Understanding the Threat: Why Nematodes Are a Serious Problem for Your Crops

Plant-parasitic nematodes are among the most damaging yet often underestimated threats to agricultural productivity. These microscopic worms reside in the soil or invade plant roots and stems, silently impairing nutrient absorption, weakening plant structure, and drastically reducing yields. Once established in a field, they are difficult to eradicate without a targeted and informed approach.

There are many different types of nematodes, each with specific host preferences and symptoms. Among the most destructive are root-knot nematodes (Meloidogyne spp.), which form galls or “knots” on roots and can devastate crops like tomatoes, cucumbers, and carrots. Lesion nematodes (Pratylenchus spp.), on the other hand, cause root necrosis and are notorious for infecting wheat, corn, and potatoes. Cyst nematodes (Heterodera spp.), including the soybean and sugar beet varieties, severely hinder root function and plant development.

Whether you’re managing an open field, a greenhouse operation, or high-value specialty crops, recognizing early signs of nematode infection—such as poor plant growth, stunting, chlorosis, or wilting despite adequate water—is critical. The damage may appear subtle at first but can escalate quickly if left untreated, making nematicide intervention not just advisable, but essential.

In this guide, we’ll help you choose the right chemical or biological nematicide based on nematode type, crop species, and field conditions. From fumigant soil treatments to systemic root protectants, we’ll break down the available options so you can design a proactive and effective nematode management strategy.

Common Types of Plant-Parasitic Nematodes and Their Host Crops

Understanding which nematode species are affecting your crops is the first step in selecting the most suitable control solution. Below are six of the most economically important nematode pests found in agricultural systems, along with their damage characteristics and typical host crops.

1. Root-Knot Nematodes (Meloidogyne spp.)

These are among the most widespread and destructive nematodes. They invade plant roots, forming characteristic root galls that severely disrupt water and nutrient uptake. Infected plants often show signs of stunting, chlorosis, and reduced yields.

• Typical Symptoms: Swollen galls on roots, yellowing leaves, stunted growth
• Major Host Crops: Tomato, cucumber, eggplant, carrot, tobacco, soybean
• Damage Level: High; especially in protected cultivation and vegetable production

2. Stem Nematodes (Ditylenchus spp.)

Stem nematodes attack above-ground plant tissues, including stems, bulbs, buds, and floral parts. Their activity causes swelling, deformation, and tissue decay, making them particularly troublesome in bulbs and floriculture crops.

• Typical Symptoms: Stem swelling, tissue rot, malformed buds or leaves
• Major Host Crops: Garlic, onion, potato, chrysanthemum, strawberry
• Damage Level: High in horticultural and flower crops

3. Lesion Nematodes (Pratylenchus spp.)

Also called root-lesion nematodes, they migrate within the root cortex, creating necrotic lesions that predispose plants to secondary fungal infections. These are often difficult to detect until crop performance declines sharply.

• Typical Symptoms: Black root lesions, root decay, poor nutrient uptake
• Major Host Crops: Corn, wheat, soybean, potato, sugarcane
• Damage Level: Moderate to severe in row crops and cereals

4. Cyst Nematodes (Heterodera spp.)

Cyst nematodes cause severe root disruption through the formation of cyst-like egg sacs. They are highly host-specific and remain viable in soil for years, making rotation and control particularly challenging.

• Typical Symptoms: Yellowing, wilting, poor plant development
• Major Host Crops: Soybean (H. glycines), sugar beet (H. schachtii), oilseed rape
• Damage Level: Very high in monoculture systems

5. Spiral Nematodes (Helicotylenchus spp.)

These nematodes reside on the root surface and interfere with root development, limiting the plant’s ability to absorb nutrients. Though typically less aggressive, their presence often exacerbates the effects of other soil-borne pathogens.

• Typical Symptoms: Underdeveloped roots, uneven growth
• Major Host Crops: Found in a wide range of vegetable and ornamental crops
• Damage Level: Low to moderate; often a secondary stress factor

6. Sting Nematodes (Belonolaimus spp.)

Sting nematodes attack the root tips, halting root elongation and resulting in stubby, inefficient root systems. They are particularly problematic in sandy soils and high-value crops like turfgrass and tobacco.

• Typical Symptoms: Root tip dieback, stunted seedlings, patchy field growth
• Major Host Crops: Turfgrass, peanut, cotton, tobacco
• Damage Level: High in sandy or light-textured soils

Types of Nematicides: Choosing the Right Mode of Action for Maximum Control

Nematicides are divided into two broad categories based on their formulation and mode of action: chemical nematicides and biological nematicides. Understanding the advantages, limitations, and ideal application scenarios of each type is essential for designing an effective nematode control strategy tailored to your crops, soil conditions, and operational goals.

1. Chemical Nematicides

These products are formulated with synthetic active ingredients designed to kill or suppress nematodes through direct toxicity. They are fast-acting and suitable for high-pressure situations but must be handled with strict safety and environmental precautions.

A. Fumigant Nematicides (Soil Disinfestation Agents)

Fumigant nematicides volatilize in soil and spread through vapor action, sterilizing the root zone by penetrating nematode-infested areas. These are applied before planting and require soil sealing or moisture management to be effective.

• Best Use Case: Pre-plant soil disinfestation for vegetables, greenhouses, and high-value crops
• Formulation Forms: Liquid concentrate (SL), granular (GR), or gas injection
• Target: Broad-spectrum soil pests including nematodes, fungi, insects, and weed seeds
• Caution: Restricted use in many regions due to volatility and safety concerns

B. Non-Fumigant Nematicides (Contact or Systemic)

These are applied during the crop cycle as soil drenches, granules, or foliar applications. They can act via contact toxicity or systemic translocation to the root system, providing protection to growing plants.

• Best Use Case: Season-long root zone protection or hotspot treatment
• Formulation Forms: CS (capsule suspension), GR (granule), SC (suspension concentrate), EW (emulsion), ME (microemulsion)
• Target: Specific nematodes attacking active crop roots
• Advantages: Less hazardous than fumigants; compatible with IPM programs

2. Biological Nematicides

Biological nematicides use naturally occurring microorganisms or plant-derived compounds to suppress nematodes. They offer a safer and often environmentally sustainable alternative to chemical control, especially for integrated and organic farming systems.

A. Fungal-Based Nematicides

These products contain spores of beneficial fungi that parasitize nematode eggs or colonize root zones to prevent nematode invasion. They are slow-acting but highly compatible with biological soil health management.

• Key Advantages: Residual soil effect, improved root resilience, non-toxic to beneficial insects
• Ideal Use: Nursery crops, organic farms, or continuous use in IPM programs

B. Bacterial-Based Nematicides

Formulated from nematode-antagonistic bacteria, these products inhibit nematode reproduction or release toxins into the rhizosphere. They are typically applied as soil drenches or seed treatments.

• Target Action: Interruption of nematode life cycle stages, especially juveniles and eggs
• Use Case: Soil amendment or combination with organic fertilization programs

C. Plant-Derived Nematicides

Natural alkaloids like matrine are extracted from botanical sources and provide contact or repellent effects. These are often used in low-residue farming or protected cultivation settings.

• Advantages: Biodegradable, low risk to mammals, minimal residue
• Use Form: Typically liquid SL (soluble concentrate) for foliar or soil application

Recommended Nematicide Active Ingredients for Broadacre and Specialty Crops

Choosing the right nematicide depends not only on the target nematode species, but also on the crop type, application method, and safety profile. Below is a detailed breakdown of recommended active ingredients for broadacre crops first, followed by horticultural and high-value crops, categorized by their formulation type and biological or chemical origin.

Chemical Nematicides for Broadacre Crops

These options are widely used in large-scale farming systems to suppress high nematode pressure in crops like soybean, corn, wheat, sugarcane, potato, and cotton.

1. Fosthiazate (Non-Fumigant, Contact & Systemic Action)

• Formulations: 10% GR (granule), 30% CS (capsule suspension)
• Mode of Action: Inhibits acetylcholinesterase in nematodes, leading to paralysis and death
• Application: Soil application at planting or as early topdressing
• Use Case: Highly effective for root-knot nematodes, lesion nematodes, and cyst nematodes in corn, soybean, and sugarcane
• Advantages: Quick knockdown, long-lasting soil activity, compatible with mechanized granule application

2. Fluopyram (Systemic, Preventive and Curative)

• Formulations: 40% SC (suspension concentrate)
• Mode of Action: Inhibits mitochondrial respiration in nematodes, stopping feeding and reproduction
• Application: Soil drench, in-furrow, or seedling root dip
• Use Case: Effective against root-knot, lesion, and spiral nematodes in soybean, wheat, potato
• Advantages: Dual action against nematodes and some fungal diseases (e.g. Rhizoctonia); useful in IPM programs

5. Multi-Active Granule Formulations

• Example Combination: Fosthiazate 3% + Abamectin 0.5% + Fluopyram 0.5% GR
• Application: Pre-plant granule broadcasting or band placement
• Use Case: Designed for severe nematode infestation in potato, peanut, sugarcane, or soybean rotations
• Advantages: Multiple modes of action reduce resistance risk; broad-spectrum nematicidal coverage

Chemical Nematicides for Vegetables, Fruits & Specialty Crops

These formulations are more targeted and often used in greenhouses, orchards, and high-value vegetable systems (e.g., tomato, cucumber, tobacco, carrot).

1. Chloropicrin (Fumigant, Pre-Plant)

• Formulation: 99.5% SL
• Use Case: Soil sterilization before planting vegetables
• Target: All nematode types
• Caution: Requires soil sealing and regulated handling

2. Dazomet (Fumigant Granule)

• Formulation: 98% GR
• Use Case: Soil disinfestation in nursery beds and protected cultivation
• Advantages: Controls nematodes, weeds, and fungal pathogens simultaneously

3. Sulfuryl Fluoride (Gas Fumigant)

• Formulation: 99%
• Use Case: Postharvest and storage area sanitation, not for field soil
• Target: Used primarily to eliminate hidden nematodes in planting media or bulbs

Biological Nematicides: Sustainable Control for Safe, Long-Term Use

With increasing demand for residue-free produce, soil health, and sustainable farming, biological nematicides are gaining popularity. These bio-based products harness the power of naturally occurring fungi, bacteria, and plant extracts to suppress nematode populations while promoting root vigor and microbial diversity.

They are especially well-suited for:

• Organic farming systems
• Vegetable nurseries and seedbeds
• Greenhouse operations
• Export-focused horticulture
• Fields with long-term soil fertility goals

Below are the three main types of biological nematicides and their recommended actives:

1. Fungal-Based Nematicides

Purpureocillium lilacinum (formerly Paecilomyces lilacinus)

• Formulation: 500 million viable spores/g GR
• Mode of Action: Parasitizes nematode eggs and juvenile stages; colonizes rhizosphere for lasting protection
• Use Case: Effective against root-knot nematodes in tomato, cucumber, tobacco, banana, and eggplant
• Advantages: Promotes plant growth, compatible with most soil types, excellent for greenhouse IPM

Verticillium chlamydosporium

• Formulation: 250 million spores/g GR
• Mode of Action: Attacks cyst and egg stages, particularly effective in cyst nematode hotspots
• Use Case: Ideal for sugar beet, canola, and soybean fields with confirmed cyst nematode infestations
• Advantages: Target-specific, reduces cyst population without harming non-target organisms

2. Bacterial-Based Nematicides

Bacillus thuringiensis (Bt) – Soil Strains

• Formulation: 16000 IU/mg WP
• Mode of Action: Produces toxins that inhibit nematode feeding and development
• Use Case: Useful in seedbed protection, seed coating, or transplant soaking for crops like lettuce, leafy greens, and melon
• Advantages: Broad-spectrum bio-insecticidal and bio-nematicidal activity, low resistance risk

3. Plant-Derived Nematicides

Matrine (from Sophora root)

• Formulation: 0.6% SL
• Mode of Action: Natural alkaloid disrupts nematode nervous system and reproduction
• Use Case: Commonly applied as root zone spray or soil drench in cucumber, strawberry, and Chinese herbs
• Advantages: Fast degradation, low environmental impact, safe for pollinators and beneficial soil fauna

When to Choose Biological Over Chemical Options

Product Selection Guide for Nematode Control

Nematode control needs vary among crops and growing environments, and the following are recommended programs for major crop types:

A. Field Crops (Soybean, Corn, Wheat, Potato, Sugarcane)

Frequently Asked Questions (FAQ)

Q1: Can nematicides be mixed with fertilizers or insecticides?

A: Some systemic non-fumigant nematicides (e.g., Fluopyram, Abamectin) can be tank-mixed with compatible fertilizers or insecticides. Always check the label or consult your supplier for compatibility and pH tolerance.

Q2: When is the best time to apply nematicides?

A:

• Fumigants: Before planting during land preparation.
• Non-fumigants: At seedling stage or early root development.
• Biologicals: Apply early and repeat during root flush for best root colonization.

Q3: How long do nematicides remain effective in the soil?

A:

• Fumigants: 3–6 weeks (residual sterilization effect).
• Non-fumigants: 2–4 weeks, depending on formulation.
• Biologicals: May persist longer if soil conditions favor microbial survival.

Q4: Are there any residues or safety concerns?

A:

• Modern nematicides like Fluopyram and Abamectin have favorable residue profiles when used as directed.
• Biologicals such as Purpureocillium lilacinum and Matrine are residue-free and ideal for export-sensitive crops.