Nematodes are a type of roundworm, with over 25,000 species being found. Over half of that total has been found to be parasitic, and they also have a tubular digestive system, meaning that there are openings on both ends of the animal. They have adapted to almost every ecosystem on the Earth, and are found in every part of the lithosphere.
Plant-parasitic nematodes have the potential to cause severe crop loss. Some species even cause damage to the roots, including the formation of visible galls. These are caused by root-knot nematodes, and the knots are helpful for identifying the pests in the field. Some of the nematode species also transmit plant viruses by feeding on the roots. These species transmit grapevine fan-leaf virus, as well as arabis mosaic virus.
The Golden Nematode is one species that has become notorious for causing harm that has resulted in quarantines and crop failures across the globe. Interestingly enough, plots that have Indian mustard green manure or seed meal in the soil have found a 13 to 14-fold reduction in the nematode population.
How to Identify Nematodes
Nematodes exist basically everywhere, and there are beneficial species as well as harmful species. Some signs that you have an infestation of plant-parasitic nematodes are: unexplained wilting, general plant decline, stunting, off color, early maturing small fruit, root systems with lesions and distortion, root nodules, and distortion above soil parts.
If a lawn has an infestation, the signs usually show up early, and if an infestation occurs in a plant, it may take longer for signs to develop. Really the only way to determine that there is an infestation of plant-parasitic nematodes is to collect a soil sample for a population count which will in turn determine the species present as well as a population count. For each species there is a population range from acceptable to excessive and this will be what the sample is compared to.
How to Control Nematodes
Marigolds that are grown over one or more seasons can control nematodes, as the effect is cumulative. Plants can also be treated with the fungus called Gliocladium roseum, or with a natural biocontrol called Chitosan. The Chitosan evokes a plant’s defense response to destroy the parasitic nematodes on roots of plants like corn, potatoes, tomatoes, soybeans, and sugar beets, all while not harming the beneficial nematodes that live in the soil.
It is also possible to do soil steaming prior to planting a crop, but this method kills both the parasitic and beneficial soil fauna. There are no chemicals that are specifically nematicides that are effective in eradicating the population of a plant-parasitic nematode infestation.
Organic amendments may be added to soil as compost, regular manure, and green manure. This organic matter can help prevent the damage of nematodes in several ways. It increases the ability of the soil to hold water and nutrients, while improving the soil structure. This means that the environment for the plants is improved, and can help the plants survive in spite of the nematodes. These organic amendments also increase the natural enemies of the nematodes that suppress the population, as well as sometimes release gasses or chemicals that are toxic to the plant-parasitic nematodes.
Biopesticides such as MeloCon WG contain a fungus that parasitizes the eggs of nematodes. This product will suppress but not totally eliminate a few species of nematodes such as root-knot and sting. This should be applied multiple times and continue to be applied through the growing season. Additionally, it will not be effective for treating established plants that have damaged caused by nematodes.
Tips for Treating
Nematode activity slows down when the soil temperature drops. This means that plants that grow in the cooler months do not suffer from nematodes as much as those that grow in the warmer months.
Inspect the roots of all plants used for landscaping before purchasing, look for root-knot galls and any other root related problems that are caused by nematodes. This is just another way that nematodes are introduced.
Sometimes in a garden that is planted with annuals, it is possible to replace the soil and completely start over. There is a chance that the nematodes will infest again, but at that point the plants will have an established root system that will tolerate an infestation. The benefit of replacing the soil may only last one or two seasons.