodes are microscopic worms that live in the soil and cause an estimated ten-billion-dollar crop loss in the United States each year. These losses will increase because the most widely used chemical pesticide for killing nematodes will soon be prohibited from use. One approach to solving the problem of designing new, safe means of controlling nematodes is through the use of cover crops. These are plants that are either poor hosts for nematodes or otherwise reduce nematode numbers in agricultural soils. In the present study, ARS and University of Florida scientists evaluated several different cover crops or potential cover crops (two marigold species, Indian mustard, radish, sunn hemp, velvetbean, cowpea, and okra) in field and pot experiments to determine if the crops could reduce populations of the root-knot nematode, the most economically damaging nematode infecting vegetables in the United States. The scientists discovered that the two marigolds, sunn hemp, and velvetbean effectively suppressed root-knot nematode populations; but okra, Indian mustard, radish and cowpea did not. In addition, these antagonistic effects reduced nematode infections of the subsequent crops. The results are significant because they indicate that these cover crops offer promise as replacements for chemical nematicides in some vegetable production systems. This research will be used by scientists developing new methods for safely controlling nematode-induced crop losses.
Technical Abstract: A pot experiment was carried out in south Florida to elucidate suppressive or antagonistic effects of several cover crops grown in rotation on soil nematode populations. The crops were two marigolds, Tagetes patula L. 'Dwarf Double French Mix' (MI), and Tagetes patula L. 'Lemon Drop' (MII), Indian mustard (IM) [Brassica juncea], Radish (RD) [Raphanus sativus L.], sunn hemp (SH) [Crotalaria juncea L., 'Tropic Sun'], velvetbean (VB) [Mucuna deeringiana (Bort.) Merr.], a Meloidogyne-susceptible cowpea (CP) [Vigna unguiculata (L.) Walp, 'Purple Knuckle Hull'], and okra (OK) [Abelmoschus esculentus (L.), 'Clemson Spineless 80']. Eight rotation schemes each with 3 rotations were carried out from June, 2002 to December, 2003. Those schemes were MI-RD-MI, MII-CP-MII, IM-VB-IM, RD-MI-RD, SH-OK-SH, VB-IM-VB, CP-MII-CP, and OK-SH-OK, respectively. Marigolds, sunn hemp and velvetbean effectively suppressed the root-knot nematode Meloidogyne incognita, but okra, Indian mustard, radish and 'Purple Knuckle hull' cowpea were susceptible and did not. Furthermore, the antagonistic effect of the nematode- resistant crops persisted to reduce nematodes infestations of the subsequent crops. The results indicate that rotating marigold with other ornamental plants or nematode-suppressive cover crops, such as sunn hemp, with field or cash crops can substantially suppress nematode populations and benefit subsequent crops.