Apart from pests, fungi and viruses that affect crops we also have to pay attention to nematodes. They are commonly referred to as small worms, of about 0.2 mm, and are usually unknown by many farmers, blaming some problems caused by these organisms to other types of diseases or pests; although there are also beneficial ones.
Not everyone knows what or what a nematode represents in agriculture.
They can distinguish between plants and diseases (fungi, bacteria, viruses, etc.) but they do not classify nematodes.
It occurs to me that it is a normal situation, since it is a type of living being that cannot be seen , that it affects crops in a confusing way (it is often confused with other physiological problems) and because its treatment is usually be complicated.
WHAT EXACTLY ARE NEMATODES?
They are within the Animalia kingdom and are considered as vermes (worms).
In addition, they are classified as pseudocoelomatas , which in order not to complicate us much we could say that it is a way to distinguish different mobile forms of worms.
This world of nematodes is terribly difficult to explain and catalog …
Although there are many aquatic organisms of this kind, those that affect our crops are usually terrestrial.
Many of them, as we will see in the list of nematodes, are parasites of plants and even animals (including us, humans).
Within the nematodes that attack plants we can differentiate them as follows:
- Endoparasites: they are found inside the plant, they even develop their eggs inside. This is the case of Meloidogyne .
- Semi-endoparasites: as the same word says, a part of this worm gets inside the plant and another remains outside. For this reason, the laying is done outside the plant. They are semi-endoparasites Heterodera , Globodera and Pratylenchus.
- Sedentary ectoparasites: we go from the inside out. In this case, the ectoparasites only introduce the head inside the plant, shedding only when they reproduce. This is the case of Paratylenchus and Ratylenchus.
- Migrating ectoparasites: they only bite the plant through the stylet. Some examples of these organisms? Xiphinema and Trichodorus .
HOW DO THEY ATTACK PLANTS?
Most of the time, they are on the ground. Therefore, its attack is carried out exclusively on the roots.
This is a problem for the farmer, as he cannot predict or avoid the attack until he already notices a problem in the crop (almost like the red palm weevil).
SYMPTOMS ON CROPS
In most cases, the following symptoms appear:
- Delayed sprouting.
- Widespread weakening or lack of growth.
- Lack of root development (not noticeable by the farmer).
HOW DO YOU FIGHT NEMATODES?
Treatment for these types of worms is tremendously complicated. Although it varies according to the type of species and its classification (which we have seen previously), those that carry out their life cycle inside the plant are difficult to eliminate.
In fact, there are many products that are classified as nematostatics . They are those that allow the development of the crop taking into account that it will always be affected by these organisms.
In the market for products to treat these tiny animals, we can distribute them between those of an ecological type and those of an integral type.
There are some active substances that work as nematicides, although many of them are only applicable when the earth is bare. That is, to disinfect the soil (such as solarization , a natural disinfection system available to everyone).
Oxamyl (check its authorization) is a useful active ingredient against certain types.
It is incorporated by drip irrigation and has a certain systemic action on both roots and leaves. You can also check other authorized products against nematodes here .
Some fungal spores are used as an ecological treatment to control this pest.
This is the case of Paecilomyces lilacinus, which acts on them in all physiological states.
Sodium hypochlorite (the bleach of all life) is also used as a soil disinfectant, even when there are cultivated plants.
You only have to pay special attention to the recommended amounts (doses of 1L / 1000 m2), since drip applications can generate phytotoxicities.
LIST OF PHYTOPATHOGENIC NEMATODES
NEMATODE APHELENCHOIDES FRAGARIAE ( RITZEMA BOS) CHRISTIE
NEMATODO APHELENCHOIDES RITZEMABOSI (SCHWARTZ) STEINER AND BUHRER
NEMATODO DITYLENCHUS DIPSACI (KHÜN) FILIPJEV
NEMATODE GLOBODERA PALLIDA ( STONE) BEHRNS
NEMATODO GLOBODERA ROSTOCHIENSIS (WOLLENWEBER) BEHRNS
NEMATODO GLOBODERA TABACUM COMPLEX STONE
NEMATODE HETERODERA AVENAE WOLLENWEBER
NEMATODE HETERODERA CRUCIFERAE FRANKLIN
NEMATODE HETERODERA CYPERI GOLDEN, RAU, COBB
NEMATODE HETERODERA CIFI KIRJANOVA
NEMATODO HETERODERA FILIPJEVI ( MADZHIDOV) STONE
NEMATODO HETERODERA GOETTINGIANA LIEBSCHER
NEMATODO HETERODERA HUMULI FILIPJEV
NEMATODE HETERODERA LATIPONS FRANKLIN
NEMATODE HETERODERA MEDITERRANEA VOVLAS, INSERRA AND STONE
NEMATODE HETERODERA SCHACHTII SCHMIDT
NEMATODE HETERODERA TRIFOLLI GOFFART
NEMATODES LONGIDORUS REDUCED HOOPER;
NEMATODE LONGIDORUS ELONGATUS ( DE MAN) THORNE AND SWANGER
NEMATODE LONGIDORUS MACROSOMA HOOPER
NEMATODO MELOIDOGYNE ARENARIA (NEAL) CHITWOOD
NEMATODE MELOIDOGYNE ARTIELLA FRANKLING
NEMATODE MELOIDOGYNE BAETICA CASTILLO, VOVLAS, SUBBOTIN AND TROCOLI
NEMATODE MELOIDOGYNE HAPLA CHITWOOD
NEMATODE MELOIDOGYNE HISPANICA HIRSCHMANN
NEMATODO MELOIDOGYNE INCOGNITA (KOFOID AND WHITE) CHITWOOD
NEMATODO MELOIDOGYNE JAVANICA (TREUB.) CHITWOOD
NEMATODE PARATRICHODORUS MINOR (COLBURN) SIDDIQI
NEMATODE PARATRICHODORUS PACHYDERMUS (SEINHORST) SIDDQI
NEMATODE PARATRICHODORUS TERES (SEINHORST) SIDDIQI
NEMATODE PRATYLENCHUS COFFEAE ZIMMERMAN
Guests: coffee, banana and citrus.
Symptoms: they cause lesions in the roots, of which they are endoparasites. The roots acquire a characteristic dark brown color due to the necrosis of the affected cells.
NEMATODE PRATYLENCHUS VULNUS ALLEN AND JENSEN
NEMATODE TRICHODORUS CYLINDRICUS HOOPER
NEMATODE TYLENCHULUS SEMIPENETRANS COBB
NEMATODE XIPHINEMA DIVERSICAUDATUM (MICOLETZKY) THORNE
NEMATODE ZYGOTYLENCHUS GUEVARAI ( TOBAR) BRAUN & LOOF
EYE! NOT ALL NEMATODES ARE HARMFUL TO OUR CROPS
Until now, we have only talked about how problematic plant pathogenic nematodes can be, but as in any group of organisms, there are harmful and beneficial ones. Now it’s time to talk about the latter to leave us a good taste in the mouth (perhaps not the most accurate expression ..).
We are talking about entomopathogenic nematodes , those that necessarily parasitize insects.
This is where etymology helps us memorize the terms:
- Phytopathogens: Phyto comes from the Greek and means plant. Pathogen in turn comes from pathos (disease) gen- (produce, beget).
- Entomopathogenic: Entomo comes from the Greek and means insect.
You can imagine where the shots go, right? They can help us control pests.
It is not that they are a panacea but there are promising studies in this regard and some of them have proven efficacy against certain pests.
They are what is included within the bioinsecticides for the biological control of pests.
HOW DO ENTOMOPATHOGENIC NEMATODES ACT?
As we have just mentioned, these nematodes are obligatory hosts for insects. But it is not the nematode that kills the insect.
It is all much more complex and worthy of a Machiavellian plan. This is what is known as nematode-bacteria symbiosis . Let’s say that the nematode is the vector of the bacteria that infects the insect’s organism.
[alert style = »red»] A biological vector is any living being that serves as a transport and transmits an infectious agent to another organism. [/ alert]
NEMATODE LIFE CYCLE AND METHOD OF INFECTION (SIMPLIFIED)
The nematode enters the interior of the insect through its natural ways, such as with the mouth and anus mainly.
Once inside, it reaches the digestive system and pierces certain membranes inside the digestive tract by mechanical action (such as those that attack plants) and by enzymes . When the nematode has entered the insect’s hemolymphatic system, it releases the bacteria.
All this process occurs in a few hours and even without reaching the time from the infection.
That’s when the bacteria that have accessed the hemolymph end up killing the insect with septicemia in a day or two.
And the nematode? What about him?
Well, since it is a symbiosis, by definition, it has to have a benefit like the bacteria and that is that it feeds on it (which has reproduced throughout the interior of the insect), it completes the last stage becoming nematodes with capacity reproductive (either dioecious or hermaphroditic).
In the end, a second generation of adults is generated and so on until the food resources that are the corpse itself are scarce.
At that time of scarcity is when the nematodes go to the infective stage, they leave the insect (or what is left of it) in search of a new host.
All this happens in hours and in exponential production.
Seeing this, it can be scary because the first thing that comes to mind is if they are safe for us since after all these sophisticated insect killing machines are in the crops we feed on.
They have no problem and are totally safe for man, plants and even other animals. They are very selective about the insects they attack.
That is why they are so interesting, because of their high specificity.
HOW ARE ENTOMOPATHOGENIC NEMATODES APPLIED?
Like Bacillus thuringiensis , being a microscopic organism, it can be applied with traditional sprayers, whether they are manual or tractor-mounted backpacks, injectors and even irrigation water.
They are also compatible with many chemical pesticides and can be supplemented and thus lower the dose of the first. We must take into account two advantages over a chemical pesticide:
- The chemical pesticide starts from an initial dose that is depleted with time and action. In the case of the nematode, the action will be just the opposite. From the first application, as long as there are insects, the nematode population will increase exponentially.
- The pesticide will act on contact; However, the nematode is a living organism, with mobility that in its infective state looks for its victim, being able to access areas where the chemical does not reach in the application.
It also has some downsides . Being living organisms, they have “comfort” ranges of development and outside of them their effectiveness is reduced for biologically obvious reasons.
Its optimal development and therefore its effectiveness depends on:
- Degree of invasion
- Establishment of the nematode and multiplication of the bacteria
- Persistence in the middle
- Resistance to the host’s immune system.
- Resistance to environmental conditions (temperature, pH, humidity and composition of the soil).
TWO FAMILIES OF ENTOMOPATHOGENIC NEMATODES: STEINERNEMATIDE AND HETERORHABDITIDAE
It is the most studied of all entomopathogens. It attacks lepidopteran larvae mainly.
STEINERNEMA GLASERI NEMATODE
It mainly attacks beetle larvae. The infective forms are very mobile and are suitable for parasitizing insects with reduced mobility.
NEMATODE STEINERNEMA SCAPTERISCI
This nematode is highly specific as it is effective against crickets.
NEMATODE STEINERNEMA FELTIAE
It mainly attacks Diptera larvae and can withstand very low temperatures in the soil.
NEMATODE STEINERNEMA RIOBRAVIS
It is less specific (broader spectrum) and attacks several orders of insects. It is characterized by being adapted to high soil temperatures and dry conditions.
NEMATODE HETERORHABDITIS BACTERIOPHORA
It is also broad-spectrum and attacks various larvae of Lepidoptera, Coleoptera, and other insects. It is very effective against root weevils. It is adapted to warm soil temperatures. Another species with similar characteristics is Heterorhabditis megidis.
There are many more species and we will talk at length about more than particular cases of entomopathogenic nematodes.
WHAT PRODUCTS KILL AND WHICH ARE (SIMPLE) REPELLANTS?
Currently there is chaos in the matter of the registration and sale of phytosanitary products, phytofortifiers and others.
Even some certified organic products cause serious problems related to health alerts due to phosphonate content and other compounds that contribute to soil and plant contamination.
And all this, with the subject of nematodes , there is also a lot to say.
Paper holds everything and many times we find a large number of products that claim to act against nematodes when in reality what they do is stimulate root development.
This for an inexperienced farmer may be worth it, since their eyes see how the plant seems to start to grow and leave the cumbersome past in which its roots were being “eaten” by these little bugs known as nematodes.
Now, if we could control what happens from the stem down, things would change a lot.
In this case, a product that acts by stimulating root development would practically be giving the nematodes more food .
The growth of the plant would be noticeable, but if the nematode population continues to grow (due to easy availability of food and good temperature and humidity in the soil), the plant will undergo a new biotic stress (caused by organisms) and will be again subjected to the yoke of this difficult plague.
CONCLUSION NUMBER 1: NEMATODE PRODUCTS ARE EXPENSIVE
A large nematode infection in a soil is a real headache . If you really want to continue growing and get a more or less appropriate harvest, you have to stop the advance of this pest.
Perhaps for winter crops it is less noticeable, since soil conditions are quite cold and irrigation is reduced to a minimum. In short, the conditions for the development of the nematode population are not ideal.
However, when the heat arrives little by little, the risks increase and the temperature of the soil begins to rise, the nematodes prepare for the attack , the eggs begin to hatch and any roots installed in the soil become a feast for them. little bugs.
The farmer, with fear in his body, decides to buy a product to combat nematodes , from which, the game of product marketing together with the desperation to save the crop makes the monetary outlay greater and we take products that then they don’t do what we think they will do.
NEMATICIDE = REDUCE NEMATODE POPULATION
It is necessary to clarify the difference between different terms related to the world of nematodes.
- Nematicide: a product from which, from the moment of its application, the population of nematodes in the soil is reduced.
- Repellent: a product that does not reduce the nematode population, but it does manage to avoid direct contact, for a limited time, between the pest and the root.
- Nemato-static: a solution that keeps the evolution of nematodes at bay, which maintain a stable population over time. It does not grow, but it does not go down either.
- Phytofortifying: a product based on stimulating the development of the roots to favor the growth of the plant, without actually acting on the nematode population.
WHICH IS THE BEST?
From our point of view, the combined action of the first and the last. Of course, as long as money allows it.
There will be no better response on the plant than the union of reducing the nematode population and stimulating root development.
HOW DO I KNOW IF A PRODUCT KILLS NEMATODES AND THEY ARE NOT FOOLING ME?
Unfortunately, in order to carry out this check, we cannot trust what our eyes see.
It is even possible that by reducing the number of nematodes present in the soil, the plant did not achieve the necessary stimulus to continue growing, as the crop was very affected.
What you have to do is require an analysis carried out by a laboratory specialized in nematology , where a count of the number of nematodes is made for a sample, before and after carrying out the treatment.
With this you can know the exact number of individuals present in the sample, males, females, juvenile states (J1, J2, J3 and J4).
Normally, from the J2 juvenile stage is when the infection begins to occur. It must be taken into account that the female lays between 600 and 1,000 eggs in each laying, and they usually have a high survival rate.
Therefore, a good nematicide product would be based on making an effective attack on juvenile levels, such as J2, to make the population unable to regenerate.
However , the moment of application is also important, and many good nemtaticides have gone to the phytosanitary cemetery for not knowing how to use them correctly. C
As they say, the good farmer makes the product good.
THE RIGHT MOMENT OF APPLICATION DETERMINES THE EFFECTIVENESS OF THE NEMATICIDE PRODUCT
If we have an effective nematicidal solution for the young stages of the nematode, it will be interesting to spend it on the first irrigations at the beginning of the crop.
This is because this microscopic worm needs moisture to activate and reproduce.
When the earth is moistened, the change occurs, in the specific case of Heterodera , from egg to J1, from J1 to J2 and from J2 to J2s.