The devastating root-knot nematode Meloidogyne incognita can cause severe damage to field
and greenhouse crops. Due to high economic losses, alternative products are essential to replace
banned or strictly regulated nematicides that affect human health and/or the environment. Garlic
based products have been previously investigated as environmentally friendly nematicides and their
active substances, diallyl polysulfides exist as formulated nematicides on the market. We tested the
garlic-based nematicide NEMguard® DE as protective of tomato roots. In vitro evaluation of the
lethal concentration (LC) showed strong nematicidal activity with LC50 of 0.8 mg/mL after 96 h
and LC90 of 1.5 mg/mL. NEMguard® DE showed protective effect against M. incognita as a single
application in small pots and a second application further reduced root galling, significantly. Large
greenhouse trials were carried out in two consecutive years to test single and monthly applications of
NEMguard® DE. In both years, no controlling effect could be observed on M. incognita. We assume
that the silt content of the loamy sandy soil used had an effect on the polysulfides, inhibiting their
nematicidal effect. We conclude that further experiments are necessary to investigate the nematicidal
potential of NEMguard® DE under different soil compositions or as a different formulation.