Controlling nematodes requires every tool available

According to Guilherme Lafourcade Asmus, researcher at Embrapa Agropecuária Oeste, the first references of occurrences of phytonematodes in the Cerrado of Mato Grosso date back to 1970. The first surveys showed the presence of ten species, including Meloidogyne, Aphelenchoides and Pratylenchus brachyurus, with 16,7 .13,3%, 3,3% and XNUMX%, respectively. At the time, they were sporadic, but they were already causing huge losses to farmers.

The time frame occurred in the 1991/92 harvest, when the soybean cyst nematode (Heterodera glycines) appeared for the first time, simultaneously in the Triângulo Mineiro, Mato Grosso do Sul and MT. “It was a milestone because this nematode, unlike what had happened until then, caused very severe damage that had an impact not only visually but also on the producer's pocket,” explained Asmus.

This information was part of the talk show “Damage caused by phytonematodes in the Cerrado”, presented this Thursday afternoon (28) during the XXII Soya Technical Meeting of the Mato Grosso Agricultural Research Support Foundation (MT Foundation), in Cuiabá- Mt. Along with the researcher, the institution's nematologist and researcher, Rosangela Silva, Júlio Franchini, from Embrapa Soja, and Henrique Trevisanuto, from PA Consultoria, contributed to the topic.

Impactful changes

From the cyst nematode, producers and researchers were able to understand that this was a problem with more specificity for the soybean crop. And every year they stopped sowing this crop, populations reduced by up to 70%. Summer corn then became an excellent option in crop rotation. “There was this change in attitude, with other options such as cotton and sugar cane. But there was an expectation of returning to “normality”, and this improved when the first soybean cultivar with resistance to cyst races 1 and 3 appeared”, explained the Embrapa researcher.

Along with this, direct planting increased, the rotation with millet and perennial forage grasses also increased, in addition to the intensification of land use with the succession of crops - safrinha corn with brachiaria (or not) and soybean-cotton. During this period, the genetic improvement of soybeans was focused on breeds 1 and 3, but in Brazil and, especially in the Cerrado, a true “fruit salad” of breeds became a reality. “And today, we have the presence of many species, large areas with nematodes and, recently, a worrying increase in the species Rotylenchulus reniformes. Those who grow cotton know that it is the most problematic. It does not cause drastic symptoms in soybean crops, the movements are less pronounced and this ends up confusing producers with other causes. And certainly the changes in posture were the vectors for the occurrence of nematodes today”, reported Guilherme.

Presence in Mato Grosso

Consultant Henrique Trevisanuto presented data from a survey with 1059 nematological analyzes carried out in plots in Mato Grosso, in the 2021/22 harvest. The survey concluded that 59% of the areas had a medium infestation of Pratylenchus, only 1% had Meloidogyne and 3% had cysts, with more than 50% without this nematode.

Regarding cyst breeds, 334 samples were analyzed, with 61% having a frequency of breed 4, 16% of breed 14 and 14% of breed 2, totaling 91% with these three breeds in the harvest. “Races 1 and 3 appeared again, they had not appeared for many years. If we compare the evolution from the 17/18 harvest to this one (same type of survey), we see that the frequency of breed 2 did not change (from 16% to 14%), but breed 4 increased from 28% to 61% and the 14th fell from 44% to 16%”, contextualized the consultant.

He defined that what happened was not the solution to the problem but rather the selection of breed 4, which has fewer options for resistant varieties. The warning, therefore, is that simply using cultivars with resistance does not solve the problem, but rather prevent populations from rising through the use of other alternatives.

Producer's perception

Nematologist Rosangela Silva, who has been carrying out studies on nematodes in Mato Grosso since 2001, highlighted that producers' perception regarding nematodes has changed, but not enough. “Before, the producer came to talk to us, he said he had a nematode problem, but he didn’t know which one. Today he knows the species, the races, the perception has changed, but is it for all nematodes?”, she asked. The researcher added that for Rotylenchulus reniformes this perception still needs to be improved a lot, as there is a notion of damage to cotton, but not to soybeans, as the transfer from one crop to another continues to occur, causing loss of yield in both due to the parasite.

Since 2015, in evaluating soybean cultivars planted before cotton, the MT Foundation has been studying how much of the legacy of this species they leave for the cotton crop. “We see that the majority have a high reproduction factor (FR), generating this transfer, and those that have a low FR, very interesting, generally do not have an appropriate cycle to precede this crop that comes in the second harvest. So we continue with the problem. I say this to show that we need help from breeding companies in this regard”, explained Rosangela.

How to proceed

For Júlio Franchini, it is necessary to improve the environment to make it more favorable for the plant and unfavorable for the nematode, using rotation with non-host crops, which also improves the soil structure. “The nematode is there, we have to live with it. The cover provides soil protection, thermal regulation and reduces water loss through evaporation. You create a better environment for the plant, the mulch will bring more straw, more roots,” he described.

The researcher continued asking whether the nematode was the cause or consequence. “I think it causes damage when there is high infestation, in an environment that is favorable for it and unfavorable for the plant. But I think that inadequate management has a lot of causes. In the case of Pratylenchus we have high populations and no damage, at other times the opposite. So we cannot attribute it to the fact that it multiplied or not multiplied, it is not the only observation to be made. The entire management integration is the difference”, he highlighted.

Rosangela recalled that the work of Fundação MT at CAD Sul, in Itiquira-MT, also has good results in reducing nematode populations through the practice of crop rotation. The test has existed since 2008, using limestone to show the variation in soybean cyst nematode. “With the planting of millet in the area, the population took longer to start rising, showing that soil biology has a big impact. Furthermore, in plots with off-season crop rotation (first soybeans, then rotating with brachiaria, corn and sunn hemp) it took even longer for populations to increase. This shows us that the most biologically active soil offers a buffer effect for nematodes, the balanced chemical and biological part is also of great importance”, stated the specialist.

This experiment also showed that with these practices productivity is very interesting, with a difference of 31 bags to 70 bags per hectare in the plots in general. “The chemical part of the soil is extremely important, but we also cannot fail to worry about cultural management, which is extremely important”, added the nematologist.

Learnings

For Franchini, agriculture is not philanthropy. “Today we have tools to overcome difficulties. The ideal is to start predicting before the nematode occurs. When we are in a situation that is no longer sustainable we have to attack. In an organized way, plot by plot, trying to minimize over time”, he concluded.

For Trevisanuto, good planning, looking at the long term and not being short-sighted is ideal. “For example, thinking that biologicals will pay off in the future. It is better to lose 10 bags of corn with the intercropping, but gain in the subsequent five years by doing the practice, and improving soil biology. Today we have clients who harvest soybean plots of 87 bags, but they have spent seven years with a consortium, five years with organic farming in the area, they make limestone every year. And speaking of the issue of fertilizer, imagine who hasn't taken care of nematodes in recent years and is going to cut back on fertilizer? So the reflection remains”, he highlighted.

Researcher Guilherme highlighted that the nematode is an indicator of the quality of the production system, and when it becomes a problem it is because something is wrong. “It is necessary to carry out nematode analysis and soil analysis, they do little. We produced well, it rained well, we harvested up to 80 bags, but we are not taking into account the need to replace nutrients. The issue of fertility is homework. Reduce variability within the area, make it more homogeneous, with fewer regions with problems for plants. Use more consolidated tools, maintain a good environment for the plant”, he concluded.