Nematodos: Qué Son y qué Enfermedades Causan en el Huerto

Today I will talk about nematodes, microscopic worms that can parasitize the roots of crops and cause diseases in the garden.

We have seen other times that two of the main problems in plants of the garden are the  pests and diseases. Pests are produced by insects, mollusks, birds, animals … (organisms that can be seen with the naked eye). In diseases , however, it is more difficult to detect the cause because they are produced by microorganisms : fungi , bacteria, viruses and, those that we will deal with today,  nematodes. 

What are nematodes ?: Pest or disease

Nematodes are a species of worms that live in water and in soil and that, when in very large concentrations, parasitize the roots  of plants, preventing the normal absorption of water and minerals.

They cannot move too much by themselves, so they are usually transmitted by irrigation water, contaminated substrates or by tools that have been in contact with affected areas (so be careful! Disinfect everything well if your plants have had diseases caused by nematodes) . The larvae enter the plants through the parts that are in contact with the soil (usually the absorbent hairs of the roots) and thus the disease is contracted.

As I have already mentioned, they are very small organisms that cannot be seen with the naked eye, although there are some species that can measure several centimeters, such as Anisakis (I suppose you will be familiar with this well-known parasite of some marine species that can also affect the people).

What crops do nematodes affect?

They mainly affect “root” crops such as potatoes, beets, carrots, turnips or onions; but they can also affect others such as lettuce, tomato or pepper.

Symptoms of nematodes

The nematodes begin to colonize the roots and the absorption of water and nutrients becomes difficult. This results in a decrease in plant growth , wilting, and yellowing of the leaves (until they finish drying out).

The clearest symptom of the presence of nematodes is nodules on the roots.  If you suspect that your plants’ disease has been caused by nematodes, remove them from the soil and observe the roots. If so, there will be a lot of spherical cysts of different colors and / or deformations (such as thickenings) along the length and width of the root.

You should not confuse these malignant nodules with the nodules that legumes have on the roots (these are good and serve to fix nitrogen and enrich the soil).

Prevent the presence of nematodes in the orchard

First of all, you should try not to infect your garden. Avoid recirculating irrigation water or that comes from stagnant places like lakes, and make sure that substrates and plants that come from seedlings that are not yours are not infected.

As with many garden problems, crop rotation  is a fairly effective preventive method. Especially when it comes to sensitive crops (tomato, potato, onion, beet …) avoid putting them two years in a row in the same place.

The contribution of organic matter through  natural fertilizers , such as compost , manure or green manures , helps control soil pathogens .  

Some flowers in the garden are  good to prevent nematodes , such as marigolds, the calendula, chamomile  or  brown mustard (Brassica juncea) as they  produce a root secretions that keep them away.

Ecological treatments to eliminate nematodes in the roots

If what you want is an ecological garden, as you know, you should not use chemicals or artificial insecticides to eliminate pests and diseases. If that is your case, I am going to give you now some ecological methods to eliminate nematodes.

The first thing you should know is that it is a very difficult microorganism to eradicate (since the eggs can remain dormant in the soil for years) so I recommend that you use preventive methods to avoid its appearance: Better safe than sorry “. 

Although not all will be eliminated, if you have had nematodes in an area of ​​the garden, try to leave it fallow the following year (especially in the spring-summer season) and remove the soil from time to time. Not having roots where to stay and being exposed to the sun (if you remove the earth you will take them outside) will reduce the populations to a minimum.

A very useful technique to eliminate a large part of the nematode population is to plant ‘trap plants’. It consists of planting crops that are susceptible to being attacked by nematodes ( Convulvulis, Crotalaria, Cyperus, Portulaca, Anaranthus … ), letting them grow until their development is complete and then, when the roots are infected with nematodes, quickly eliminate and destroy them.

I have read that there are some biological nematicides (which kill nematodes) allowed in organic farming, such as “Fornutri 10” or OMDV. Also the biological activator “Fire” is a phytofortifier that can help you to regenerate the soil.

Finally, two  quite effective soil disinfection methods : solarization and biofumigation .

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