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Two strains of the fungus Verticillium lecanii (A. Zimmermann) Viégas were studied as potential biocontrol agents for root-knot nematode (Meloidogyne incognita (Kofoid & White) Chitwood) on cantaloupe (Cucumis melo L.). For the study, pots were filled with soil that had been inoculated with M. incognita (inoculum was applied at two levels: 1000 and 5000 eggs/pot). Each fungus strain was applied individually by pouring an aqueous suspension (made from a wettable granule formulation) into the inoculated soil. Controls received water only. One cantaloupe seedling was then transplanted into each pot. Plants were grown for 55 days in the greenhouse, and then harvested and assessed for root and shoot growth and for nematode egg production. In pots inoculated with 1000 eggs/plant, neither fungus strain affected nematode egg numbers. At the 5000 eggs/plant inoculum level, both strains of the fungus suppressed egg numbers (counts were 28% and 31% less than water controls). Neither strain of V. lecanii affected the number of eggs embedded in root galls; the fungus suppressed nematode population numbers overall solely by affecting the number of eggs located outside of root tissues. Both fungus strains were also autoclaved and then applied to soil, to test for effects of nonviable fungus. In pots inoculated with 5000 eggs, application of one autoclaved strain resulted in a 35% suppression in egg numbers after 55 days, suggesting that the fungus produced a heat-stable substance deleterious to the nematode.

The biosolid soil amendment N-Viro Soil (NVS) and a Streptomyces isolate (S 99-60) were tested for effects on root-knot nematode [RKN (Meloidogyne incognita)] egg populations on cantaloupe (Cucumis melo). Application of 3% NVS (dry weight amendment/dry weight soil) in the soil mixture resulted in significant (P ≤ 0.01) suppression of RKN egg numbers on cantaloupe roots compared to all other treatments, including 1% NVS and untreated controls. Ammonia accumulation was higher with the 3% NVS amendment than with any other treatment. Adjustment of soil pH with calcium hydroxide [Ca(OH)₂] to the same levels that resulted from NVS amendment did not suppress nematode populations. When cultured in yeast-malt extract broth and particularly in nutrient broth, S 99-60 was capable of producing a compound(s) that reduced RKN egg hatch and activity of second-stage juveniles. However, when this isolate was applied to soil and to seedling roots, no suppression of RKN egg populations was observed on cantaloupe roots. Combining S 99-60 with NVS or Ca(OH)₂ did not result in enhanced nematode suppression compared to treatments applied individually. The results indicated that NVS application was effective at suppressing RKN populations through the accumulation of ammonia to levels lethal to the nematode in soil.

Mustard seed meals of indian mustard [InM (Brassica juncea)] and yellow mustard [YeM (Sinapis alba)], alone and combined, were tested for effects on tomato (Solanum lycopersicum) plants and for suppression of southern root-knot nematode [RKN (Meloidogyne incognita)] and weed populations. In the greenhouse, with all seed meal treatments applied at 0.25% total w/w soil, low tomato plant stands (up to 60% dying/dead) resulted from amendment with 3 YeM:1 InM, 1 YeM:1 InM, and YeM, applied right before transplant. Compared with untreated controls, low numbers of RKN eggs per gram root were consistently recorded from amendment with 3 YeM:1 InM. In a 2012 field study, incorporation of 1 YeM:1 InM (1700 lb/acre) resulted in lower tomato root biomass than fertilizer application (504 lb/acre), YeM or InM (each 1700 lb/acre). All treatments were applied with added fertilizer to achieve 100–102 lb/acre nitrogen, 7.4 lb/acre phosphorus, 74.7 lb/acre potassium, 6.0 lb/acre sulfur, and 1.0 lb/acre boron. The lowest numbers of RKN eggs per gram root (harvest 2012) were collected from plots amended with InM (1700 lb/acre), YeM (850 lb/acre), and 3 YeM:1 InM (1700 lb/acre), but the numbers were not significantly different from fertilizer only (504 lb/acre) controls. Highest and lowest tomato yields (numbers of fruit) in 2012 were recorded from YeM (850 lb/acre) and 3 YeM:1 InM (1700 lb/acre) amendments, respectively. In 2013, there were no significant differences among treatments in eggs per gram root or in tomato yields. No mustard seed meal treatment affected weed populations. At the tested rates, YeM seed meal showed potential for use in tomato beds but results were inconsistent between years.

Clove oil derived from the clove plant [Syzygium aromaticum (=Eugenia caryophyllata)] is active against various soil-borne plant pathogens and therefore has potential for use as a bio-based pesticide. A clove oil formulation previously found to be toxic to the southern root-knot nematode (Meloidogyne incognita) in laboratory assays was investigated in greenhouse studies for nematode suppression and phytotoxicity on vegetable crops. Phytotoxicity studies were conducted with 0.1%, 0.2%, and 0.3% clove oil applied to soil 0, 2, 5, and 7 days before transplant of cucumber (Cucumis sativus), muskmelon (Cucumis melo), pepper (Capsicum annuum), and tomato (Solanum lycopersicum) seedlings. Tomato seedlings were the most sensitive to clove oil. The 0.2% and 0.3% clove oil concentrations applied as drenches at transplant (0 day) were the most phytotoxic to seedlings of all the tested vegetable species, with only 0% to 50% seedling survival. Most of the clove oil concentrations applied as drenches at transplant decreased shoot heights and fresh shoot weights of all seedlings. Some applications of clove oil at 0.2% and 0.3%, applied 2, 5, or 7 days before transplant also significantly reduced shoot growth, especially of pepper and tomato. Greenhouse experiments evaluating suppression of nematode populations on cucumber were conducted with 0.10%, 0.15%, and 0.20% clove oil applied 7 days before transplant. Overall, plants inoculated with nematodes tended to have smaller shoots and heavier roots than plants without nematodes. Effects of clove oil treatments on nematode population densities were inconsistent between the two trials. In Trial 1, 0.10% and 0.15% clove oil decreased population densities compared with the carrier control. In Trial 2, nematode population densities were lowest in the water and carrier control treatments. The results indicate that, with the tested clove oil formulation and application times, southern root-knot nematode populations would not be consistently reduced with clove oil concentrations that were not phytotoxic to one or more of the tested vegetable crops.