​How to control leafhoppers in sugarcane

Sugarcane is the most important crop in Brazil when it comes to the production of sugar and biofuel, in this case ethanol. With practically 8,5 million hectares planted in the country, sugarcane is responsible for the greatest development of agribusiness involving ethanol and energy in general. However, like all agricultural crops, it is attacked by pests that cause damage from the aerial part to the roots.

Harvesting without burning has been a reality throughout the state of São Paulo for at least ten years. Despite the extension of the deadline for the total stoppage of burning having been extended until 2014, the plants are still obliged to gradually reduce the area burned each year.

Along with mechanized harvesting and without burning, attacks by the sugarcane leafhopper are increasingly frequent and intense, causing losses that can reach 60% in agricultural productivity and in the industrial quality of the raw material, through contamination with bacteria, loss of Pol and more.

Following the example of the Northeast region, biological control with the fungus Metarhikum anisopliae It also developed in crops in São Paulo and reaches an area of ​​approximately 350 thousand hectares, with tractor and aerial applications, concentrations varying between 6kg/ha and 10kg/ha, depending on the leafhopper population and variety.

Mahanarva fimbriolata

The root sharpshooter, Mahanarva fimbriolata, is considered one of the most important pests of sugarcane in the state of São Paulo and Northeast Brazil.

The nymphs, when feeding, cause "physiological disorder" as a result of their bites which, when they reach the woody vessels of the root, deteriorate it, preventing or hindering the flow of water and nutrients. The death of roots causes imbalances in the plant's physiology, characterized by dehydration of the phloem and xylem, which will give the stem hollow characteristics, thinning and the subsequent appearance of wrinkles on the external surface. Adults, when injecting toxins, produce small yellow spots on the leaves that later become reddish and, finally, opaque, significantly reducing the photosynthesis capacity of the leaves and the sucrose content of the stem. Tissue perforations by infected stylets cause contamination by microorganisms in the nutritive liquid, causing tissue deterioration at the growth points of the culm and, gradually, from the lower internodes to the underground roots. Aqueous decay presents dark colors starting at the tip of the sugarcane and can cause the death of the stalk.

In São Paulo, the life cycle of M. fimbriolata It starts in September, normally with the beginning of the rainy season. The first generation of nymphs is small due to the diapause of the eggs, but with sufficient capacity to develop until adulthood, when the laying of the second generation of nymphs begins, generally between December and January, when humidity and photoperiod are bigger. The second generation is responsible for most of the damage, which will only appear in February and March, when there is the third generation of nymphs, which will develop into adulthood, however, in smaller numbers than the previous generation and will lay eggs. which will enter diapause from April, when the photoperiod and humidity decrease.

The prohibition of burning sugar cane in the state of São Paulo, through State Decree-Law no.^o 42.056/97, has caused changes in the management of this crop, due to the increase in the area harvested without burning and, as a consequence, in many regions there have been increases in the root sharpshooter population.

The sugarcane leafhopper has become a serious problem in some regions of São Paulo, such as Ribeirão Preto, São José do Rio Preto, Araras, Andradina and Araçatuba, where the majority of sugarcane is already harvested mechanically and raw, as there is no burning of the straw, this material accumulates in the soil and increases humidity, thus facilitating the growth and spread of the sugarcane leafhopper, M. fimbriolata. And considering that with the new environmental legislation São Paulo will prohibit the burning of sugarcane, a significant increase in the sugarcane population is expected. M. fimbriolata causing serious damage to plants and suppliers, in addition to increasing costs to control this pest.

Control

The root hopper control strategy begins with monitoring the pest, which must be carried out at the beginning of the rainy season and throughout the infestation period, so that the evolution or control of the pest can be monitored. The economic damage level (NDE) is 20 nymphs/linear meter of furrow and 1 adult/cane; the control level (NC) is two – four nymphs/meter and 0,5 adult/reed to 0,75 adult/reed.

Monitoring is essential to decide on the pest control strategy, and detection of the first generation allows more efficient control, mainly through the fungus Metarhikum anisopliae. However, in the case of applying the fungus, the control level to be considered is one nymph per linear meter or when observing the first nymphs attacking the sugarcane in the months of September or October, due to the slowness of biological control.

The variety and cutting season are other important parameters to be analyzed in the integrated management of sugarcane root sharpshooter. Insect attack can affect the industrial quality of sugarcane and this effect tends to be different according to the variety, which may be more preferred and/or resistant, which interferes with planting, harvesting time and the control system at hand. be adopted. The damage caused by the leafhopper can be high for many varieties, such as: RB 72-454, RB 82-5336, RB 83-5486, SP 80-1842 and IAC 82-2396.

Biological control

Biological control with microorganisms is one of the main components of integrated leafhopper management. Biological control is non-polluting, does not cause biological imbalances, is long-lasting and takes advantage of the biotic potential of the agroecosystem, is not toxic to humans and animals and can be applied with conventional machines, with small adaptations.

The development of the fungus M. anisopliae on the leafhopper, it occurs as follows: the conidia germinate and penetrate the insect's integument over a period of two to three days. The colonization period occurs from two days to four days and sporulation takes two days to three days, depending on environmental conditions. The total cycle of the disease is eight days to ten days.

In the Alagoas region, during the 1977 to 1991 M. anisopliae was sprayed on approximately 670 thousand hectares of sugarcane infested by the leafhopper, M. posticata, resulting in a reduction of approximately 72% in the rates of manifestation of this pest. Initially, the area treated with chemical insecticide was 150 thousand ha/year. In Pernambuco, 38 tons of fungus conidia were applied. The time of application of the fungus coincides with the rainy season, July and August, in Northeast Brazil. The application interval was 30 days, ideally for the application to coincide with the period of greatest transit of the nymphs in the culms. The strategy in this case was to increase, since the pathogen was in the area. From 200g of pure conidia/ha to 500g of pure conidia/ha are recommended. Land applications must be made with atomizers, with water consumption of 50L/ha to 200L/ha. In aerial applications, 20L/ha to 30L/ha are used, two to five meters above the sugarcane level.

The Biological Institute (IB/Apta/SAA-SP) developed biological control research on M. fimbriolata with the fungus Metarhikum anisopliae. The thematic project, financed by the São Paulo State Research Support Foundation (Fapesp) coordinated by IB, was in partnership with Esalq USP and UFSCar - Araras-SP.

Main recommendations for applying the fungus M. anisopliae (Frame)

- Start tractor applications with a directed jet with 0,5 to 1 nymph/linear meter using the concentration of 2 to 3 x 1012 conidia/ha (approximately 2kg to 3kg rice + fungus/ha) from October onwards.

- Reapply 2 to 3 x 1012 conidia/ha in December or January in early or preferred varieties.

- Above five nymphs/linear meter apply 1 x 1013 conidia/ha (10kg rice+fungus/ha) from December.

- Granular aerial application use 8 x 1012 to 1 x 1013 conidia/ha (8kg to 10kg rice + fungus/ha).

- Liquid aerial application use 5 x 1012 conidia/ha. (5kg rice + fungus/ha)

Em Operação with tractor the fungus must be applied at a flow rate of 200 liters of water/ha to 300 liters of water/ha, using herbicide nozzles with fan jets and pendant jets, with the jet directed towards the sugarcane stump, preferably after 16pm to avoid the high incidence of ultraviolet rays, reaching until dawn, a period in which the relative humidity is high and the temperature is cooler, facilitating microbial control of the fungus.

Aerial application can be used with a flow rate of 40 liters/ha to 50 liters/ha, with large drops and a crop height of two meters.

Final considerations

Using integrated pest monitoring and management techniques, it will be possible to live with the sugarcane leafhopper in the state of São Paulo, applying a microbial control program with fungus and, in the case of overpopulations, the application rational use of natural or chemical pesticides, to balance the population, preserving other natural enemies of the pest, such as predatory flies Salpingogaster nigra and the fungus Batkoa apiculata.

Click here to read the article in Revista Cultivar Grandes Culturas, issue 177.