Nematodes, known also as “the invisible pests”, are microscopic worms that live in the soil and feed plant roots, compromising their development.
This parasite affects so many types of plants, that they are one of the gardeners most feared enemies. In nature, there are numerous types of nematodes.
In this article, I want to stress the importance of them as pests, but not to be confused with beneficial nematodes, that although are parasitic worms as well, have the opposite effect on our garden and are a precious ally.
What is most alarming in the case that your crops suffer an infestation, is the fact that the damage is noticed only when it is already too late.
The most damaging nematodes are root-knot nematodes from the family of Meloidogyne Hapla. You can see the damage they do by observing the roots of your vegetables. These nematodes penetrate the roots in spring and they hide there until their entire life cycle is complete. Females develop inside the roots which swell to form the typical galls of infection. When young plants are attacked, numerous secondary roots are formed.
Nematodes are feared for two reasons: they suck the sap from our plant roots and they can become carriers of dangerous diseases for the plants. Once the root is pierced, this creates an opening for dangerous viruses to infest the plant. Nematodes, with their activity, favor the establishment of fungi and bacteria that cause root rot.
How To Identify Symptoms of Root Knot Nematodes In The Garden
These are the 6 main symptoms revealing how plants were attacked by root-knot nematodes:
- The presence of visible patches of underdeveloped vegetables in the rows of the garden
- The plants appear underdeveloped because the roots have a reduced the power of absorption of nutrients
- Very poor vegetable production, both from the qualitative and the quantitative point of view
- Greater susceptibility to the action of bacteria, fungi, and viruses.
- A poorly developed or malformed root system (galls and exaggerated secondary root formations)
- Yellowing of the leaves as well as leaves wilt, and even an early death.
Root-knot nematodes can affect more than 550 species of plants. Among the most common are: beans, cucumbers, carrots, lettuce, peas, green beans, celery, onions, leeks, cabbage, tomatoes, and radishes.
Nematodes can also affect the soil.
In the soil, the symptoms of nematode infestation is known as “sick soil syndrome”. Usually, by the time this condition is discovered, the nematodes have completely infested the soil.
This is a phenomenon that generally occurs where crops of the same species are planted year after year. Plants affected by nematodes release a toxin into the soil which over time leads to the developmental delay or even death of the plant itself.
Nematodes are widespread all over the world and have developed a strong resistance to adverse soil conditions over the millennia. For this reason, they easily overcome periods of intense cold or drought. These little worms are not very fast and don’t move around much, however they reproduce at very high speed. On the average, their life cycle is around 30 days, meaning that even a small infestation at the beginning of the growing season can rapidly increase and damage your crops in a short period of time.
How to get rid of nematodes from the soil – Organically!
The following measures are the best ways to get rid of root-knot nematodes naturally:
- Switch to winter crops.
- Avoid planting infected plants such as tubers or seeds
- Sterilize your tools and boots
- Soil Solarization
- Amend the soil with organic matter
- Use of green manure
- Water regularly
Let’s explain each subject in detail:
- Switch to winter crops: Plant winter crops instead of summer crops to take advantage of the period when nematodes are less active.
- Avoid planting infected plants such as tubers or seeds: The circulation and global trade of plants through the world network is the cause of the involuntary introduction of pathogenic organisms. Before planting your seeds or tubers, check that they come from a trusted supplier and that the product has passed the required checks.
- Sterilize your tools and boots: It is always a good idea to clean your tools properly and leave your shoes to dry in the sun after cleaning them so as not to be the carrier of pathogenic organisms from one place to another.
- Soil Solarization: this technique uses heat to kill nematodes, weeds, and other organisms. This method involves covering the soil with clear transparent plastic and taking advantage of the heat and the light coming from the sun. The trapped light heats the soil by reaching temperatures that would kill most living organisms.
- Tillage: The concept of tillage is to expose deeper layers of the soil to the sun in the hope to kill nematodes by desiccation. That’s because nematodes need dark and moisture to survive. This measure is only partially valid because many times tilling the soil does not reach those nematodes who are in deeper soil layers (they can dig deeper than 12 inches into the soil).
- Amend the soil with organic matter: Adding organic materials to the soil is a valued method of controlling parasitic nematodes and has led to increased production. The use of waste materials such as compost, livestock and poultry manure, and cellulosic waste seems promising to reduce nematode populations because it changes the structure of the soil which affects the pathogen development.
- Use of green manure: these are cover crops created to wither on a field so that they serve as a mulch and soil amendment. Some plants can be used as “bait plants” for nematodes, for example, plants like Arugula, Radish, black mustard, etc. These plants attract nematodes but once they will feed on them they won’t be able to reproduce.
- Biofumigation: This is an organic approach to kill soilborne pests. It involves the use of plants from the Brassicaceae family (like mustards, cauliflower, and broccoli) in rotation with cash crops. These plants have natural fungicidal and nematicidal properties and therefore are a valid alternative to chemical pesticides. The Brassicaceae are grown until flowering. Then they are mown and finely chopped, and reincorporated into the ground followed by heavy irrigation. The water activates the process which releases the bioactive principles that affect the nematodes.
- Water regularly: plants that are suffering from a lack of water are more susceptible to nematodes, therefore it is better to water regularly to strengthen the roots of the crops.
When are nematodes most active?
The period in which the nematodes are most active is in spring. During the winter, nematodes dwell in the soil in the form of larvae or eggs. As soon as the conditions become favorable, the humidity is optimal and the soil temperature reaches 64-68F (18-20 ° C), the eggs hatch, and the larvae penetrate the roots of the host plants. After 3 growing stages they reach maturity and lay their eggs. New larvae occur within 15 days and continue for as many as 6 life cycles a year. In mild temperature areas, the infestation begins around April and ends in November.
How To Prevent Root-Knot Nematodes
These are the measures to prevent root-knot nematodes from thriving in your soil:
- When planning your garden, choose a plant variety from the certified resistant to root-knot nematodes. Among these plants, you can find: broccoli, beets, Brussels sprouts, cabbage, collards, corn, English peas, garlic, mustard, onion, and potato
- Rotate Crops: In order to control nematodes, you need to plan ahead your crop schedule. Carry out crop rotations with resistant plants or with nematocidal plants (“bait plants” such as oil-bearing horseradish or white mustard, which attract parasitic nematode larvae but block their reproduction).
- Add cover crops (or green manures) to your soil such: marigold, rye, oat, and sorghum. The cover crops will provide organic matter and nutrients to the soil while reducing the root-knot nematode population.
- Strengthen the roots of perennial crops by applying a biological product with a fortifying action on the root system of plants, thus making them more resistant to attacks by nematodes and soil fungi.
- Be aware that this type of nematode prefers areas with a mild climate with sandy, light, and moist soil.
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