Sugarcane borer control measures

Despite all the positive prognoses and as occurs with crops of economic importance, sugar cane is attacked by numerous pests, with emphasis on the sugar cane borer, Diatraea saccharalis. This is an extremely harmful pest to sugarcane, capable of decimating entire sugarcane fields if appropriate control measures are not taken.

The increase in pest infestation in sugarcane fields is linked to climatic factors, large areas of expansion, planting of susceptible varieties, increase in fertigated areas and mainly due to neglect of the details that make up the Integrated Management of this pest.

Description and biology

The complete biological cycle, from egg to adult, of the sugarcane borer D. saccharalis It lasts around two months, with up to six generations per year, depending on climatic conditions.

Females oviposit on leaves, preferably on the dorsal surface. Each clutch can contain from five to 50 eggs, grouped similar to fish scales. The average fecundity of this species is approximately 400 eggs. Initially, the eggs are yellow, with embryonic development they turn orange and, later, the cephalic capsule of the caterpillar is visible still inside the egg. Six days after laying, if the eggs are fertile, the caterpillars hatch).

The newly hatched caterpillars are white in color, becoming cream in color as they develop, with some dark spots spread across the body. They initially feed on the leaf parenchyma, inside the leaf sheath; After the first ecdysis, they penetrate the softest part of the stem and, piercing it, open galleries from the bottom to the top. These galleries can be of two forms: longitudinal, in most cases, and, sometimes, transversal. They go through six instars, over an average period of 28 days, depending on weather conditions. The caterpillar about to transform into a pupa stops feeding, cleans and enlarges the gallery where it developed, opens a hole to the outside, closes it with silk threads and sawdust and transforms into a chrysalis. It is brown in color and lasts eight days, the time varying according to the weather conditions. Measures approximately 16mm to 20mm in length.

The adults of D. saccharalis They are straw yellow, with dark spots on the forewings, the hindwings are whitish, measuring approximately 25mm in wingspan. They have a lifespan of approximately eight days, are nocturnal and hide during the day. Oviposition occurs mainly at the beginning of dusk.

Population fluctuation

In general, the cycle D. saccharalis begins in September-October, normally, after the emergence of adults from the winter generation in the region. These adults generally look for new reeds to carry out their postures. The second generation occurs between December and February; the third between February and April, and in May and June the fourth generation begins, which can last for a few months.

Losses

The caterpillars cause direct damage, by opening galleries, causing weight loss in the sugarcane and which can lead the plant to death, “dead heart”, especially in new canes. When they make circular (transverse) galleries, they section the culm, causing it to break due to the action of winds. Aerial rooting and lateral shoots also occur due to its attack.

The indirect losses are considerable, since, through holes and galleries, fungi penetrate that cause red rot of the culm, which can cover the entire region between the different galleries. The fungi that cause red rot, Colletotrichum falcatum e Fusarium subglutinans, invert the sucrose, reducing the purity of the juice and the industrial yield in the sugar and/or alcohol production process. In the case of sugarcane intended only for the production of alcohol, the microorganisms that contaminate the juice compete with yeast in the alcoholic fermentation process, reducing the yield.

For every 1% of the Final Infestation Intensity Index caused by the pest (number of internodes attacked by the borer/red rot complex), losses of 1,14% occur in sugarcane production (TCH) and a further 0,42% in production of sugar or 0,25% in alcohol production. 

Sampling via trap

Currently, pheromone-based traps, through the use of virgin females, have been the basis in detection, population monitoring and control programs. D. saccharalis in all sugarcane producing regions.

When choosing to use this tool, it is essential to know the bioecological and behavioral aspects of this pest, as it will then be possible to properly interpret the information from the assessments, in addition to determining how the population is distributed in the area.

According to the oviposition habit of D. saccharalis, these traps must be installed in the canopy region, this way, they follow the height of the plant throughout its development. By joining the leaves of parallel plants, and subsequently tying them, this trap is then positioned between the crop row. Knowing that 74% of adults fly within a radius of 200 meters, which makes up an area of ​​12,5 hectares, it is recommended to size a trap for up to 50 hectares.

The "sexual attractant" is made up of three virgin females and three more female pupae from the same batch, thus making a total of six biological forms, which will be imprisoned in a "bob" type cage and placed inside the trap.

In the field, at the time of installation, the organization of traps through nominal identification is essential, as is their geographic location. This planning is the basis for the high operational performance that this operation requires, as well as necessary for mapping the information collected. These traps must be installed within the area to be sampled, on the edge of the carriers.

The traps must be read three nights after their installation, noting the number of males captured in each trap. The control level determined for this pest is ³ six males/trap in 30% of the total number of traps.

The sampling frequency in the wet season is fortnightly, thus positioning chemical and biological control (cotesia flavipes). In the dry season, monitoring is monthly, placing only biological control through the release of C. flavipes.

During the humid period, two control methods are used - chemical and biological (C. flavipes) - and chemical control must be carried out six days after verifying the level of control, and 14 days after this spraying, four cups of 1.500 wasps of C. flavipes per hectare. Outside this period, for the same level of control, only four cups of 1.500 wasps are released. C. flavipes per hectare after 20 days of evaluating these traps, based on the same percentage (30% of the total number of traps).

control methods

The control strategy must take into account the plant's phenology, the varieties most susceptible to attack, the nurseries, the irrigated areas and mainly the productive potential, for future decision-making planning.

Cultural control

In the Integrated Management of this pest, the planting of resistant varieties, the cutting of sugarcane without topping, rapid grinding, the elimination of host plants in the vicinity of the sugarcane field, mainly corn, millet and sorghum, after harvesting, are effective measures to reduce the pest population.

Biological control

There are several natural enemies capable of controlling the pest.

predators

 They are responsible - naturally - for eliminating a significant portion, mainly of eggs and newly hatched caterpillars. Ants, belonging to genera such as Solenopsis sp. Pheidole sp. Camponotus sp., among others, form the main contingent, being complemented by coleopterans, neuropterans and dermapterans. In some locations, more than 90% of the initial pest population is controlled by this complex of natural enemies.

Caterpillar parasitoid

The wasp C. flavipes was introduced in Brazil in 1974 and has stood out in several places as extremely efficient in controlling D. saccharalis. It has advantages due to the ease of multiplication in the laboratory in relation to the Lydella minense and Paratheresia claripalpis flies that were previously used.

chemical control

 This control method must be seen as a priority tool to be used in situations that require a quick and efficient control response, under the risk of not having it, greatly aggravating the losses. This tool must be analyzed with great care, especially the characteristics of each chemical molecule and its control potential.

Final Infestation Intensity Index

Sampling for the Final Infestation Intensity Index (Final I.I.I.) is carried out by collecting sugarcane stalks at the time of harvest. In the field, four points must be sampled at random, represented by five culms each, taken at random, totaling 20 culms evaluated. To calculate the I.I.I. Finally, each of the collected culms is opened longitudinally, counting the number of internodes and those that are damaged by the borer/red rot complex. The data obtained is applied to the formula:

Once the Final Infestation Intensity Index has been determined, there are different degrees of infestation, Acceptable (≤ 1,0); Low (1,1 to 3,0); Medium (3,1 to 6,0); High (6,1 to 9,0) and unacceptable (³ 9,1), these values ​​being expressed as a percentage.

The closing thought

Once D. saccharalis is an insect pest capable of causing enormous damage to sugarcane crops, it is necessary to carry out management planning that integrates several control measures, such as ethological, cultural, biological and chemical. All of these control measures must be carried out throughout the year, according to the appropriate climatic conditions for each of them. The use of pheromone traps is an essential tool in decision-making, especially for carrying out chemical and biological controls and, consequently, reducing the damage caused by this pest. It is also important to highlight that management to control this pest must be regionalized and not punctual, requiring joint action from everyone. Collective management is the fundamental point for success in combating D. saccharalis.

José Francisco Garcia, Global Cana - Entomological Solutions

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