Submitted to: Soil and Crop Science Society of Florida Proceedings
Publication Type: Proceedings
Publication Acceptance Date: May 22, 2002
Publication Date: September 22, 2002
Citation: Wang, Q., Klassen, W., Handoo, Z.A., Abdul Baki, A.A., Bryan, H.H., Li, Y. 2002. Influence of summer cover crops on soil nematodes in a tomato field. Soil and Crop Science Society of Florida Proceedings 62:86-91.
Interpretive Summary: Nematodes are microscopic worms that cause a ten-billion-dollar crop loss in the United States each year. These losses will increase because the most widely used chemical pesticide used to kill soil 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. Cover crops are plants that nematodes will not infect; these plants can be grown to potentially reduce nematode numbers in soils. In this study, ARS and University of Florida scientists evaluate the effects of three legume cover crops on both harmful and beneficial nematode populations. The cover crops were sunn hemp, velvetbean, and cowpea. Control experiments included plots on which no plants were grown and plots treated with a common chemical mixture used to control nematodes, methyl bromide-chloropicrin. Tomato plants were subsequently raised on these plots, and the effects of the previous plantings with cover crops were compared to the controls. The results indicated that the cover crops suppressed populations of plant-parasitic nematodes yet resulted in increased numbers of beneficial soil nematodes. The results are significant because these nematode-resistant cover crops may be promising candidates as replacements for chemical nematicides in some tomato production systems. This research will be used by scientists developing new methods for safely controlling nematode-induced crop losses, particularly in fresh-market tomato production systems.
A field experiment was conducted to evaluate the effects on populations of nematodes in tomato plots, some on which three legume cover crops (sunn hemp, Crotalaria juncea; velvetbean, Mucuna deeringiana; and cowpea, Vigna unguiculata) had been grown, and some which had been kept as a weed-free fallow or treated with methyl bromide-chloropicrin (MC-33). At tomato flowering, weed-free fallow followed by MC-33 strongly suppressed populations of plant-parasitic nematodes. Sunn hemp strongly suppressed all plant-parasitic nematodes except Helicotylenchus spp. and Tylenchus sp.; velvetbean suppressed some plant-parasitic nematodes but not Helicotylenchus spp.; and cowpea strongly suppressed all plant-parasitic nematodes. In all treatments, however, populations of free-living soil nematodes thrived. At tomato fruit harvest time, the total numbers of free-living soil nematodes increased in all the treatments than plant-parasitic nematodes (eight-folds in cowpea, two folds in weed-free fallow plus MC-33 followed by some plant-parasitic nematodes (Helicotylenchus sp. and Pratylenchus sp.), 60% in sunhemp (with very little change in spiral and other taxa); and 10% in the velvetbean (with a modest build up of non-parasitic form Aphelenchus sp.). Nevertheless these nematode-resistant cover crops appear to be promising candidates as replacements for methyl bromide in tomato production systems.