Efficacy of Azadirachtin in the Integrated Management of the Root Knot Nematode Meloidogyne incognita on Short- and Long-Cycle Crops

**Background:** Root-knot nematodes (RKN), particularly Meloidogyne incognita, cause 12–15% of annual global crop losses. The EU Green Deal mandates a 50% reduction in synthetic pesticide use, driving interest in plant-based alternatives. Azadirachtin, a triterpenoid limonoid from neem seeds (Azadirachta indica), has a favorable toxicological profile and documented nematicidal activity, but its persistence on short-cycle crops had not been studied. This study compared azadirachtin and the synthetic nematicide fluopyram against M. incognita on lettuce (45-day cycle) and tomato (120-day cycle) in a commercial greenhouse.

**Methods:** The experiment was conducted in a cold greenhouse at Vitulazio (Caserta, southern Italy) with a slightly basic (pH 7.2) medium-texture soil. Soil was uniformly infested with M. incognita (initial population Pi = 0.8 J2/mL soil). Twelve plots of 38.4 m² each were arranged in a randomized block design. Lettuce cv. Manita and tomato cv. Gotico F1 were transplanted on 12 April 2021. The azadirachtin product (Oikos®, 2.4% azadirachtin A) was applied at 1.5 L/ha via drip irrigation in acidified water (6000 L/ha), preceded and followed by water irrigation (15,000 and 9000 L/ha, respectively). Treatments were repeated 3 times (lettuce) or 4 times (tomato) at 12-day intervals. Fluopyram (Velum Prime®, 400 g/L) was applied twice at 0.625 L/ha (2 days before and 15 days after transplant). Nematode soil populations were extracted using the cotton wool filter method; root gall index was scored on the 0–10 Zeck scale. Data were analyzed by ANOVA with Student–Newman–Keuls test (p ≤ 0.05).

**Key Results:** On lettuce (45 days), azadirachtin reduced the final nematode population (Pf) by 71% compared to the non-treated control (1.5 vs. 5.1 J2/mL soil), and fluopyram reduced it by 67% (1.7 J2/mL), with no significant difference between the two products. Root gall index was reduced by 47% with azadirachtin (3.9 vs. 7.3) and 51% with fluopyram (3.6 vs. 7.3). Lettuce yield increased by 36.7% with azadirachtin (112.9 kg/plot) and 31.1% with fluopyram (108.3 kg/plot) versus the control (82.6 kg/plot). On tomato (120 days), Pf did not differ significantly among treatments (azadirachtin: 17.8, fluopyram: 18.8, control: 19.8 J2/mL), all 18–23 times higher than Pi. Root gall index was slightly but significantly lower with azadirachtin (7.4) and fluopyram (7.2) versus control (8.8). Tomato yield increased by 38.2% with azadirachtin (18.1 kg/plot) and 36.6% with fluopyram (17.9 kg/plot) versus control (13.1 kg/plot). Azadirachtin also provided insect pest control: no Spodoptera littoralis infestation occurred on azadirachtin-treated lettuce (versus 3 deltametrin treatments needed in other plots), and on tomato, S. littoralis and Tuta absoluta appeared later (5 June vs. 29 April) requiring only 2 versus 4 insecticidal treatments.

**Clinical Implications:** Azadirachtin is an effective nematicide for short-cycle crops like lettuce, matching fluopyram's performance while adding insect pest control. For long-cycle crops like tomato, azadirachtin alone does not sustain nematode suppression through the full season, and integration with synthetic nematicides or non-chemical methods (solarization, biofumigation) is recommended. The product is suitable for organic systems and can be combined with biocontrol agents. Limitations include the single-site/single-season design and lack of dose-response data.