How to combat nematodes that affect soybean crops

The animal group called the phylum Nematoda includes roughly cylindrical, round worms known as nematodes. The most familiar to the general public, mainly due to their large size, are roundworms, common parasites of the digestive tract of humans and other vertebrate animals.

Nematodes are basically aquatic animals, although they can be found in almost any type of environment, as long as there is at least a film of water to keep them moist. There are about 80 thousand species of nematodes already described, but it is estimated that the total number of living species is approximately one million. The vast majority of them are microscopic organisms, not visible to the naked eye, measuring from 0,2 mm to 2 mm in length.

A few forms, generally parasitic on animals, are much larger, measured in centimeters or, rarely, meters. The largest known nematode is Placentonema gigantissima, about 8m long, found in the placenta of a cetacean mammal, the spermaceti whale.

In 2007, AgroLab Sociedade de Pesquisa Agrícola was established in Primavera do Leste (Mato Grosso), with the development of nematology laboratory activities, to operate in the states of Mato Grosso and Mato Grosso do Sul.

In the 2007/08 agricultural year, there was a demand for 280 samples, covering the months of September to May.

After seven years and based on the 2013/14 agricultural year, AgroLab carried out analysis of more than ten thousand samples for nematodes.

Of the samples analyzed, around 60% came from producers, the other 40% are from outsourced georeferencing companies that provide services in this segment, developing nematode mapping from physical/chemical soil samples, identifying any decrease in production. .

In Mato Grosso, the most cultivated crops are soybeans, cotton and corn and, to a lesser extent, in more specific regions, the cultivation of beans, rice, sunflower and sugar cane.

All of these crops are susceptible to the presence of nematodes.

The main nematodes found are: Meloidogyne incognita, Meloidogyne javanica, Heterodera glycines, Pratylenchus brachyurus, Rotylenchulus reniformis e Helicotylenchulus spp.

Based on the analyzes carried out up to May 30, 2014, a sample frequency survey was prepared, as shown in the table below:

Based on the region where AgroLab operates, it is possible to state that there are areas where the cultivation of any crop becomes unfeasible due to nematode attacks.

Most of the time, these microscopic organisms are distributed in the soil in the form of lumps and mixtures, that is, two or more species of nematode in the same area.

Nematodes are considered worms that need free water in the soil to move, and the rainy months are favorable for them.

With the absence or little humidity, they remain in the soil for a long time in the form of eggs or cysts in the case of Heterodera glycines.

During the rainy season, the damage is less visible, however, the nematode multiplication is greater. Dry periods favor the detection of symptoms, although multiplication is slower.

The problem worsens in areas with low levels of organic matter, sandy soils, problems with fertility/correction, depth, etc. Fertile, well-amended soils are less damaged by the action of nematodes and the damage is less visible. Common problem in almost the entire Midwest, due to sandy soils.

It is possible to say that nematodes are found throughout Brazil, wherever food can be found, they settle or are “taken” by human action, transport or contamination and dissemination through water, rain, irrigation, wind, vehicles, various agricultural machines, etc. .

In fact, any soil particle is capable of carrying nematodes. Present in an area, it becomes difficult and even impossible to eliminate the incidence completely. Control practices are based on strategies for coexisting with nematodes.

What to do once this “invisible enemy” has been identified?

Once the problem, the species of nematode and the populations have been identified, the important thing is to know what should be done to control it, as any failure will only contribute to population growth, making agricultural cultivation in the affected area unfeasible.

For control, it is necessary to identify the species present in the area, as there are different alternatives for each species. The most common species and probably widespread throughout Brazil is the root lesion nematode (Pratylenchus brachyurus). This nematode feeds on almost all crops, which makes it strong and difficult to control.

The main control measures are: use of resistant cultivars, adequate soil management, planting of crops that reduce population numbers, biological products and chemical products. The important thing is to carry out as many simultaneous controls as possible, as an isolated practice may be unfeasible.

Use of vegetation cover

Vegetation coverage leads to greater water storage and improvement of the physical, chemical and biological attributes of the soil. The crop, in turn, would benefit from increased biological activity in the soil, thanks to the organic matter produced by the vegetation cover, which also ensures more adequate thermal conditions.

Furthermore, direct sunlight, due to ultraviolet radiation, has a negative effect on microorganisms that control nematodes. Therefore, soil cover will provide favorable conditions for the development of soil microflora.

It is possible to mention several successful practices, such as planting Crotalarias, consortia, planting resistant millets such as ADR 300 or ADR 8010, among other coverages.

Biological control

Biological management aims to create unfavorable conditions for the development of these pathogens, increasing biodiversity and improving soil structure. Therefore, although nematodes are present, their population is under control and the damage caused to the plant is minimal.

More than 200 different organisms are considered natural enemies of phytonematodes. These nematophagous microorganisms are normally found in the soil, parasitizing eggs or cysts, preying on juveniles and adults or even producing toxic substances that are harmful to the pest.

The controlled insertion of these microorganisms through commercial formulations is an excellent way to control nematodes. It is possible to call this method biological control, since it is another living organism that will control the disease.

Among the microorganisms with proven nematicidal effect are Paecilomyces lilacinus, Trichoderma harzianu, Arthrobotrys oligospora, Arthrobotrys musiformis, as well as some rhizobacteria.

Use of resistant cultivars

It is one of the most attractive methods, as in addition to not involving additional costs, it does not cause environmental impacts because, even in already infested areas, it does not require the use of chemical products.

It is worth remembering that there are still no species on the market resistant to the main types of nematodes, especially Pratylenchus.

Currently, research companies are very engaged in testing materials and “discovering” a source of resistance to this nematode.

crop rotation

The lack of crop rotation is one of the main reasons why nematodes have advanced so much in crops. The practice is one of the best and most used methods of controlling phytonematodes, since it is low-cost and does not pose a risk of toxicity to humans and the environment, in addition to improving the physical, chemical and biological conditions of the soil, making it more productive.

The choice of crop for rotation will depend on the results of the nematological analysis, as a plant may not be host to a certain nematode, but to another, increasing biodiversity.

Healthy soil is teeming with all kinds of life, from microscopic bacteria and fungi to more visible creatures like earthworms, beetles, slugs, and other insects. Many of these creatures are responsible for recycling organic matter and decomposing it, so that the nutrients it contains are once again available to plants.

The activities of microorganisms also help build soil structure.

chemical control

Not long ago, chemicals were considered the villains of history, always very toxic and with some undesirable side effects. Currently, this view is changing, chemicals are becoming less toxic, especially to humans, and more efficient.

There are some extremely efficient chemical products for reducing nematode populations, some in seed treatments and others applied in furrows or in ground spraying. What matters is that all control segments are evolving, most national and multinational companies have strong research in this area of ​​nematology. There will probably be many control options soon!

Finally, it is important that the producer does not close his eyes to this “invisible enemy”, takes measures regarding control, so as not to make his agricultural production unviable.

By Tatiane Zambiazi, AgroLab

This article was published in issue 183 of Cultivar Grandes Culturas magazine. Click here to read the edition.