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In this study, entomopathogenic nematodes (EPN) isolated from cotton ecosystem viz., Steinernema carpocapsae (strain APKS2) and Heterorhabditis bacteriophora (strain KKMH1) were evaluated in formulations of alginate gel, talc, sponge and water concentrates. The survival or longevity of infective juveniles (IJs) in these formulations was evaluated under in vitro at storage temperatures of 5 and 25 °C. Simultaneously the virulence of these stored EPN infective juveniles (IJs) was evaluated against the spotted boll worm Earias vitella through in vitro bioassays. The results revealed that S. carpocapsae (APKS2) and H. bacteriophora (KKMH1) formulated in alginate gel survived 70-100% up to 3 months with 55-100% infectivity at 5°C and survived 52-100% with 42.5-100% virulence for 2.5 months at 25°C. In talc formulation, these EPN remained alive to an extent of 55-100% with 70-100% virulence at 5°C and stayed alive 45-100% with 52.5-100% virulence at 25°C for 2 months. In sponge formulation, EPN strains survived 55-100% with 67.5-100% infectivity for 7 weeks at 5°C, but with 50-100% survivals and 62.5-100% virulence at 25°C. EPN strain S. carpocapsae (APKS2) can be stored in water at 5°C up to 8 weeks with viability of 50% and infectivity 60%. At 25°C, it can be stored for 5 weeks with survival of 62% and infectivity of 62.5-100 %. It is inferred from the results that alginate and talc formulations at storage temperature of 5°C is better for long term storage of S. carpocapsae strain APKS2 and H. bacteriophora strain KKMH1. Thus, the results revealed that S. carpocapsae (strain APKS2) and H. bacteriophora (strain KKMH1) can be formulated in sponges for use within 2 months and can be kept as water concentrate if they would be utilized in 2-3 weeks.

Slow decline disease caused by Tylenchulus semipenetrans is a major threat to global citrus production. Identification of suitable bio-agents that can be applied through a drip irrigation system by growers becomes inevitable for successful citrus production. Hence, field experiments were conducted to evaluate the effect of different liquid bio-inoculants, such as Bacillus subtilis, Purpureocillium lilacinum, and Trichoderma viride delivered through drip irrigation system on acid lime trees naturally infected with T. semipenetrans. They were applied at 4 L/ha, and their effect was compared with that of the spot application of carbofuran 3G at 100 g per tree. All tested bio-inoculants substantially suppressed the population density of T. semipenetrans in soil and acid lime roots. Among the bio-inoculants, P. lilacinum with 54.9–74.4% and 53.4–74.3% reductions in population in soil and root, respectively, performed best, followed by B. subtilis and T. viride. The effect of P. lilacinum was comparable to that of the chemical standard check carbofuran in location I, but P. lilacinum surpassed carbofuran in location II. Survival in soil and colonization on acid lime roots by P. lilacinum was higher than by B. subtilis and T. viride. The egg mass parasitization by P. lilacinum was also 7.1–7.5 times higher than by T. viride. The suppression of T. semipenetrans by P. lilacinum led to an increase in the number of fruits (19.0–23.3%), fruit weight (20.2–22.3%), and fruit yield (35.4–40.3%) in acid lime trees. The cost–benefit ratio by P. lilacinum was also higher (1: 2.6–1: 3.0), whereas it was lower in carbofuran treatment (1: 2.3—1: 2.4). It is concluded that the delivery of liquid P. lilacinum at 4 L/ha through a drip irrigation system was highly effective and economical for the management of acid lime trees infected with T. semipenetrans under field conditions.

Summary There is a growing interest in the use of natural products for crop production and protection. Humic acid is a well-known bioresource that intensifies soil functions and improves crop productivity. This review article provides a synopsis of the humic acid-plant-nematode association and the prospects for using humic acid as an alternative to chemical control of nematodes. Humic acid is known to have toxic and antagonistic effects against many plant-parasitic nematodes, including Meloidogyne spp., Rotylenchulus reniformis, Radopholus similis and Helicotylenchus multicinctus. The required dose for getting significant nematode control ranges from 0.04 to 2.0% concentration. Delivery methods like soil application or drenching, seedling root dip treatment and foliar spray on leaves are effective for nematode control. Humic acid controls plant-parasitic nematodes through various mechanisms including killing juveniles, inhibiting hatching, reducing nematode infectivity and reproduction, and inducing systemic resistance. Humic acid is compatible with bio-inoculants such as Azospirillum spp., phosphobacterium, Bacillus megaterium, Pseudomonas fluorescens, Trichoderma viride, Glomus spp., Pochonia chlamydosporia, Purpureocillium lilacinum and T. asperellum. These attributes of humic acid show a promising potential for use in nematode control. However, further work on bio-efficacy against a broad spectrum of plant-parasitic nematodes is needed.

Field experiments were conducted to study the effect of different liquid bio-products such as neem seed kernel extract (NSKE), azadirachtin and humic acid delivered through drip irrigation system on acid lime trees naturally infested with citrus nematode, Tylenchulus semipenetrans. All the bio-products were applied at 4 L/ha twice at 30 days interval and their effect was compared with carbofuran 3G at 100 g/tree. All the tested bio-products significantly suppressed T. semipenetrans density in soil and acid lime roots. Among them, NSKE was superior that reduced T. semipenetrans population by 56.8–58.1% in soil and 46.4–56.2% in root. Azadirachtin was the next followed by humic acid. The effect of NSKE was comparable to the chemical standard check carbofuran in location I, but NSKE surpassed carbofuran in location II. Suppression of T. semipenetrans infestation and infection by NSKE lead to improvement in the number of fruits (21.3–22.3%) and fruit weight (17.4–20.8%) in acid lime trees. NSKE delivery through drip system resulted in 35.8–37.9% more fruit yield. The benefit-cost ratio was also higher in NSKE (1:3.7–1:4.8) where as it was lesser in carbofuran treatment (1:1.3–1:3.0).

The field efficacy of liquid formulations of Pseudomonas fluorescens, Purpureocillium lilacinum and Trichoderma viride was investigated against natural populations of potato cyst nematodes (PCNs) Globodera rostochiensis and Globodera pallida. Two field experiments were conducted using these biocontrol agents applied as seed treatment (ST) at 1 L t−1 of seed and soil drenching (SD) at 5 L ha−1. Their effect was compared with carbofuran 3 G at 1 kg a.i. ha−1. Results showed that all the tested biocontrol agents were capable to reduce PCN egg density or multiplication rate, root penetration and egg numbers cyst−1 at various levels. The biocontrol efficacy also varied according to their delivery method. P. fluorescens-ST was found causing the highest reduction of egg density (83.1–86.5%), multiplication rate (83.1–86.5%), root penetration (67.1–68.1%) and egg numbers cyst−1 (35.4–36.0%). Similar efficacy was observed in P. lilacinum-SD that reduced egg density by 80.9–85.0%, multiplication rate by 80.7–84.3%, root penetration by 62.0–64.4% and egg numbers cyst−1 by 44.3–49.3%. The potato plants from P. fluorescens-ST and P. lilacinum-SD plots were 31.1–49.5% taller than untreated plants which also resulted in 27.2–32.0% higher tuber yield in P. fluorescens-ST and 25.9–30.2% in P. lilacinum-SD plots. The root colonisation of introduced P. fluorescens was 8.6–13.1 times higher in ST than SD. The trend was vice versa in P. lilacinum that colonised 3.1–3.6 times better in SD method than as ST. Their efficacy was comparable to carbofuran application. It is concluded that P. fluorescens-ST at 1 L t−1 of seed and P. lilacinum-SD at 5 L ha−1 are highly effective for management of PCN under naturally infested field conditions.

The field efficacy of Pseudomonas fluorescens, Purpureocillium lilacinum and Trichoderma viride liquid formulations was investigated against natural populations of root-knot nematode, Meloidogyne hapla. Two field experiments were conducted to test the effect of these biocontrol agents by seed treatment (ST) at 100 mL/kg of seed and by soil drenching (SD) at 5 L/ha. Their effect was compared with that of carbofuran 3G at 1 kg a.i. ha−1. Results showed that all the tested biocontrol agents were capable of reducing M. hapla juvenile (J2) population in soil, infection of female population in roots and egg numbers per gram of root at various levels. The biocontrol efficacy also varied according to the delivery method. The P. fluorescens-ST caused greatest reduction of J2 populations (67–69%) in soil, female infection (67–69%) in roots and egg numbers per gram of root (68–69%). Similar efficacy was observed in P. lilacinum-SD, which reduced J2 population by 64–67%, infection of female populations by 62–63% and egg numbers by 63–66%. The carrot plants treated with P. fluorescens-ST and P. lilacinum-SD were 33–36% taller with 28–36% more leaves and 27–30% longer leaves than untreated plants. It resulted in 20–21% higher root tuber yield in P. fluorescens-ST and 19% in P. lilacinum-SD plots. Root colonization of the introduced P. fluorescens was 6 times higher when it was applied as ST than as SD. The trend was opposite in P. lilacinum, which colonized 4–5 times higher in the SD method than as ST. The efficacy was comparable with that of carbofuran application. It is concluded that P. fluorescens-ST at 100 mL/kg of seed and P. lilacinum-SD at 5 L/ha are highly effective for the management of M. hapla, which infects carrot under field conditions.

The root-lesion nematode Pratylenchus penetrans is a major pathogen of potato worldwide. Yield losses may be exacerbated by interaction with the fungus Verticillium dahliae in the potato early dying disease complex. Accurate identification and quantification of P. penetrans prior to planting are essential for developing effective integrated pest control measures. However, distinction between P. penetrans and other Pratylenchus spp. based on morphology is a tedious task. A SYBR Green I-based qPCR assay was developed to discriminate, identify, and quantify P. penetrans in field soil. P. penetrans-specific qPCR primers were designed from the D2-D3 region of the 28S rDNA. The specificity of the assay was evaluated using eight isolates of P. penetrans populations and 31 isolates of other nematode species. A standard curve relating threshold cycle and log values of nematode number was generated from artificially infested soils. There was a high correlation between the P. penetrans numbers artificially added to soil or estimated from naturally infested field soils by conventional methods, and the numbers quantified using the qPCR assay. Grinding the field soil prior to DNA extraction improved P. penetrans detection from soil. The qPCR assay will not only be useful for differentiating P. penetrans from mixed populations of Pratylenchus spp., but also for efficient detection and quantification of P. penetrans from field soil. The assay requires no expertise in nematode taxonomy and morphology, and may serve as a useful diagnostic tool in research, diagnostic labs, and extension services for pest management.