We have already had the opportunity to point out in an article published a few weeks ago, how Nematodes are a far from negligible concern in agriculture. The horticultural sector in particular, often finds itself having to deal with the damage caused by these parasites, mainly by galligenic and cysticles ones, which live at the expense of the root systems, but also by species that feed off the epigeal systems.
Nematodes: let's learn how to recognize them
Nematodes owe their name (from Greek etymology: nema, thread; éidos, appearance) to their body, in most cases anguilliform – vermiform, equipped at the cephalic end (usually larger in size than the caudal one, which tends to be more pointed) with a stiletto shaped mouth apparatus, with which the Nematodes penetrate the tissues they extract nourishment from.
However, we need to immediately clarify the idea that all nematodes are parasites and therefore potentially harmful to plant crops.
From a trophic point of view, there are in fact various Nematodes:
- saprophytes, which feed on decomposing substances;
- predators, which feed on small animals (including harmful insects);
- phytomizes, which feed at the expense of live plant tissues and fungi.
Phytomize nematodes in turn can be:
- ectoparasites: only the stiletto is introduced into the host plant at the time of feeding;
- semi-endoparasites: the front half of the nematode’s body enters the host plant;
- endoparasites: the entire body of the nematode settles inside the host plant.
Phytomize nematodes can also feed at the expense of the epigeal organs or the root system. In the specific case of vegetable crops (also depending on whether the crop is root, leaf or stem based) in both cases the damage may be worthy of attention and require taking all possible actions to prevent infestations, as well as adequate phytosanitary interventions in the event of obvious attacks by these parasites.
Vegetable crops: which nematodes should you fear?
The epigeal portion of some vegetables can be damaged by nematodes belonging to the genera Aphelencoides and Ditylenchus, which cause, for example, fruit deformations in strawberries and leaf curling in onions.
Much more fearsome, however, are the endoparasitic galligenic nematodes, in particular those belonging to the genus Meloidogyne, which damage the root systems of numerous vegetable crops, and are particularly dangerous for solanaceous plants (potato, tomato, eggplant, pepper), cucurbits (pumpkin, zucchini, melon, watermelon, cucumber) and umbelliferae (carrot).
Finally, endoparasitic cystic nematodes belonging to the genus Globodera are quite fearsome for potatoes. Direct damage from galligenic nematodes and cysticles manifests through leaf yellowing, stunted development of the epigeal organs, wilting due to reduced and/or inefficient root activity, and the formation of galls and cysts. The roots often show normal development and, in the specific case of the carrot, can undergo bifurcation of the taproot.
Possible secondary damage common to all parasitic nematodes is represented by rot from fungi of the genera Fusarium and Rhizopus, festering in the lesions caused by nematodes, and by viruses transmitted by the nematodes themselves during trophic activity.
Managing the Soil to Prevent Nematodes
The choice and correct management of the soil play fundamental roles in the prevention of nematode infestations in vegetable crops, together with crop rotations and targeted techniques, such as sunburn and green manuring with nematocide essences. This is not only done in the case of terrestrial nematodes, but also with those that live at the expense of the epigeal systems, since these too, in the absence of host plants, can survive encysted in soil for a period of up to 3-4 years.
Nematodes normally live in the first 15 cm of soil (although in the event of an infestation it is possible to find them even at a depth of 1.5 meters), a fact that allows us to affirm that for all vegetable crops, the layer explored by the root systems may be affected by the presence of nematodes.
The settlement and spread of nematodes in the soil is promoted, in addition to higher temperatures (which is why spring-summer vegetables are normally the most affected as well as those grown in greenhouses) by water imbalances and the poor biological fertility of soil. An adequate supply of organic matter, acting positively on the physical properties of the soil, creates unfavourable conditions for nematodes and at the same time promotes biodiversity and proliferation of microorganisms with proven inhibitory action against nematodes. Among these are the antagonist fungi belonging to the genera Paecilomyces, Pochonia and Arthrobotys and the bacteria Bacillus firmus and Streptomyces avermitilis, with adulticidal action.
Parasitism explained with the mother-in-law example
In “Plant Disease: An Advanced Treatise”, published in 1978, James G. Horsfall and Ellis B. Cowling explain the possible relationships that are established between plants and others organisms, from trophic to parasitism and/or pathogenesis relationships: “Living in a commensal relationship with your mother-in-law is an uncertain situation. If she is a delightful lady who contributes financially to the cost of her room and board by never complaining about the children, you have mutual symbiosis. If she depends on your income and joins the family for meals, but does not complain, you have parasitism, but not pathogenesis. If she is a constant source of irritation for the family, you have pathogenesis, whether she pays the expenses or not: if she pays her share it is only a pathogen, if she does not pay, her behaviour is parasitic and pathogenetic.”
The Terrapiù line by Agribios offers a variety of products for professional horticulture that are all allowed in organic farming, able to counteract the development of nematodes.
FIRAV R is a liquid fertilizer made with Bacillus firmus and Streptomyces avermitilis, which exert adulticidal action against nematodes.
NEMAG R is a liquid organic fertilizer that, in addition to having an high-protein organic matrix, contains fungi of the genera Pochonia and Artrobotrys, with marked ovo-adulticidal action against nematodes.
NEMAKIL 330, with Nitrogen, Phosphorus and Calcium, and NEMAKIL 400, with Nitrogen, Iron and Calcium, are organic fertilizers that, by providing a highly humidified organic fraction, favour root development and plant growth, counteracting the damage caused by any Nematode attacks and at the same time discouraging their spread in the soil.
NEMAPLUS is an organic fertilizer in pellets with inoculation of mycorrhizal fungi. In addition to providing humidified organic matter, it contains the fungus Pochonia clamydosporia, with an inhibitory action against nematodes.