“The use of chemical nematicides is not a ‘shield’. For nematode control, nematicides are not enough to exterminate the nematodes in an area…”
Luanna Karoline Rinaldi is a phytopathologist and nematologist at the Laboratory of Agronomic Analysis – Labortest, in Katueté, Paraguay.
Rinaldi is an agronomist with a degree from Centro Universitário Assis Gurgacz, has a master’s degree in plant production from the State University of Western Paraná and a Ph.D in plant protection from the State University of Maringá.
AgriBrasilis – What are the different nematodes of agricultural interest and what damage can they cause? Which cultures are most affected?
Luanna Rinaldi – Among the phytonematodes that cause damage to agriculture, we can mention four main ones:
Root-knot nematodes (Meloidogyne spp.) – Cause root thickening in the form of nodules. The root system becomes inefficient in absorbing water and nutrients, seriously affecting plant growth. They are parasites of various plants, such as tomatoes, peppers, soybeans, cotton, coffee, corn, potatoes, carrots, etc.
Cyst nematodes (Heterodera glycines) – Leave plants less vigorous, yellowish and stunted. It causes the formation of stunted roots, with a decrease in the number of nitrogen fixation nodules, making them more susceptible to infection by other soil pathogens. Among the hosts, soybean, beans, peas and lupine stand out.
Lesions nematodes (Pratylenchus spp.) – Cause necrotic lesions in the root system and attack mainly the rootlets, destroying the entire apparatus for absorbing water and nutrients, reducing productivity. They mainly affect grasses such as rice, wheat, corn, forage, sugar cane. They also affect cotton, soybean, coffee, citrus, potato, ornamental plants, vegetable crops, etc.
Reniform nematode (Rotylenchulus reniformis) – There is a decrease in the volume of plant roots, resulting in lower absorption of water and nutrients, in addition to reducing the size of the plant. It usually occurs in spots along the farm. Main crops affected are: cotton, soybean, tomato, watermelon, melon, passion fruit, beans, among others.
AgriBrasilis – What alternative nematode control methods exist? Are they as effective as chemical control?
Luanna Rinaldi – Some alternative nematode control methods can be used, such as crop rotation, use of antagonistic plants, traps, use of non-host plants or resistant cultivars, solarization, fallowing and the use of biological products.
These methods are efficient, but must be used together. Ideally, the farmer should invest in a set of practices and tools that will help in this process.
Chemical management for nematodes is a great tool to ensure establishment of an initial plant stand, less multiplication of nematodes at the beginning of the crop cycle, ensuring better development and more tolerance of the plant in relation to nematode parasitism after the residual period of the nematicides.
The use of chemical nematicides is not a “shield”. For nematode control, nematicides are not enough to exterminate the nematodes in an area, as this is practically impossible. The use of the tool guarantees a better coexistence with the nematodes.
As for alternative methods, the use of agrochemicals also has better results when integrated with other management practices.
AgriBrasilis – Is the texture of the soil also a factor that impacts these populations? Because?
Luanna Rinaldi – Yes. The more sandy the soil, the more easily the nematode will move around, either on its own or due to external factors. This will facilitate its arrival to the host, increasing its population, as well as increasing its spread and making it difficult to control.
Another point is that clayey soils have a higher fertility than sandy soils. This influences the level of damage that a nematode population can do.
AgriBrasilis – How is the identification and quantification of phytonematodes done?
Luanna Rinaldi – It is carried out in a specialized laboratory in which the organisms are extracted from soil along with roots samples and with the aid of a microscope and stereoscope, the identification and quantification of the phytonematodes is done.
Identification is commonly based on the morphological characteristics of the population. However, the physiological, cytogenetic, serological and molecular characteristics make it possible to deepen and establish morphologically similar differences between taxa.
AgriBrasilis – What is the relationship between phytonematodes and other organisms present in the soil?
Luanna Rinaldi – Phytonematodes can also cause indirect damage and limit crop development. The result of the action of phytonematodes on the roots is the formation of epidermal lesions, either by suction of the sap or by the entry of the nematode into the root tissue.
Lesions in the root tissue provide contact with soil pathogens, that is, they represent a gateway for these fungal agents, which will cause damage to the plant.