“…annual losses of over US 2.75 billion due to soybean nematodes…”
José Mauro da Cunha e Castro is a nematologist at Embrapa’s Soybean Unit, graduated in agronomy, with a M.Sc. and Ph.D. in phytopathology from the Federal University of Viçosa.
Maurício Meyer is a phytopathologist at Embrapa Soybean, graduated in agronomy from UEPG, with a M.Sc. from the University of Brasília and Ph.D. from Unesp.
AgriBrasilis – How much is lost in Brazil due to nematodes in soybeans?
José Mauro – Estimating losses caused by nematodes in a wide range of crops is not an easy task. However, in Brazil, recent data indicate annual losses of over US 2.75 billion due to soybean nematodes. When the effects of other disease-causing agents are added, approximately US$ 11.02 billion are lost annually in profitability in crop production, which means that one in every 10 harvests does not return any profits to the farmers.
AgriBrasilis – How has the green stem nematode (Aphelenchoides besseyi) infestation evolved and what damage has this pest caused?
Maurício Meyer – The incidence of the green stem soybean nematodes has gradually increased in tropical soybean regions, characterized by hot and rainy weather, in the States of Maranhão, Pará, Tocantins, Mato Grosso, Rondônia, Amapá and Acre. The soybean production area with the highest risk of green stem nematode incidence corresponds to approximately 6.3 million hectares.
Productivity reductions of up to 60% have already been observed in soybeans, mainly in areas where the invasive plants are still green after fallow. In addition to soybeans, the green stem nematode also attacks cotton, causing productivity reductions of up to 35% in this crop, in second-season crops after soybeans.
Other crops of economic importance that may be affected by the nematode, despite there being no records of significant losses in Brazilian crops, are common beans, chickpeas, sesame, white oats, chrysanthemums, cowpeas, tobacco, yams, rye and asplenium.
AgriBrasilis – In addition to A. besseyi, what are the main nematodes in soybean areas?
José Mauro – Meloidogyne javanica e M. incognita, known as root-knot nematodes, Heterodera glycines or cyst nematode, Pratylenchus brachyurus or root-lesion nematode and Rotylenchulus reniformis or reniform nematode are the most widespread soybean nematodes.
Helicotylenchus dihystera (spiral nematode), Scutellonema brachyurus and Tubixaba tuxaua can also be found in some crops, with the first two causing root darkening similar to that observed in cases of P. brachyurus infection.
AgriBrasilis – What measures are recommended for controlling nematodes?
José Mauro – Several measures can be used to control soybean nematodes.
The measures most commonly recommended and adopted by farmers are:
- Crop rotation/succession
- Sowing of resistant cultivars
- Sowing of antagonistic crops
- Biological control using fungi and bacteria-based products
- Chemical control
No-till farming is based on crop rotation, with the production of straw that covers the soil being part of the management. In addition to helping to fix carbon in the soil and minimize the greenhouse effect, no-till has the great advantage of reducing movement through plowing and harrowing, helping to reduce the spread of nematodes in soybean farms.
AgriBrasilis – What are “antagonistic” plants and why are they important for nematode control?
José Mauro – Antagonistic plants are attractive to nematodes, but after penetration, they do not allow the nematodes to form feeding sites or establish themselves in their roots. Thus, the death of nematodes due to lack of food is an important measure for population reduction.
Several species of Mucuna and Crotalaria are antagonists, especially in relation to the most common root-knot nematodes in soybeans. Thus, C. spectabilis and C. breviflora are efficient in controlling M. incognita and M. javanica, but good results in controlling these nematodes are not always achieved with the sowing of C. juncea and C. ochroleuca. These species of Crotalaria and the Mucuna are also not recommended for the management of P. brachyurus in farms intended for agricultural production.
As another strategy, antagonism to nematodes can be conferred by the release of toxic substances by the roots of some plants, as is observed with marigold species (Tagetes spp.) that release alpha-terthienyl into the soil, a substance that is toxic to plant-parasitic nematodes.
AgriBrasilis – Why are chemical products not as effective as bionematicides?
José Mauro – Chemical products or nematicides and biological products or bionematicides occupy distinct and equally important spaces in nematode management/control. Currently, the complementarity of products from both classes has been observed and the application of chemical and biological products in the same season has been adopted in different crops. Chemical products, as a rule, are more expensive, more toxic to the environment and animals, including to humans, and present a greater risk of selecting resistant organisms within the nematode population in the soil, but, even so, they should not be left aside in the process of defining the strategies to be implemented on a farm.
Biopesticides, however, can be less expensive, are less harmful to the environment and animals, have a good residual effect through the establishment in the soil (which does not eliminate the need for reapplications) and, therefore, have been gaining ground, including in large-scale crop production. One aspect that deserves to be highlighted regarding the use of biological products for controlling pests and disease-causing agents in crops is the special registration process regarding the target and not the specific crop, with the Ministry of Agriculture and Livestock.
READ MORE: