How to control soil pests in sugarcane

Soil pests such as grubs, Migdolus, weevils, termites, root hoppers and hairy borers can cause serious damage to sugarcane. As a general rule, their control should preferably occur during crop preparation or planting.

Sugarcane crops are subject to frequent attacks by pests, which, depending on the stage of the plant and the intensity of the attack, can cause considerable damage if not controlled. Among the most important insect pests of the crop, the borer, Diatraea saccharalis, stands out, which can cause severe damage to the plants and, consequently, reduce their productivity. Likewise, pests associated with the soil also represent one of the main problems in the cultivation of this grass, mainly due to the intensity of losses they can cause to the crop.

Corós, which are also called bolo bugs or chicken bread, are beetles from the Melolonthidae family, little studied in sugarcane cultivation. These insects attack newly planted sugarcane setts and the basal internodes or rhizomes already formed, which can cause damage to the crop. The larvae are curved and white, with a brown head and clearly visible thoracic legs, reaching 50 mm in length and feeding on the sett, rhizome, sugarcane roots and organic matter. Near the end of the larval stage, these beetles build a chamber in the soil and transform into pupae. Adults generally emerge in the hottest months of the year, after the first rain, corresponding to the time when new canes sprout, and are normally attracted at night by bright spots.

Larvae of the Melolonthidae family are normally considered secondary pests of sugarcane crops in the country, with the main species being Eutheola humilis and others from the genera Liogenys, Cyclocephala, Lygirus and Stenocrates.

Migdolus sp

The Migdolus beetle is one of the most damaging species to sugarcane. The damage is caused by larvae that feed on and destroy the root system of plants at any age, which can lead to a significant reduction in the absorption of water and nutrients by the plants, causing them to dry out and die. In areas with high infestation of this pest, it may be necessary to replant.

The species M. fryanus is subterranean and lives in deep, well-drained soils, especially in cerrado regions. Males are active and fly, while females do not fly because their wings are atrophied. The larvae are milky white in color and measure approximately 40 mm when fully developed (Figure 3). Adults are light rusty (female) or black (male) in color, and have a long biological cycle, probably lasting more than two years.

Migdolus larvae are normally collected in soil trenches in sugarcane fields in various regions of Brazil. According to Machado et al (2006), M. fryanus swarms are observed between October and March in São Paulo.

Sugarcane weevils

Sphenophorus levis and Metamasius hemipterus are beetles known as weevils that belong to the Curculionidae family. These species are considered important pests in sugarcane crops in several states of Brazil. These two species were first reported in sugarcane fields in Mato Grosso do Sul in 2013. Adults were found moving on the soil, while larvae and pupae were found inside the basal internodes of sugarcane plants. S. levis is dark brown in color, with black spots on the back of the thorax and longitudinal stripes on the wings.

The species M. hemipterus has orange and black stripes, flies quickly, disperses easily, lays eggs and develops in the middle part of mature stems. The larvae also have characteristics that differentiate them, with those of M. hemipterus having an indistinct light brown spot on the first dorsal thoracic segment and those of S. levis having a distinct brown transverse line on the first dorsal thoracic segment in the shape of a “W”, next to the head and visible spiracles on the abdominal segments.

The occurrence of S. levis in sugarcane fields in areas where sugarcane cultivation is expanding may be related to the transport of seedlings that harbor larvae in the internodes at the base of the sugarcane or even adults hidden in the straw and stalks of recently cut seedlings, since this is the main way this insect spreads to areas where it does not occur. S. levis is considered a primary pest because it attacks healthy tissues at the base of the tillers or stalks, since the larvae feed by opening circular and longitudinal galleries as they develop, causing symptoms of yellowing and drying of leaves and tillers. The damage is reflected in the number, size and diameter of stalks that are final for harvest, and the economic losses can be estimated in relation to the reduction in tons of sugarcane per hectare.

Termites

Termites are insects of the order Isoptera, which has two families with important species in sugarcane cultivation (Rhinotermitidae and Termitidae). The main one is Heterotermes tenuis, which is characterized by its tapered, milky-white body, yellowish cephalic capsule, thorax with rounded sides and long mandibles. Due to its subterranean habit, H. tenuis causes great damage, as it attacks the roots of the plant and even the stalk. The damage is recognized by germination failures, in shoots, galleries in the stems and in the basal stalks of the clump. In addition to this species, Neocapritermes opacus and Procornitermes triacifer are other species of subterranean termites common in Brazilian sugarcane fields. In general, termites attack the shoots, damaging the buds, influencing the germination of the sugarcane, causing a large number of failures and, in some cases, requiring the replanting of the crop. 

Root sharpshooters

The root spittlebug Mahanarva fimbriolata (Hemiptera: Cercopidae) currently constitutes one of the most worrying phytosanitary problems in sugarcane, as it establishes itself and multiplies abundantly in areas where raw sugarcane is harvested. Benefiting from the increase in soil moisture resulting from the accumulation of straw left in the area after harvesting, the populations of this pest have increased significantly to the point of causing reductions in stalk and sugar productivity in several locations, in addition to interfering in industrial processes by introducing contaminants that hinder sugar recovery and inhibit fermentation. The damage is caused mainly by nymphs, which suck water and nutrients from the roots. Their infestation is recognized by the exudation of whitish foam similar to soap suds, which surrounds the base of the clump and serves as its protection. When adults feed on leaves, they cause necrosis of the leaf tissue at the point of insertion of the mouthparts, causing longitudinal necrosis in the leaves, which reduces the photosynthetic area. All this damage results in atrophy and thinning of the stem, with loss of sucrose and increased fiber content. Newly hatched nymphs are orange in color, becoming cream as they develop, maintaining only a few spots of the initial color. Male adults of M. fimbriolata are bright red to straw-yellow in color, with opaque to transparent forewings with longitudinal spots that reduce in width and length until they are completely absent. Females are dark brown in color with defined longitudinal spots.

The root hopper has been found more frequently in sugarcane fields where raw sugarcane is harvested mechanically. In places where sugarcane is burned before being harvested, the insect has not been detected. Burning sugarcane before harvesting is considered a form of cultural control of the leafhopper, as it allows the destruction of its biological forms (eggs, nymphs and adults), especially eggs in diapause.

Caterpillar Hipponeus taltula

This species is also known as the hairy borer and was first reported in the 1970s in Brazil attacking sugarcane. The caterpillars penetrate the stem at the base, damage this region and when the plants are very young, they cause the “dead heart” symptom. The damage is similar to that caused by weevils, causing weight loss in plants, lateral sprouting, aerial rooting, broken canes and stunted internodes. Furthermore, fungi penetrate through the holes, causing rot and a drop in industrial performance due to the inversion of sucrose, a decrease in the purity of the juice and contamination problems in the alcoholic fermentation process.

How to manage

The control of soil-associated pests in sugarcane cultivation can be carried out preventively or curatively, using chemical, biological, cultural or behavioral tactics depending on the pest in question. This control must be used rationally, based on the results of monitoring soil pests in the renovation areas, with the percentage of trenches with damaged clumps being the basis for defining the need for intervention. As a general rule, soil pests should be controlled, preferably, when preparing the soil or planting sugarcane.

Termite control has been normally carried out during sugarcane plantation reform, by spraying insecticides in the planting furrow, with fipronil being the most commonly used. Some studies have shown the viability of biological termite control using baits impregnated with the fungus Beauveria bassiana. Migdolus control should be carried out during the plowing and subsoiling operations, applying pesticides in depth or even on the seedlings in the planting furrow, forming a chemical barrier to protect the stems. The sexual pheromone of Migdolus sp. can also be an important tool for monitoring and controlling this species, using one trap per 20- to XNUMX-hectare plot between the months of October and March and replacing the septa every three to four weeks. Capturing a large number of males in pheromone traps reduces mating and reduces the next generation of the pest in the sugarcane area.

Control of the weevil Sphenophorus levis in sugarcane fields can be achieved through chemical, cultural and biological tactics. Chemical control is usually implemented through the application of insecticides in the planting furrow or through toxic baits for adults, consisting of sugarcane stalks soaked in an insecticide solution. Cultural control of S. levis is achieved by using healthy seedlings at planting, i.e., without the presence of the pest. The movement of contaminated seedlings is the most likely hypothesis to explain the rapid expansion of the pest in sugarcane fields, since the insect practically does not fly and moves slowly. The mechanical destruction of ratoons in areas with high infestation of the pest is also another important strategy for controlling the weevil, since there is specific equipment for this purpose in sugarcane mills. In addition, several studies in the literature demonstrate the possibility of biological control of the sugarcane weevil using entomopathogenic fungi and nematodes.

The sugarcane leafhopper, Mahanarva fimbriolata, is normally controlled by fire in areas where sugarcane is harvested manually. In mills where sugarcane is harvested mechanically and where this pest is a problem, control has been successfully achieved using the fungus Metarhizium anisopliae or even chemical insecticides applied to the crop line, using a method called ratoon cutting, when more than three nymphs are observed per linear meter in the sugarcane row. Biological control with the fungus has been widely used because it is economical and does not harm the environment.

Corós and the hairy borer can be controlled by applying insecticides in the planting furrow. However, there are practically no control evaluation studies for these two pests in sugarcane crops.

By Credit José Ávila (Embrapa Agriculture West); Gleicieli Caparróz Moraes (Federal University of Grande Dourados); and Viviane Santos (Embrapa Agriculture West)

Article published in issue 197 of Cultivar Grandes Culturas