Management of nematodes in sugarcane

Differently than occurs in other crops, nematodes do not lead sugarcane fields to death. But the plants generally become smaller, with thinner stems, the clumps develop less and have fewer culms, the field as a whole becomes very irregular and not very productive. The use of chemical and biological nematicides is one of the strategies to minimize the damage caused by these parasites.

You nematodes cause reduced productivity in many important crops agricultural, such as soybeans, cotton, corn, coffee, oranges, and it is no different in relation to sugar cane. In sugarcane fields, many species of nematodes, but four are responsible for the greatest damage to Brazilian producers:  Pratylenchus zeae and P. brachurus, Meloidogyne javanica e M. incognita.

In agreement with DMLab – Agricultural analysis laboratory in Ribeirão Preto, São Paulo, who analyzes samples sent by producers from all over Brazil, P. zeae is, without a doubt, the most often found in populations high enough to cause harm economic in sugarcane fields, present in 97% of the samples analyzed. The species M. javanica e P. brachyurus are found in approximately 35% of samples, while M. unexplained is rarer in sugarcane fields, present in approximately 20% of the samples.

P. zeae is the most relevant species in sugarcane as it is the most frequently found in populations high enough to cause economic damage, as mentioned previously, but it is not the most pathogenic; In general, species of Meloidogyne are more pathogenic to sugarcane cultivars that the species of Pratylenchus. Thus, on average, pathogenicity decreases in the following order: M. unexplained,  M. javanica, P. zeae e P. brachyurus. Considering the frequency in which they appear in populations high enough to cause harm, the importance decreases in the following order: P. zeae, M. javanica, M. incognita, P. brachyurus.

The nematode attack sugarcane is restricted to the roots, from where they extract nutrients for growth and development. That attack on the root system occurs from the emission of the first roots, originating both from the sett and from the tillers sprouted from the buds. As nematodes inject toxins in the root system, deformations occur (such as galls caused by  Meloidogyne) and  extensive necrotic areas, when the nematodes present are Pratylenchus. As a result of nematode attack, the roots become poor in root cells and unable to absorb water and nutrients necessary for good development of plants, which become smaller, stunted, chlorotic, withered in the hottest hours of the day and less productive.

If in crops such as soybeans, tomatoes and coffee, among others, it is easily observed galls caused by Meloidogyne, in sugarcane fields this does not always occur, due to Due to the thickness of the cane roots, the galls often go unnoticed. Already root necrosis caused by Pratylenchus can also be confused in sugarcane by necrosis caused by certain pests, such as root leafhopper. Thus, the detection of nematode populations in Sugarcane plantations depend on analyzing root and soil samples in the laboratory. Such analyzes are even more necessary because nematodes do not cause the death of sugarcane plants, which is common in annual crops (soybeans, cotton, etc.) and even in some perennials. In sugarcane, plants generally they become smaller, with thinner culms; the clumps develop less and have fewer culms; the field as a whole becomes very irregular and little productive; but no dead clumps were observed due to nematode attack.

The damage caused by these parasites vary depending on the species present, the population of each of them, the type of soil, the variety of sugarcane and many other factors, but are on average between 20% and 40% productivity reduction in the first cut, which can reach more than 50%, in cases of very high population levels and very susceptible varieties. In ratoons, productivity is also seriously reduced, compromising the longevity of the crop, which needs to be renewed more often in infested areas.

 The magnitude of damage caused by nematodes in sugarcane and ratoon cane can be easily observed in the field, at least use of nematicide in infested areas compared to untreated areas: plants larger ones have smaller populations of nematodes in their roots due to use of nematicides, in planting or in brass knuckles.

An example of the damage caused by nematodes to the sugarcane plant is presented in Figure 1, which shows represented the reduction in productivity caused by nematodes in sugarcane fields, conducted in several infested areas, in which planting was carried out in different times of the year. To estimate such damage, the productivity of the sugarcane field, whether planted or not with nematicide in the furrow. In the example cited, nematodes caused a reduction in productivity ranging from 11% to 25%.

The damage caused by nematodes in ratoons are also relevant and can be noticed when carrying out nematicidal treatment or not in an infested area and compare productivity both of the treated area and the untreated area (control). An example of this is in Figure 2, in which the ratoon sugarcane was treated with both chemical nematicide (carbosulfan) as with biological nematicide (Bacillus subtilis + B. licheniformis).  

Both in sugarcane as in ratoon crops, the use of chemical or biological nematicides in areas infested results in a significant increase in sugarcane productivity, which which confirms the importance of nematodes in sugarcane.

Article published in issue 227 of Cultivar Grandes Culturas, April 2018.