Effects of Selected Marigold Varieties on Root-knot Nematodes and Tomato and Melon Yields

Field experiments were conducted at two sites in California to evaluate the effects of marigold genotypes Tagetes patula var. Single Gold and Tagetes hybrid var. Polynema on Meloidogyne incognita infestation, root-galling, and yields of tomato grown immediately after marigold. Marigold cultivars were compared with a fallow control and with methyl iodide fumigation of soil prior to cultivation of M. incognita-susceptible and M. incognita-resistant tomato. Tomato yields after marigold were ca. 50% higher than after fallow. Marigold Single Gold consistently reduced nematode infestation and galling of tomato roots. Results were not significantly different between methyl iodide fumigation or marigold Single Gold at one site, but methyl iodide outperformed both marigold varieties at the other site. At one site, where melon var. Durango was grown during spring and summer of the year following cultivation of marigolds Single Gold and Polynema, melon yield increases of 95 and 45%, respectively, were still obtained.