When is the best time to collect samples for soybean nematode diagnosis?

Evaluating the last soybean harvest, especially in Mato Grosso and the Center-West, the increase in the incidence of nematodes in crops was evident. The warning comes from researcher and nematologist from the Mato Grosso Agricultural Research Support Foundation (MT Foundation), Tânia Santos, who emphasizes that it is necessary to keep an eye on management for the 2022/23 cycle.

To guide and resolve doubts, mainly about the right time to identify these pathogens, the institution is holding today, Tuesday, 25th, from 19pm MT, the free live stream “É Hora de Cuidar”, with the participation of Tânia and also researcher and doctor in phytopathology, Rosangela Silva.

One of the themes of the event is monitoring and the right time of collection for the evaluation of nematodes. This issue is highlighted by specialist Tânia as fundamental to successful management. “The ideal is to always monitor the symptoms in the aerial part of the crop, generally, we observe spots in reboleiras, where the plants are small and yellowish, and where the affected leaves, sometimes, present chlorotic spots or necrosis between the veins, characterizing the leaf 'carijó'”, he reports.

It can still happen that there is often no reduction in the size of the plants, but during flowering, according to her, pods can abort and premature ripen. “Commonly, these symptoms are not so evident, which is why it is important to carry out nematological analysis to identify the type of nematode and the population present”, he reinforces.

Collecting soil and roots whenever you identify or observe any symptoms, or when there is a drop in productivity in the previous harvest, are other recommendations from Tânia. She also highlights that it is necessary to send it to a trusted laboratory for analysis. “The right time to collect these samples is at the beginning of the soybean crop’s flowering until maturity. This is the ideal period, because the nematode completes two to three cycles in the roots of the plant”, says the professional.

Villains of various vintages

The problem with nematodes in Mato Grosso has increased in recent years, and the biggest concern is: Meloidogyne javanica, Meloidogyne incognita and Heterodera glycines, and not least the lesion nematode, (Pratylenchus brachyurus), frequently found in soil samples and roots. However, we still have Rotylenchulus reniformis, which may not cause losses in soybeans, however, in the subsequent crop, as is the case with cotton, and even more significant losses.

The increase in the population of these pathogens is not only occurring in the State, but also in the Central-West region of the country, which according to the MT Foundation researcher is due to monoculture (soybean/corn or soybean/cotton), and the use of soybean cultivars susceptible throughout the harvest.

How to perform sampling for nematode diagnosis

For the results to be in line with the reality of the farm, it is necessary to collect samples for diagnosis in the most correct way possible and at the right time. To collect soil and roots, it is recommended that these be done at the beginning of the crop's flowering, approximately 40 or 60 days after emergence. “We also recommend collecting these samples, whenever possible, on the edge of the reboleira, that is, from the rhizosphere. In the case of roots, special attention should be paid to radicelles, which should preferably be collected in the cycle before a new planting”, explains the researcher.

When collecting, use correct tools, such as hoes, mattocks and shovels. Always identify the packaging in which this material is placed, which is made of plastic so as not to lose the initial characteristics of the sample. “During sampling, you must walk in a ‘zigzag’ pattern, opening the soil in a V shape. Collect plants that show moderate symptoms, avoiding those with many symptoms or that are very depleted. In reboleiras, sample on the outskirts of it”, highlights the specialist.

Another important guideline is to collect at a depth of 0 to 25 or 30 cm. “With emphasis on obtaining 10 sub-samples in order to form a composite sample and then homogenizing it well and sending at least 1kg of soil and 20 grams of roots to the laboratory, properly packaged and identified according to the area sampled”, adds Tânia .

It is necessary to change

The damage caused by nematodes in soybeans is very significant, especially in the Brazilian Cerrado as a whole, where there are favorable conditions for their development and multiplication. For the researcher, the producer still needs to learn how to live with these pathogens, as once they are present in the area it is impossible to eradicate them. “That is why it is so important to make the correct diagnosis of the species that is in the crop, combined with the use of management tools that have been proven to be efficient, based on research results, so that the situation can be improved”, she says.

Various management tools are available on the market, with different degrees of efficiency, depending on the work adopted by the farm. “We can point out resistant cultivars, crop rotation, use of chemical and/or biological nematicides and even cover crops to introduce organic matter into the system. It is up to the producer to analyze the cost/benefit ratio of each tool and choose the one that best suits their crop”, concludes the researcher.

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This and other information can be followed tonight (October 25th) during the MT Foundation's free online meeting, starting at 19pm MT. On that occasion, a team of researchers will be gathered to provide the best guidance on post-planting care. Registration can be done via website.