Expert chat with Professor Pedro Soares, Assistant Professor, University of the State of Sao Paulo (UNESP), Brazil

Prof. Pedro Soares

Professor Soares has worked with nematodes for more than 20 years. He remains fascinated by nematodes over all this time due to the huge loss of crop productivity they cause, the enormous challenge to control them and their fascinating bio ecology.

 

Can you give us a bit of background on soybean cyst nematodes in Brazil?

Tropical conditions, as we have in Brazil, are very favorable for all nematodes. With monoculture or rotation of crops that are hosts for nematodes, it only gets worse. The soybean cyst nematode (Heterodera glycines) is the most aggressive nematode for soybean in the world, but has a narrow host spectrum: soybean and species of fabacea. Because this nematode is very persistent in the soil, the use of resistant varieties of soybean apnd the rotation with other non-host crops is needed to reduce the soybean cyst population in the soil. The use of chemical and biological control can help, as well. In general, the use of resistant varieties can select for resistant races; so, the rotation of non-host crops and other forms of control is very important. In Brazil temperatures, the lifecycle of soybean cyst nematodes is 20 days – which essentially means five to six lifecycles per soybean growth cycle. The damage of this nematode can result in up to 50 % yield loss. One of the greatest challenges when a specialist wants to do something against nematodes on crops has been that growers are not convinced of the negative effects and losses that nematodes bring, and consequently, the need to control this pest. As a result, they increase their problem substantially, which makes the control more difficult. Over the years, the soil is not profitable for soybean production anymore. The damage they cannot see, they have difficulty in believing. This knowledge has to be made known to create consciousness of the losses that nematodes bring and the need to control them.

Professor Soares, when you speak about nematodes it becomes clear quite quickly that you are well-aware of what is happening in the field. How often do you get out into the field, as lecturer at the University of the State of Sao Paulo (UNESP)?

I need to understand the grower’s challenges and the problems, as well as the effect that nematodes are causing in their crops. For that, I go out to the field very often to understand them. In my view, nematology cannot be done only in the university laboratory because its study includes the impact that nematodes cause in crops. The need to know and see the effects that cultural practices and environmental factors associated with nematodes cause in the crops is extremely important. We also learn a lot from the growers and their experiences.

What do you think is key to managing soybean cyst nematodes?

What is needed is a combination of as many different measures as possible. A good strategy is the use of a resistant soybean variety for two to three years, followed (depending on the level of infestation) by one rotation of corn with bracchiaria. After the harvest of the corn crop, the bracchiaria can be used as cattle feed. After that, a susceptible soybean variety can be planted. Additionally, a seed treatment with a chemical nematicide /or biological control agent should be used. But all this depends on the level of nematodes in the roots and in the soil. To select the best sequence of steps, an analysis of soil and roots should always be done, helping us to choose the best control practices for each situation.

 What is the biggest challenge?

The biggest challenge is to convince the grower to use the most efficient practice to control nematodes – mainly because these practices may be not as lucrative as growing a soybean crop. Because growers are not believers or convinced about the problems that nematodes can bring, they rather tend to use practices that are less efficient to control the problem, but which are more profitable. This can become a big risk for soybean productivity over the years. It can put the area at big risk to become unprofitable for the growth of soybean in a few years.

What is the impact of this challenge?

A high infestation level with soybean cyst nematodes requires that the grower must use a resistant variety even though this practice just gives back 50% of the production which a susceptible variety could bring. It is very common to see loses up to 50%. Areas with high soybean cyst nematode infestation can reach up to 100% loses, making the area unprofitable for soybean production. In Brazil, we see significant losses caused by nematodes in soybean and other cultures, representing billions of dollars annually. The lack of a good practice to control root-knot nematodes, and other factors, in coffee, for example, made the coffee production migrate from the state of Rio de Janeiro to Sao Paulo (and other states) due to the loss of profitability. If the right practices are not applied in soybean growing areas to control the soybean cyst nematodes, the migration of the soybean to other areas will also be necessary. 

What other nematodes are relevant for soybeans in Brazil?

Other key nematode species we see are these:

  • Pratylenchus brachyurus (lesion nematode)
  • Meloidogyne javanica (root-knot nematode)
  • Meloidogyne incognita (root-knot nematode)
  • Rotylenchulus reniformis (reniform nematode)
  • Aphelenchoides besseyi (leaf nematode) causing crazy soybean II disease
  • Tubixaba tuxaua
  • Scutellonema brachyurus (spiral nematode)