Mode of action and ecotoxicity of hexanoic and acetic acids on Meloidogyne javanica

The main goal of the present study was to evaluate the hexanoic acid (HEX) and acetic acid (ACET), two active ingredients of the nematicidal Melia azedarach fruits water extract (MWE), for use on root knot nematodes control. We studied the effect of the acids on various growth stages of the phytoparasitic nematode Meloidogyne javanica , along with the phytotoxicity on tomato plants, their fate in soil and ecotoxicology, including non-target soil nematode and microbial communities. The EC 50/4d values established for paralysis activity on second-stage juveniles were 195 and 49 μg mL −1 for HEX and ACET, respectively. Both acids significantly inhibited M. javanica undifferentiated egg hatch and J2 release from free eggs immersed in 100 μg mL −1 solutions, but only HEX achieved activity when egg masses were treated with acids’ concentrations greater than 50 μg mL −1 . HEX lasted longer in soil than ACET did and yielded less females of M. javanica per gram of tomato root (EC 50 = 112 mg kg −1 ). Other than efficacy, the two acids had a negative impact on the free-living nematode abundances compared to the control, thus implying an eco-toxic character. MWE is effective for the target nematodes and increases the abundance of free-living nematodes and the microbial biomass.