Nematodes cause losses of more than 50% in soybean and cotton crops in western Bahia

Nematode infestations in rainfed areas have drastically reduced soybean and cotton productivity in western Bahia (BA). The Nematodes in Rainfed Areas panel, led by professor Pedro Soares, during the 37th Brazilian Nematology Congress, held in Ribeirão Preto, addressed crop losses and highlighted the best forms of management.

According to Pedro Soares, in western Bahia, productivity losses associated with the presence of nematodes have exceeded 50% in soybean and cotton crops. These parasites attack plant roots and impair the absorption of water and nutrients. National agribusiness accounts for losses of more than R$70 billion annually due to the parasite.

"We have cotton areas in Bahia where productivity was greater than 300 arrobas per hectare, but after a nematode infestation the producer only harvested 100 arrobas per hectare", explained Pedro Soares.

In soybean cultivation, he says that there are rural producers who lose 50% of the crop. "Where the average harvest would be 70 bags of soybeans per hectare, the producer only harvested 50%", he states.

The species with the greatest economic importance in cotton are the root-knot nematode (Meloidogyne incognita), the reniform nematode (Rotylenchulus reniformis) and the root lesion nematode (Pratylenchus brachyurus).

Pedro Soares suggests integrated management to obtain better results. "The managed soil encourages the formation of deep and more voluminous roots, the choice of cultivar according to the species present, predominant and/or most harmful to the crop, combined with the use of chemical and biological products, aiming to protect the roots", observes the teacher.

The first step, before defining the practices to be used, is to make a good diagnosis, identifying which species are predominant and are most harmful to crops present in the area. "It will be necessary to collect soil and root samples, carry out a nematological analysis, carried out in a reliable laboratory, as well as, we must consider the history of crops in the area", he assesses.

"The first sign of nematodes in crops is a decrease in crop productivity. If practices to reverse this situation are not used, the traditional symptoms of nematode occurrence will appear, such as: occurrence of reboleiras, with dwarf plants, with nutrient deficiency, poorly developed roots and symptoms of being sick, due to the presence of nematodes. Losses in this case will be above 30%, in general", he analyzes.

According to him, despite visual identification, the most accurate and efficient way to detect the high presence of nematodes in crops is through laboratory testing with the collection of soil and possibly infested roots.

"In this way, it is possible to be sure of the predominant species that are most harmful to crops, for later definition of the most efficient practices that will provide greater productivity and profitability", he emphasizes.

Among the actions that can help control nematodes in crops, Pedro Soares highlights crop rotation with resistant, immune and low RF (reproduction factor) species or cover crops, soil correction and balanced fertilization, choice of the appropriate cultivar in function of the predominant species, use of biological and chemical control. "Brachiaria is an excellent coverage alternative and is well accepted in this region."

Three consultants also participated in the panel. The consultant and manager of Gran7 (BA), Maria Ângela Gorgem, highlighted management practices to minimize nematode infestations, including mechanical intervention to maintain contour lines; soil correction because low calcium levels have increased the nematode problem; the use of resistant varieties, biological products, phytochemical nematicidal technologies, which do not interfere with the soil macrobiota and the use of fertilizers, which have an action on nematodes, among other practices. "There's no point investing in fertilizers, in nutrition if there's a little bug eating the root", she adds.

Consultant Israel José da Silva, from Multicrop, in Bahia, advocates a set of practices that contain biological and chemical tools and, above all, a good cultivar. "These practices combined with integrated soil management have been used with good results.

Agronomist and consultant Henry Sato, from Datafarm, in Campinas, also participated in the event, who recommended cover plants for soil management with a focus on productive efficiency and environmental sustainability.

Those who were unable to participate in the 37th Brazilian Nematology Congress can have access to the lectures by registering for R$300 via event website. The lectures were all recorded and will be available for up to six months after the event, which took place from August 1 to 4, 2022.