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Nematodes: How They Help or Harm Your Soil

March 15, 2022

By Certis Biologicals

Nematodes are roundworms of the large phylum Nematoda, most of which are microscopic (less than 1 mm long) and invisible to the human eye. Nematodes are the most numerous multicellular animals on earth; a single teaspoon of soil may contain hundreds of nematodes of many species. While some nematodes are parasites of plants, insects, or vertebrates, many more species are free-living in soil where they help distribute beneficial bacteria and fungi through the soil and along the roots of plants by carrying microbes in their digestive systems and on their surface.

Awareness of their role in your soil will help you understand how nematodes may help or harm your crops and yield.

Beneficial Nematodes

Although the word “nematode” may stir fears of crop loss in the ag industry, not all nematodes are harmful!

Most nematode species occur as free-living organisms naturally in the soil and benefit soil health and the environment. They help break down organic matter (like a compost pile), and some species can also control above and below ground pests.

Some of these beneficial species are capable of infecting and killing insects, and are therefore known as “entomopathogenic” nematodes. Some strains of these beneficial nematodes have been produced at commercial scale for application to the soil, where they either actively hunt or lie in ambush for an insect host. After entering the host, usually through body openings, these nematodes release symbiotic bacteria that produce insecticidal toxins, killing the insect host within 24-48 hours. The nematodes then feed and reproduce within the host cadaver until their offspring move on to find a new host. When they move, they distribute beneficial bacteria and fungi through the soil.

Nematodes not only regulate pest organisms in the soil, they also mineralize nutrients into plant-available forms by releasing excess ammonium, act as a food source for other organisms, and act as biocontrol agents by consuming disease-causing organisms, depending on the type of nematode.

Beneficial nematodes may already exist in your soil, or you can purchase them and apply them through mixing them with water for ground cover.

Feeding Habits of Beneficial Nematodes:

Free living Nematodes:
  • Bacterivores
  • Fungivores
  • Omnivores
  • Predators
  • Entomopathogenic nematodes are those nematode parasites of insect pests.

Harmful Nematodes

Sorry we didn’t get the bad news out of the way, but there are some species called plant parasitic nematodes that are harmful to plants because they feed on the roots in the soil.

Harmful nematodes feed on root systems with a sharp needle-like structure called a stylet. The root knot nematode, Meloidogyne spp., is the most serious plant parasitic nematode problem in the world, because of its global distribution and wide range of host crops.

Many symptoms of nematode infestation can go unnoticed while still causing a negative impact on yield. Symptoms are often misdiagnosed as being caused by nutritional deficiencies or disease before growers ever know that is due to the nematodes present in the field and feeding on roots.

Root damage by nematodes reduces the plant’s ability to take up water and nutrients, weakening the plant and increasing its susceptibility to bacterial and fungal diseases and environmental stress. In the past, soil fumigants have been widely used to control harmful nematode populations, but most of these have been phased out due to hazards to beneficial organisms, humans, and the environment through off-gassing and soil leaching.

Temperatures and Other Environmental Factors

  • Root knot nematodes include a number of species parasitic to fruit and vegetables and row crops. Some examples below:
    • Meloidogyne (genus) and species include incognita, M. enterolobii, M. arenaria, M. javanica, M. hapla, and M. chitwoodi.
  • Sting nematodes:
    • Belonolaimus longicaudatus
  • Reniform nematodes
    • Rotylenchulus reniformis
  • Soybean cyst nematodes
    • Heterodera glycines
  • Lesion nematodes
    • Pratylenchus (genus) and several species occur like penetrans and P. brachyurus.


Fight Hidden Threats

Plant parasitic nematodes often linger in the soil, secretly causing root damage to crops before growers realize it.

Since it’s difficult to know if harmful nematodes exist in your soil, it’s important to take preventive measures to manage soil health and protect crop yield. A soil test can determine whether plant parasitic nematodes are present in potentially damaging numbers at time of sampling.

Plant parasitic nematodes are projected to cause an average global crop yield loss of over 10% annually, which corresponds to well over $100 billion dollars worldwide. If nematodes multiply and grow rampant in your soil, you face serious economic impact to your bottom line.

Don’t wait until it’s too late for your crops – take preventive measures to minimize yield losses due to plant parasitic nematodes.

When you need flexibility and convenience for every stage of growth, choose MeloCon® to manage harmful nematodes in organic production and conventional IPM programs.

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