In vitro nematicidal activity of a garlic extract and salicylaldehyde to the potato cyst nematode.

The in vitro nematicidal effects of an aqueous garlic extract, salicylaldehyde, a nonylphenol ethoxylate surfactant and a formulation containing these constituents were evaluated against the potato cyst nematode, Globodera pallida. Newly hatched, infective second-stage juveniles (J2) were placed for 24, 48 and 72 h in solutions containing concentrations of the formulation from 30.080.0 μl l-1 with 20% (v/v) potato root leachate and sterile distilled water controls. The garlic extract, salicylaldehyde and surfactant treatments were assessed at concentrations proportional to their occurrence in the formulation. Hatching assays involved a series of experiments in which G. pallida cysts were incubated for 8 weeks in potato root leachate solution containing different concentrations of the test substances. A second set of experiments involved incubating cysts in different concentrations of the test substances for 2, 4 and 8 weeks prior to hatching in potato root leachate solution to determine how prior exposure to these substances influences hatching and in-egg viability. The formulation caused 100% mortality at 75.0 μl l-1 with an LC50 of 43.6 μl l-1 after 24 h exposure. Salicylaldehyde was the most toxic constituent of the formulation with an LC50 of 6.5 μl l-1 after 24 h, while the garlic extract achieved 50% J2 mortality at 983.0 μl l-1, demonstrating that the formulation and salicylaldehyde are more toxic to G. pallida in vitro than oxamyl but less toxic when compared with aldicarb. The surfactant showed no dose-dependent toxic effects on J2 when compared with the controls. Emergence of J2 from the cysts was significantly reduced by concentrations of the formulation above 688.0 μl l-1 and its equivalent concentration of salicylaldehyde, while concentrations of the formulation above 2752.0 μl l-1 and the corresponding salicylaldehyde concentrations resulted in complete irreversible hatch inhibition. Concentrations of the garlic extract below 137.6 μl l-1 caused 26% more J2 hatch in comparison to the potato root leachate solution. This study has shown that salicylaldehyde is more toxic to nematodes than the garlic extract, and is the first report of a hatch stimulatory effect of a garlic extract on G. pallida under in vitro conditions