Nematodes are microscopic roundworm- like organisms that live in water films and water-filled pore spaces within the soil. Nematodes have the ability to fill almost any part and body that contains at least some amount of water.
Most nematodes are free-living organisms which feed on bacteria, fungi, protozoans, or other nematodes. Many are parasites of animals and plants. Although nematodes are tiny organisms, they can be significantly harmful to plants and create headaches for farmers.
Damage Caused from Nematodes Feeding on Plants
Nematodes feed on all parts of the plant, including roots, stems, leaves, flowers, and seeds. Depending on the plant part they feed on, nematodes are grouped into:
- Migratory endoparasites
- Sedentary endoparasites
- Stem and bulb nematodes
- Seed gall nematodes
- Foliar nematodes.
Not only do they differ in the plant tissue they attack, nematodes also cause varying symptoms to plant tissue. Some species withdraw the plant cell content, thus creating large lesions in the plant tissue eventually killing the plant. Some make deformations on plant tissue by ‘’tricking’’ the plant cells to enlarge and grow, thus creating more cells for nematode feeding.
Many plant-parasitic nematodes feed on the plant roots. Their feeding damages the plant's root system in the following ways:
- Reduced root mass
- Distortion of root structure
- Enlargement of the roots
- Reduced ability of the plant to absorb water and nutrients
- Increased plant susceptibility to other plant pathogens.
Nematodes feeding on plant shoots can cause visible signs on the plant, such as:
- Reduced plant vigor
- Distortion of plant parts
- Death and infected plant tissue
- Stunting growth
- Poor yield.
How to Recognize a Nematode Infestation in the Field?
Nematode feeding damage is not easy to recognize since symptoms are similar to the attack of some disease pathogens. Additionally, if a nematode infects plant roots, symptoms on the plant are not usually visible until the infestation has become severe. At this point it is usually too late to protect the crops, the damage has been done.
The only way to accurately confirm nematode presence is to sample the soil and plant material from suspected sites and extract nematodes for analysis. Nematodes can be extracted from the soil by submerging in water to remove the heavy soil particles and then catching the floating nematodes on sieves with fine pore sizes. Additionally, nematode presence in plant tissue can be analyzed by incubation in a Baermann funnel or moist chambers. Nematodes, if present, can be collected while exiting the tissues.
Nematodes are not very mobile in the soil; only moving up to one meter through the soil within their lifetime. However, they can be easily spread through the field in additional ways:
- Using farm equipment contaminated with nematode-infested soil
- During or due to a flood or during irrigation, which can spread nematodes over long distances
- Transporting of nematode infected plants, seeds, and bulbs which can spread nematodes internationally.
Nematode control is a complex and long-lasting process which combines various cultural, biological, and chemical measures. Care should be taken to practice preventative measures before the nematode population increases and infests the entire field.
Control measures efficient in nematode prevention are:
- Crop rotation – growing of non-susceptible crops
- Fallowing- leaving the soil empty for a certain period of time
- Soil solarization – high temperatures decrease nematode population in the soil
- Sanitation- planting of nematode-free plants, regular cleaning of farm equipment
- Planting of nematode-resistant plants
- Planting at lower temperatures to avoid nematode damage
- Use of natural predators of nematodes
- Soil fumigants (gas) and non-fumigants (liquid or solid)- restricted use due to the toxic effect on the environment.
Nematodes are plant pests that are widely distributed from temperate to tropic climate regions. Many farmers are unaware of the hazardous effects of nematode infestation. However, the fact remains that nematodes within an affected area can seriously impact crop production and even make future farming impossible.
Which protection measure to use to control nematodes depends on climate, soil type, crop type, severity of infestation, and nematode type. The farmer’s knowledge and financial ability to implement control practices has the potential to make all the difference.