Reniform nematodes that parasitize cotton and soybean can also reproduce on a wide spectrum of weed species, thereby maintaining nematode populations during the off-season. Microplot studies were conducted to evaluate the effects of three endemic weed species, morningglory ( Ipomoea lacunosa), hemp sesbania ( Sesbania exaltata), and johnsongrass ( Sorghum halepense), on reproduction of the reniform nematode, Rotylenchulus reniformison cotton (LA. 887) and soybean (Pioneer 96B21). Over two years of microplot trials, the co-culture of cotton with any of the three weed species suppressed numbers of reniform nematode juveniles in soil significantly. When grown singly, reproductive values of R. reniformis after 60 days on cotton averaged 69.0, while those for morningglory, hemp sesbania, and johnsongrass averaged 42.0, 23.5, and 18.0, respectively. Reproductive values on cotton co-cultured with morningglory averaged 38.5. Those for the cotton-hemp sesbania and cotton-johnsongrass combinations averaged 23.5 and 26.0, respectively. Nematode reproduction on soybean alone, and co-cultured with each of the three weeds, reduced reproduction of reniform nematode only in the presence of johnsongrass in two trials. Data from two subsequent 45-day duration greenhouse experiments conducted with cotton and leachates from each of the three weed species support the hypothesis that suppression of reniform nematode reproduction likely resulted from the secretion of allelopathic compounds by weed roots.
