Nematodes: Friends, Foes, or Both?

During field visits, I often come across people who ask – what exactly are nematodes? More often than not, many of them associate nematodes with everything bad that happens to their crops. Is this true? We’ll get into that too, but first, what exactly are nematodes?

Nematodes are invertebrate worms that have been around for about a billion years. Some of them are beneficial, while others are parasitic or neutral. They are typically vermiform or “worm-shaped,” but some species swell to become sphere-shaped in later life stages and do not resemble typical worms. Nematodes may also vary in size—some are 26 feet long and one inch wide, and some are tiny (250 um long and 15 um wide). A shovel of soil can contain millions of nematodes.

Nematodes are found everywhere on earth and can live inside animals, soil, plants, seeds, water, and everywhere else including human bodies. That’s right, humans can be affected by nematodes and in severe cases it can lead to serious health conditions. Mosquitoes, raw meat, contaminated food and water are a few modes of transmission, although the spread can be prevented with proper precautions. We will talk about that some other time, today the focus will be on plant nematodes.

Nematodes play a critical role in the soil and plant biology, and there are beneficial nematodes too that help improve the soil and the overall plant health. They feed on fungi, other harmful nematodes, bacteria, and protozoans, and can release nutrients for plant growth. Several “good” nematodes help control the insect population by attacking them. Many agricultural businesses rear and release them for that purpose.

I remember being happily surprised to learn that a group of researchers have used a specific nematode (Caenorhabditis elegans) to detect different types of cancer in human beings. They add a drop of urine to a dish containing Caenorhabditis elegans. If one of the fifteen types of cancer is present, the nematodes move toward the urine because they are attracted to certain compounds that the cancer cells produce.

Coming back to the plant parasitic nematodes, if let loose they can have a devastating impact on crops. The parasitic effects of nematodes have been discussed in Chinese literature as far back as 2700 B.C. It’s been estimated that plant parasitic nematodes cause more than 77 billion dollars of annual crop loss, ranking them among major agricultural pathogens worldwide.

Plant parasitic nematodes feast on all parts of the plants, especially roots, leading to various plant diseases and deformities. Nematodes that live mostly inside plant tissues are called “endoparasites,” while the ones that live in the soil are called “ectoparasites.” Some nematodes are capable of cryptobiosis, a sort of metabolic inactivity, during unfavorable conditions. They can stay dormant for years and then come back to life when favorable conditions present themselves. This survival mechanism makes it hard to eradicate bad or harmful nematodes.

Some of the ways to control plant parasitic nematodes include cultural, biological, and chemical methods. Depending on the situation, sometimes two or more of these control methods are employed to keep a check on nematode infestation.   

Cultural control could involve crop rotation with a non-host crop. Since many of the nematode species are not very mobile, equipment sanitation, rinsing tractors and tools before going from one field to another is also an effective way of cultural control.

Biological control uses pathogens of nematodes and natural predators. This control method can be expensive and not very effective under field conditions.

Chemical control is the most common method that’s been used for over fifty years. It can be expensive but has quick results. Fumigating soil with gas materials and non-fumigants in the form of liquid or solid is part of the chemical control of plant parasitic nematodes. The Environmental Protection Agency (EPA) has banned many of the fumigants due to environmental concerns. However, 1,3 dichloropropene (Telone II), chloropicrin (tear gas), dazomet (Basamid), sodium methyldithiocarbamate (vapam), and Potassium N‐methyldithiocarbamate (k-pam) can still be used. Non-fumigant products such as aldicarb, (Temik) and fenamiphos (Nemacur) can be used but are not as effective as current fumigants. Methyl bromide was the most effective soil fumigant used for years. However, its toll on the environment and the ozone layer caused it to be banned worldwide. It still may be used under strict guidelines and in rare circumstances in some parts of the world. These types of chemical control have shown to be short-term solutions and have adverse effects on soil, crops, and people in the long run. Some suggest keeping the molybdenum of soil at 3-5 ppm will help plants to be strong enough to fight nematode incursion.

So, what’s the alternative? Using natural products that have proven to be effective and safe for the people, environment, and plants is a practical and beneficial approach to control nematodes. Through laboratory and field studies, it has been shown that thyme oil-based nematicides are a safer and more effective way of reducing nematode pressure on farmlands. Speaking from my experience, Huma Gro^® Promax^® is an exceptional product that helps in diminishing nematode invasions in plants. It is an OMRI-listed, thyme oil-based biofungicide that has been tried and tested on multiple field trials and is currently being used by many farmers, growers and producers. It can be applied even up to the day of harvest. Generally, applying Promax^® (at 1 to 2 QT/acre) before planting and during the growing season has produced promising results against harmful nematodes. You can find detailed information and field trials on Promax^® here.

We will go into some more interesting details about nematodes in my next blog post, stay tuned.