Leonardo D. B. da Silva

Monitoring the susceptibility to insecticides in Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) populations from Brazil

Monitoring the susceptibility of a pest population to pesticides is essential for resistance management programs. The objective of this research was to evaluate the genetic variability in pesticide susceptibility in populations of Bemisia tabaci (Gennadius) collected from different Brazilian agricultural regions through the use of two different tests. Four whitefly populations, two from Goiás state (GO-1 and GO-2) e two from Bahia state (BA-1 and BA-2), were tested against a susceptible reference one (SusIAC). A residual contact bioassay was used to evaluate the pesticide susceptibility of each population by using diagnostic concentration bioassays and by estimating the baseline susceptibility data to each one of the tested insecticides, acetamiprid, imidacloprid, thiamethoxam, chlorpyrifos and endosulfan. Adult insects of unknown age and sex were tested. Evaluations were performed after 24h for endosulfan and 48 h for the other chemicals. Both procedures showed significant differences in the susceptibility to the pesticides among B. tabaci populations. However, the discrimination among B. tabaci populations was more evident with the use of diagnosis tests. The population GO-2 was significantly less susceptible to the tested pesticides than SusIAC, mainly to neonicotinoids. The most critical resistance situation of B. tabaci was detected to thiamethoxam, followed by imidacloprid.

Eficiência de Azadiractina no controle de mosca-branca em meloeiro sob condições de casa de vegetação e de campo

Melons are of great importance for exportation by the Brazilian northeast region, actually being threatened by the whitefly pest, which is only controlled by the use of the conventional chemical insecticides actually used in the crop. In this study a potential botanical insecticide containing 1% Azadirachtin was evaluated against Bemisia argentifolii on melon, under greenhouse and field conditions. A randomized complete block design was used in both cases, with four replicates. Evaluating nymphs in greenhouse and nymphs and adults in field, we observed an increase in mortality by increasing dosages. In field, efficiency was 67.83 and 70.13% for adults and 80.36 and 88.10% for nymphs using 4.0 and 8.0 ml/L of the commercial Azadirachtin formulation, respectively.

Efeito de derivados de nim aplicados por pulverização sobre a mosca-branca em meloeiro

A mosca-branca e uma das principais pragas do meloeiro na regiao Nordeste do Brasil. Estudou-se neste trabalho o efeito de extratos aquosos de folhas e de sementes de nim (Azadirachta indica A. Juss.) e uma formulacao a base de azadiractina comparados com o inseticida buprofezin, aplicados por pulverizacao, sobre ninfas da mosca-branca, Bemisia tabaci biotipo B, em melao cv. Torreon, sob condicoes de casa de vegetacao. Tres experimentos independentes foram realizados no delineamento inteiramente casualizado, com sete tratamentos e numero variavel de cinco a sete repeticoes. Cada planta constituiu uma unidade experimental. No primeiro experimento, os tratamentos foram: testemunha absoluta (agua), Neemazal® (1,2% de azadiractina) nas doses 12; 24; 48; 96 e 192 ppm de azadiractina. No segundo: testemunha absoluta (agua), extrato de semente a 1; 2; 4; 8 e 16 g/100ml. No terceiro, o extrato de folhas foi aplicado nas mesmas proporcoes que o de sementes. Para cada experimento aplicou-se como testemunha positiva, o produto comercial Applaud® (buprofezin) na dose de 1,5g. p.c./L, que corresponde a 0,375 g de ingrediente ativo(i.a)/L de calda. A azadiractina foi eficiente em todas as doses causando reducao de ate 98% na media de ninfas vivas. Quando aplicado acima de 24 ppm, este composto apresentou desempenho semelhante ao inseticida padrao buprofezin. Os extratos de sementes a 1; 2; 4; 8 e 16g/100 ml reduziram significativamente a media de ninfas vivas, nao diferindo da acao do inseticida padrao. Os extratos de folha nao foram eficientes no controle de ninfas.

Evapotranspiração e coeficientes de cultivo da beterraba orgânica sob cobertura morta de leguminosa e gramínea

As praticas agricolas que maximizam a produtividade e o uso da agua sao de vital importância para a agricultura. Assim, foram testados tres tipos de manejo do solo com objetivo de determinar a evapotranspiracao (ETc) e os coeficientes de cultivo (kc) da beterraba. Os tipos de manejo foram a utilizacao de coberturas mortas vegetais, denominadas capim cameroon (Pennisetum purpureum), gliricidia (Gliricidia sepium) e solo sem cobertura morta em area experimental do SIPA (Sistema Integrado de Producao Orgânica) localizado em Seropedica, Brasil. A lâmina de irrigacao foi estimada com base no balanco de agua no solo, cujo monitoramento foi realizado com a tecnica da TDR. As ETc acumuladas para a cultura da beterraba foram 59,41; 55,31 e 119,62 mm, respectivamente, para capim cameroon, gliricidia e solo sem cobertura morta. A evapotranspiracao de referencia (ETo) foi obtida por meio do modelo de Penamn-Monteith. Os valores medios de kc obtidos para as fases inicial, media e final de desenvolvimento foram de 0,39; 0,42 e 1,02; 0,79; 0,76 e 1,18; e 0,56; 0,61 e 0,84, respectivamente, para capim cameroon, gliricidia e solo sem cobertura morta. O uso da cobertura do solo com graminea ou leguminosa minimizou de forma expressiva a demanda hidrica da cultura da beterraba (Beta vulgaris).

Growth analysis and yield of tomato crop under different irrigation depths

The influence of irrigation depth was evaluated on tomato crop hybrid Debora plus for salad in a field experiment in split-block design with five treatments (irrigation depth of 40, 60, 80, 100 and 120% of crop evapotranspiration - ETc) and four replications. During the experiment, ten plant samples were collected to determine phytomass and leaf area to estimate plant growth parameters for different depths of irrigation. Results showed maximal growth between 70 and 80 days after transplanting in all treatments. Increase in irrigation depth above 80% of ETc increased crop growth rate (CGR), leaf area index (LAI) and total production of tomato fruits, although same commercial fruit yield was obtained with the lower depths. Therefore, an increase in depth of irrigation above 80% of ETc promotes higher water and energy consumption, without providing an increase in commercial yield of tomato fruits.

Fertigação em mudas de citros utilizando-se mangueiras e microtubos sob regime de escoamento turbulento

The use of localized irrigation using microtube as emitter under turbulent flow regime can be a technically feasible alternative. The objective of this study was to evaluate the performance of a fertigation system in nursery of citrus plants (greenhouse) projected by universal mathematical model, using the microtubes as emitters, under turbulent flow rate and to compare the development of the fertigated plants by microtubes to the system that use the traditional method with hoses. In the size of the length of the emitters was considered the K coefficient of localized energy dissipation using a microtube with internal diameter of 0,761 mm. The fertigation system presented great performance with clogging degree, Christiansen uniformity and emission uniformity values equal to 0,50; 99,95 and 98,21%, respectively, after 160 days of study. Plants that were grown using fertigation with both microtubes and hoses showed no difference as regards to stem diameter and height. Thus, the use of the microtube under turbulent flow rate presented technical feasible for fertigation system.