Influência da chuva na eficácia de Bacillus thuringiensis associado a adjuvantes no controle de Spodoptera frugiperda em algodão
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2019-12-06
Autores
Santos, Cicero Antonio Mariano dos
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Universidade Estadual Paulista (Unesp)
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O algodão (Gossypium hirsutum L.) tem grande relevância para a economia mundial. Dentre os principiais fatores limitantes da produção estão os problemas fitossanitários, que ocorrem em todas as fases da cultura. O inseto Spodoptera frugiperda (JE Smith) (Lepidoptera: Noctuidae) é importante devido a sua capacidade de causar danos nas folhas e maçãs do algodoeiro, muitas vezes requerendo a aplicação frequente de inseticidas para o seu controle. Em geral são utilizados inseticidas químicos. Entretanto, o uso de bioinseticidas têm aumentado consistentemente, principalmente aqueles à base de Bacillus thuringiensis, chamados de Bt bioinseticidas. Fatores abióticos como a chuva também interferem na eficiência de aplicações de Bt bioinseticidas e consequentemente no controle do organismo alvo. Uma alternativa que pode dar proteção ao Bt mediante chuva é a adição de adjuvantes a calda. Porém, pouco se sabe o quanto a associação do Bt com adjuvantes afeta no crescimento vegetativo, esporulação e persistência da bactéria e o controle. Portanto é de extrema importância à compreensão das interações físico-químicas e biológicas da mistura de Bt bioinseticidas e adjuvantes. Neste contexto, objetivou-se avaliar o efeito da adição de adjuvantes nas características físico-química e biológicas dos Bt bioinseticidas nas formulações Dipel® WP e Dipel® SC submetidas à chuva artificial para o controle de S. frugiperda em plantas de algodão. Para simular a chuva, foram utilizadas as lâminas de chuva artificial de 20mm aplicada uma hora após a aplicação dos tratamentos e os tratamentos controle sem chuva. Para a avaliação de contagem de esporos com e sem efeito de chuva, foram utilizados como amostradores, uma disco foliar da parte mediana da planta. Para efeito de controle dos tratamentos, discos foliares de 10,25 cm2 foram oferecidos a lagartas até segundo instar de S. frugiperda. A mortalidade larval foi registada até 96 horas do início do experimento para cada período avaliado. Para avaliação dos parâmetros biológicos de Bt bioinseticidas e adjuvantes foram realizados testes de compatibilidade biológica, aferindo o crescimento vegetativo das colônias, esporulação e testes de eficiência de controle de S. frugiperda com suspenções de Bt nas concentrações de 106 e 3x108 obtidas das raspagens das colônias. Por fim, foram determinadas características de espectro de tamanho de gotas das caldas, tensão superficial, ângulo de contato e estabilidade de calda, pH e condutividade elétrica. Em relação aos parâmetros físico-químicos da mistura das formulações Dipel® WP e Dipel® SC e adjuvantes, os maiores tamanho de gotas e menor susceptibilidade à deriva foram observadas nas caldas da formulação WP, apresentando também os menores ângulos de contato e tensão superficial de gotas. A adição do adjuvante LI acarretou menores valores de pH e maiores de condutividade elétrica em todos os períodos de descanso avaliados. Nos testes de compatibilidade biológica, foi observado o maior crescimento vegetativo de colônias, números de esporos e mortalidade de S. frugiperda na associação de LI e Bt bioinseticidas. A aplicação de chuva artificial proporcionou uma redução de até 50% no número de esporos e controle de S. frugiperda. A adição do adjuvante LI nas caldas de Bt bioinseticidas proporcionou em maiores quantidades de esporos e controle de S. frugiperda. A persistência de esporos e controle de S. frugiperda é afetada 24 horas após a aplicação dos Bt bioinseticidas associados ou não a adjuvantes. Nos testes de persistência de esporos e controle em condições de campo, as caldas Bt bioinseticidas com adição do LI e Bt bioinseticidas isoladas proporcionaram as maiores quantidades de esporos e controle de S. frugiperda desde 1 hora após a aplicação dos tratamentos à 72 horas após a aplicação das caldas, porém foi observado uma redução gradativa na contagem de esporos e taxa de controle no decorrer do tempo de avaliação.
Cotton (Gossypium hirsutum L.) has great relevance to the world economy. Among the main limiting factors of production are the phytosanitary problems that occur at all stages of the crop. The insect Spodoptera frugiperda (JE Smith) (Lepidoptera: Noctuidae) is important because of its ability to cause damage to cotton leaves and apples, often requiring insecticides to be applied frequently for its control. In general, chemical insecticides are used. However, the use of bioinsecticides has consistently increased, especially those based on Bacillus thuringiensis, called Bt bioinsecticides. Abiotic factors such as rain also interfere with the efficiency of Bt applications and consequently in the control of the target organism. An alternative that can protect Bt in the rain is the addition of adjuvants to the syrup. However, little is known about how the association of Bt with adjuvants affects vegetative growth, sporulation and bacterial persistence and control. Therefore, it is extremely important to understand the physicochemical and biological interactions of the mixture of Bt bioinsecticides and adjuvants. In this context, the objective of this study was to evaluate the effect of the addition of adjuvants on the physicochemical and biological characteristics of Bt bioinsecticides in the formulations Dipel® WP and Dipel® SC submitted to artificial rain to control S. frugiperda in cotton plants. To simulate the rain, the 20mm artificial rain blades applied one hour after the application of the treatments and the control treatments without rain were used. For the evaluation of spore count with and without rain effect, a leaf disc of the middle part of the plant was used as samplers. For treatment control purposes, leaf disks of 10.25 cm2 were offered to caterpillars up to the second instar of S. frugiperda. Larval mortality was recorded up to 96 hours from the start of the experiment for each period evaluated. Biological compatibility tests were performed to evaluate the biological parameters of Bt bioinsecticides and adjuvants, measuring the vegetative growth of the colonies, sporulation and control efficiency tests of S. frugiperda with Bt suspensions at 106 and 3x108 concentrations obtained from colony scraping. Finally, the characteristics of the droplet size spectrum, surface tension, contact angle and spray stability, pH and electrical conductivity were determined. Regarding the physicochemical parameters of the mixture of formulations Dipel® WP and Dipel® SC and adjuvants, the largest droplet size and lower susceptibility to drift were observed in the WP formulation mixtures, also presenting the lowest contact angles and surface tension of the droplets. Addition of LI adjuvant resulted in lower pH values and higher electrical conductivity in all rest periods evaluated. In the biological compatibility tests, the highest vegetative growth of colonies, spore numbers and mortality of S. frugiperda was observed in the association of LI and Bt bioinsecticides. The application of artificial rain provided a reduction of up to 50% in the number of spores and control of S. frugiperda. Addition of L1 adjuvant to Bt bioinsecticide spray provided greater spore and control of S. frugiperda. Spore persistence and control of S. frugiperda is affected 24 hours after application of Bt bioinsecticides with or without adjuvants. In spore persistence tests and control under field conditions, Bt bioinsecticides with addition of LI and Bt isolated bioinsecticides provided the highest spore and S. frugiperda control levels for 1 hour after treatment application at 72 hours after treatment. However, a gradual reduction in the spore count and control rate was observed over the evaluation time.
Cotton (Gossypium hirsutum L.) has great relevance to the world economy. Among the main limiting factors of production are the phytosanitary problems that occur at all stages of the crop. The insect Spodoptera frugiperda (JE Smith) (Lepidoptera: Noctuidae) is important because of its ability to cause damage to cotton leaves and apples, often requiring insecticides to be applied frequently for its control. In general, chemical insecticides are used. However, the use of bioinsecticides has consistently increased, especially those based on Bacillus thuringiensis, called Bt bioinsecticides. Abiotic factors such as rain also interfere with the efficiency of Bt applications and consequently in the control of the target organism. An alternative that can protect Bt in the rain is the addition of adjuvants to the syrup. However, little is known about how the association of Bt with adjuvants affects vegetative growth, sporulation and bacterial persistence and control. Therefore, it is extremely important to understand the physicochemical and biological interactions of the mixture of Bt bioinsecticides and adjuvants. In this context, the objective of this study was to evaluate the effect of the addition of adjuvants on the physicochemical and biological characteristics of Bt bioinsecticides in the formulations Dipel® WP and Dipel® SC submitted to artificial rain to control S. frugiperda in cotton plants. To simulate the rain, the 20mm artificial rain blades applied one hour after the application of the treatments and the control treatments without rain were used. For the evaluation of spore count with and without rain effect, a leaf disc of the middle part of the plant was used as samplers. For treatment control purposes, leaf disks of 10.25 cm2 were offered to caterpillars up to the second instar of S. frugiperda. Larval mortality was recorded up to 96 hours from the start of the experiment for each period evaluated. Biological compatibility tests were performed to evaluate the biological parameters of Bt bioinsecticides and adjuvants, measuring the vegetative growth of the colonies, sporulation and control efficiency tests of S. frugiperda with Bt suspensions at 106 and 3x108 concentrations obtained from colony scraping. Finally, the characteristics of the droplet size spectrum, surface tension, contact angle and spray stability, pH and electrical conductivity were determined. Regarding the physicochemical parameters of the mixture of formulations Dipel® WP and Dipel® SC and adjuvants, the largest droplet size and lower susceptibility to drift were observed in the WP formulation mixtures, also presenting the lowest contact angles and surface tension of the droplets. Addition of LI adjuvant resulted in lower pH values and higher electrical conductivity in all rest periods evaluated. In the biological compatibility tests, the highest vegetative growth of colonies, spore numbers and mortality of S. frugiperda was observed in the association of LI and Bt bioinsecticides. The application of artificial rain provided a reduction of up to 50% in the number of spores and control of S. frugiperda. Addition of L1 adjuvant to Bt bioinsecticide spray provided greater spore and control of S. frugiperda. Spore persistence and control of S. frugiperda is affected 24 hours after application of Bt bioinsecticides with or without adjuvants. In spore persistence tests and control under field conditions, Bt bioinsecticides with addition of LI and Bt isolated bioinsecticides provided the highest spore and S. frugiperda control levels for 1 hour after treatment application at 72 hours after treatment. However, a gradual reduction in the spore count and control rate was observed over the evaluation time.
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Palavras-chave
Bt bioinseticidas, Controle microbiano, MIP, Mistura em tanque, Bt bioinsecticides, Microbial control, Tank mix