Integrated management of boll weevil in sugarcane

Important and difficult to control pest, Sphenophorus levis is capable of seriously compromising the productivity and longevity of sugarcane fields. The adoption of integrated management and the search for new combat alternatives are necessary to face this great challenge.

Sphenophorus levis (Coleoptera: Curculionidae), is an important pest in sugarcane. The larvae of this insects destroy the plant's rhizome, as they cause damage of around 30 tons of sugarcane per hectare, in addition to reducing the longevity of the sugarcane field. That insect is found throughout practically all sugarcane areas, mainly in São Paulo, causing losses of up to 60% in tons of sugarcane per hectare, causing tiller death. The damages are caused by larvae that shelter inside the rhizome and damage the fabrics. This can result in the death of the plant and failure of the shoots. ratoons, with losses of up to 30 tons of sugarcane/ha/year. The repeated attacks on ratoon areas and the consequent reduction in the crop’s “stand” cause cumulative losses in cuts, forcing early reforms in the sugarcane field, which they often do not make it past the second cut (Gallo et al. 2002).

It is not possible to control the cane weevil with a single strategy. Integrated management, through various management practices, control, allows a balance of the pest population to be achieved and a “coexistence”, since it will no longer be possible to eliminate this insect from Agriculture. Therefore, prevention through inspection of sugarcane seedlings before planting, as well as knowledge of the origin of these seedlings, from an area not infested, it is essential to prevent the spread of S. levis.

 Monitoring the insect in the adult stage is the beginning of management, as without knowledge of the pest, as well as its index population, it is not possible to apply control practices correctly. That Monitoring is carried out with traps made from sugarcane billets. 0,5 meter, cut in half. Billet traps are placed at the bases of the tussocks and covered with sugarcane straw at the rate of 100 totes for each hectare. After 20 days, the assessment of adult incidence is made based on the number of insects dead (Almeida, 2005).

The main control methods, as soon as if you are aware of the pest in the crop, they are: destruction of ratoons, control biological and chemical control with toxic baits.

The destruction mechanics of the ratoons during the planting period, when the renovation of the sugarcane plantation, is the most used method to control the sugarcane weevil, as it aims to The objective is to expose the larvae to their predators as much as possible. However, this practice presents satisfactory results only in the first cut, as many larvae can survive by feeding on organic matter left in the field, after the destruction of the ratoons, without also affecting the adult forms of the insect (Almeida, 2005).

The use of Toxic baits can be employed in keeping the destroyed area free of host vegetation for a period of more than 3 months and in planting with application of fipronil 800 WG (250 g/ha). However, despite all these measures, there is an increase in pest populations, with frequent records of new infested areas. This demonstrates the difficulty of controlling this insect, highlighting the importance of continuing research in the search for more effective alternatives (Leite et al., 2006).

The baits toxic substances are still very common in the countryside. Research was carried out to improve the attraction of adults from S. levis, (Giron-Pérez et al., 2009). These authors found that the sugarcane internodes mixed with 10% molasses and fermented for 24 hours and 48 hours were highly attractive to S. levis, outperforming other substrates such as pineapple peel + molasses or water, and sugarcane + water.

Biological control can also be a important control strategy, but adjustments are still needed for the use of entomopathogenic microorganisms, or even entomophagous insects.

The beginning of microbial control of S. levis occurred through the selection of isolated from M. anisopliae (ESALQ 259) It is B. bassina (ESALQ 447), at Esalq/USP in 1990 (Badilla & Alves 1991).

Selection surveys were carried out isolated from entomopathogenic nematodes, where Steinernema Brazilian IBCBn 06 was the most virulent. The application of entomopathogenic nematodes in field was also studied, producing satisfactory results in controlling S. levis, which can be applied in a combined with fungi. The Biological Institute, in partnership with the Center for Sugarcane Technology (CTC) and the Federal University of São Carlos (UFSCar), carried out research on nematodes Heterorhabditis indicates e S. brazilense and fungi entomopathogenic, M. anisopliae e B. bassiana. In a greenhouse, S. brazilense caused mortality above 70% of larvae within the plant's rhizome, at a dosage of 1x108 juveniles infectives/ha (Tavares et al. 2007). Under field conditions, the application of nematodes provided more than 60% of adult mortality and produced gains of 17 tons/ha of sugar cane (Leite et al. 2012).

Likewise, the nematode association with the chemical insecticide thiamethoxam 250 WG also provided weight gains of sugarcane of up to 28 tons/ha, where the nematode was applied with a sub-dosage of 500 g thiamethoxam 250 WG/ha (Leite et. al. 2012).

The isolate IBCBn 06 from S. braziliense is produced by the company BioControle Methods of Pest Control, from Indaiatuba, São Paulo, with registration at the Ministry of Agriculture and Livestock  (Map) with recommended dosage of 1 kg/ha in 400 liters of water (terrestrial application) (BRAZIL, 2015).

Simi (2014) selected the IBCB 383 isolates from M. anisopliae and IBCB 170 of B. bassiana to S. levis, isolated from the Institute Biological. It was observed that in the combined application the nematode S. braziliense, under field conditions, the effect with M. anisopliae was antagonistic and B. bassiana synergistic in mortality of larvae of Galleria mellonella.

To use the fungus, the strategy used is application of 500 g of conidia/ha on baits made from sugar cane stalks, split lengthwise and impregnated with fungal conidia, distributing 200 baits per hectare. Adult insects are attracted to bait, become contaminated with the applied fungus and die on or near the bait, spreading the disease in the area, due to the high density of baits. This strategy is interesting to be applied during the autumn – winter period, when there is a decrease in adults in the crop. The application of 1013 conidia/ha with rice + fungus or sprayed, can also be carried out during the spring – summer period, mainly from November to March, when there is greater adult traffic on the farm. With the integration of these fungus application techniques B. bassiana, an adult parasitism rate of 75% has been observed (J. E. M. Almeida, personal communication).

O integrated pest management is the best way to control S. levis in sugar cane. However, research is needed with new methods of cultural control, new chemical molecules and/or alternatives for application in crops, in addition to controlling biological with nematodes and entomopathogenic microorganisms. If there is not a joint application of these measures, the cane weevil will continue to be a major challenge for the crop, causing enormous losses in sugar production and ethanol, as it is a difficult pest to control.

Article published in issue 219 of Cultivar Grandes Culturas, August, 2017.