Efficacy of Fluorinated Nematicides for Management of Root-knot Nematodes in California Processing Tomatoes

Abstract

California is the primary US producer of processing tomatoes. After decades-long excellent protection against the common tropical Meloidogyne spp. M. incognita, M. javanica, and M. arenaria (root-knot nematode: RKN) by Mi-resistant tomato cultivars, resistance-breaking RKN populations are spreading throughout the San Joaquin Valley. For some time, nematicidal crop management tools have diminished under CA State regulatory pressure. In recent years, new non-volatile compounds have been developed with novel modes of action. In this project with susceptible processing tomato grown on an M. incognita-infested site, the efficacy of three fluorinated nematicides was evaluated in 10 field trials from 2011 to 2021. Seven trials included fluensulfone, six included fluazaindolizine, and five included fluopyram. On average, tomato root-galling (0 - 10 scale) at harvest was reduced by 3.2, 2.3, and 2.5 by fluazaindolizine, fluensulfone, and fluopyram, respectively, compared to the untreated control. These reductions in root-galling corresponded with estimated yield gains of approximately 21%, 14%, and 15%, respectively, over the untreated control. The reproduction of RKN during the tomato crop was not affected by the nematicides. The tested compounds have a very low acute mammalian toxicity and are more target-specific than previous generations of nematicides. However, there is considerable concern about the persistence of synthetic per- and polyfluoroalkyl substances (PFAS) in the environment, including pharmaceuticals and pesticides containing fluorine with the C-F3 functional group.

Keywords: Meloidogyne incognita; PFAS; Solanum lycopersicum; fluazaindolizine; fluensulfone; fluopyram; management; oxamyl; root-knot nematodes; tomato.

Figure 1.

Correlation between reduction in tomato root-galling (gall_diff) and percent yield difference (yield_diff) relative to untreated control treatments from ten field trials. Line fitted according yield_diff = 0.63 × gall_diff² + 4.43 × gall_diff. adjusted R²=0.83.