Evaluating a new non-fumigant nematicide fluopimomide for management of southern root-knot nematodes in tomato

The southern root-knot nematode (Meloidogyne incognita) is one of the most damaging diseases affecting tomato production in China and worldwide. There is an increasing need to find environmentally friendly non-fumigant nematicides of low-toxicity to manage M. incognita because of the phase-out of methyl bromide and restrictions on the use of highly toxic non-fumigant nematicides. Fluopimomide is a novel fungicide with a chemical structure similar to fluopyram, another fungicide exhibiting nematicidal properties. However, the nematicidal potential of fluopimomide to suppress M. incognita and its effect on tomato plant growth was hitherto unknown. In the present study, the nematicidal efficacy of fluopimomide was evaluated in vitro and under greenhouse conditions against M. incognita and its effect on tomato plant growth was determined. In vitro, fluopimomide had a high toxicity to second-stage juveniles (J2s) and eggs of M. incognita with median lethal concentrations (LC50) of 23.4 and 9.5 mg L-1 after 48 h exposure, respectively. Under greenhouse conditions, fluopimomide at 250, 500 and 1000 g ha(-1) was effective in reducing root galling at 30 and 60 days after treatment (DAT), with the value of the galling index being reduced by 19.3%-23.8% and 35.7%-52.7%, respectively, and increasing plant height, stem diameter and above-ground biomass. Fluopimomide at all rates significantly reduced populations of M. incognita in the soil by 26.2-46.5% and 65.6%-82.1% at 30 and 60 DAT, respectively, compared with the untreated control. Moreover, there were no significant differences in reduction of M. incognita J2s by fluopimomide at 1000 g ha(-1) compared to fluopyram or abamectin. Application of fluopimomide significantly increased plant height with or without inoculation of M. incognita, indicating that plant growth promotion was attributed to treatment with fluopimomide itself. Overall, fluopimomide demonstrated strong nematicidal activity in vitro against M. incognita, and application of fluopimomide effectively reduced root galling and the populations of M. incognita, meanwhile enhancing tomato plant growth under greenhouse conditions.