José Eduardo B. A. Monteiro

Estimação da área foliar do algodoeiro por meio de dimensões e massa das folhas

ABSTRACT COTTON LEAF AREA ESTIMATES BASED ON LEAF DIMENSIONS AND DRY MASS METHODS The objective of this study was to evaluate two different methods to estimate cotton leaf area(LA), based on leaf dimensions (length - L and width - W) and leaf dry mass (DM). Two cultivars, IAC 23and Coodetec 401, were used. For leaf dimensions method, leaves were classified by age: young, heart-shape, and mature. For each age class, a leaf shape factor (LSF) was obtained by simple linear regressionbetween L*W and LA. For leaf dry mass method, leaves were classified in new and mature and a leafdry mass factor (LDMF) was obtained by simple linear regression between DM and LA. LA estimates thetwo methods were compared to LA measured in an independent sample. Good accuracy was observedwith both methods, but leaf dry mass method presented a better performance with r 2 ranging from 0.94to 0.98 and regression slopes between 0.97 and 1.00, when regression line was forced thought the origin.In this case there is and advantage since leaf dry mass method is less time-consuming.

Obtaining weather data for input to crop disease-warning systems: leaf wetness duration as a case study

Os sistemas de alerta fitossanitario sao ferramentas de suporte a decisao desenvolvidos para ajudar os agricultures a determinar o melhor momento da aplicacao das medidas de controle para combater as doencas de plantas. As variaveis meteorologicas sao dados de entrada quase que obrigatorios desses sistemas. Este trabalho apresenta uma revisao sobre os meios pelos quais as variaveis meteorologicas sao coletadas para serem usadas como dados de entrada em sistemas de alerta fitossanitario e sobre os desafios associados a logistica de obtencao desses dados. Essa revisao compara o monitoramento meteorologico ao nivel do produtor, nas propriedades agricolas, com aquele feito ao nivel de redes de estacoes meteorologicas, assim como discute as vantagens e desvantagens entre medir e estimar tais variaveis meteorologicas. Especial enfase e dada a duracao do periodo de molhamento foliar (DPM), nao somente pela sua importância como dado de entrada em diversos sistemas de alerta fitossanitario, mas tambem pelo desafio de se obter dados acurados dessa variavel. Pode-se concluir, apos ampla discussao do assunto, que nao ha um metodo unico e melhor para se obter os dados meteorologicos para uso em sistemas de alerta fitossanitario; por outro lado, as circunstâncias a nivel local, regional e nacional provavelmente influenciam a estrategia de maior sucesso.

Adaptation of an Apple Sooty Blotch and Flyspeck Warning System for the Upper Midwest United States

A warning system for sooty blotch and flyspeck (SBFS) of apple, developed in the southeastern United States, uses cumulative hours of leaf wetness duration (LWD) to predict the timing of the first appearance of signs. In the Upper Midwest United States, however, this warning system has resulted in sporadic disease control failures. The purpose of the present study was to determine whether the warning systems algorithm could be modified to provide more reliable assessment of SBFS risk. Hourly LWD, rainfall, relative humidity (RH), and temperature data were collected from orchards in Iowa, North Carolina, and Wisconsin in 2005 and 2006. Timing of the first appearance of SBFS signs was determined by weekly scouting. Preliminary analysis using scatterplots and boxplots suggested that cumulative hours of RH ≥ 97% could be a useful predictor of SBFS appearance. Receiver operating characteristic curve analysis was used to compare the predictive performance of cumulative LWD and cumulative hours of RH ≥ 97%. Cumulative hours of RH ≥ 97% was a more conservative and accurate predictor than cumulative LWD for 15 site years in the Upper Midwest, but not for four site years in North Carolina. Performance of the SBFS warning system in the Upper Midwest and climatically similar regions may be improved if cumulative hours of RH ≥ 97% were substituted for cumulative LWD to predict the first appearance of SBFS.

Spatial Heterogeneity of Leaf Wetness Duration in Apple Trees and Its Influence on Performance of a Warning System for Sooty Blotch and Flyspeck

To determine the effect of sensor placement on the performance of a disease-warning system for sooty blotch and flyspeck (SBFS), we measured leaf wetness duration (LWD) at 12 canopy positions in apple trees, then simulated operation of the disease-warning system using LWD measurements from different parts of the canopy. LWD sensors were placed in four trees within one Iowa orchard during two growing seasons, and in one tree in each of four orchards during a single growing season. The LWD measurements revealed substantial heterogeneity among sensor locations. In all data sets, the upper, eastern portion of the canopy had the longest mean daily LWD, and was the first site to form dew and the last to dry. The lower, western portion of the canopy averaged about 3 h less LWD per day than the top of the canopy, and was the last zone where dew formed and the first to dry off. On about 25% of nights when dew occurred in the top of the canopy, no dew formed in the lower, western canopy. Intracanopy variability of LWD was more pronounced when dew was the sole source of wetness than on days when rainfall occurred. Daily LWD in the upper, eastern portion of the canopy was slightly less than reference measurements made at a 0.7-m height over turfgrass located near the orchard. When LWD measurements from several canopy positions were input to the SBFS warning system, timing of occurrence of a fungicide-spray threshold varied by as much as 30 days among canopy positions. Under Iowa conditions, placement of an LWD sensor at an unobstructed site over turfgrass was a fairly accurate surrogate for the wettest part of the canopy. Therefore, such an extra-canopy LWD sensor might be substituted for a within-canopy sensor to enhance operational reliability of the SBFS warning system.

Development of Ramulosis Disease of Cotton Under Controlled Environment and Field Conditions

Colletotrichum gossypii var. cephalosporioides, the fungus that causes ramulosis disease of cotton, is widespread in Brazil and can cause severe yield loss. Because weather conditions greatly affect disease development, the objective of this work was to develop weather-based models to assess disease favorability. Latent period, incidence, and severity of ramulosis symptoms were evaluated in controlled environment experiments using factorial combinations of temperature (15, 20, 25, 30, and 35 degrees C) and leaf wetness duration (0, 4, 8, 16, 32, and 64 h after inoculation). Severity was modeled as an exponential function of leaf wetness duration and temperature. At the optimum temperature of disease development, 27 degrees C, average latent period was 10 days. Maximum ramulosis severity occurred from 20 to 30 degrees C, with sharp decreases at lower and higher temperatures. Ramulosis severity increased as wetness periods were increased from 4 to 32 h. In field experiments at Piracicaba, São Paulo State, Brazil, cotton plots were inoculated (10(5) conidia ml(-1)) and ramulosis severity was evaluated weekly. The model obtained from the controlled environment study was used to generate a disease favorability index for comparison with disease progress rate in the field. Hourly measurements of solar radiation, temperature, relative humidity, leaf wetness duration, rainfall, and wind speed were also evaluated as possible explanatory variables. Both the disease favorability model and a model based on rainfall explained ramulosis growth rate well, with R(2) of 0.89 and 0.91, respectively. They are proposed as models of ramulosis development rate on cotton in Brazil, and weather-disease relationships revealed by this work can form the basis of a warning system for ramulosis development.

Spatial variability of leaf wetness duration in cotton, coffee and banana crop canopies

Despite the importance of leaf wetness duration for plant disease epidemiology, there has been little attention paid to research on how its variability relates to different cropping situations. The objective of this study was to evaluate the spatial variability of leaf wetness duration (LWD) in three crops, comparing these measurements with turfgrass LWD, obtained in a standard weather station. LWD was measured by electronic sensors in three crops with different canopy structures and leaf area: cotton, coffee and banana. For the cotton crop, cylindrical sensors were deployed at the lower third and on the top of the canopy, facing southwest. For the coffee crop, flat plate sensors were installed in the lower third of the canopy facing northeast and southwest; in the middle third facing northeast and southwest; and inside and on the top of the canopy. For the banana canopy, cylindrical sensors were used to measure LWD in the lower third of the canopy and in the upper third of the plant. Turfgrass LWD was simultaneously measured in a nearby standard weather station. The LWD showed different patterns of variation in the three crop canopies. For coffee plants, the longest LWD was found in the lower portions of the canopy; for the banana crop, the upper third of the canopy showed the longest LWD; whereas for the cotton crop no difference was observed between the top and lower third of the canopy. Turfgrass LWD presented a good relationship with LWD measured on the top or in the upper third of the crops. Thus, the estimate of crop LWD can be perfomed based on turfgrass LWD, this being a useful tool for plant disease management purposes for crops in which the longer LWD occurs at the upper canopy portion.

Vector control of induction motor using a sliding mode controller with chattering reduction

This work deals with vector control applied to the three phase induction motor (IM), using the indirect field oriented control (IFOC) technique. In the proposed topology, sliding mode controller with chattering reduction is applied, aiming high dynamic performance in a wide speed range and robust to load disturbances. Therefore, an approach with soft switching hyperbolic tangent function on the controllers is proposed. In order to analyze the control versatility, the usage of the controller in dq axes stator currents, rotor flux and mechanical speed is proposed. The performance of the motor is verified by means of numeric simulations and experimental tests, where good tracking results are obtained.

Filme plástico perfurado em túneis baixos cultivados com alface

The present work was carried out with the objective to evaluate the micrometeorological conditions inside low tunnels cultivated with lettuce. A technique used to improve the ventilation inside the tunnels is the perforation of the plastic film, though still not very well known. Therefore, tunnels were tested without and with lettuce crop, with 0, 5, 10, 15 and 20% of perforated film area and in soil without tunnel, during spring. The meteorological variables used for the evaluation of the treatments were temperature and relative humidity of air. It was verified that the elevation of the temperature inside the protected atmosphere was inversely related to percentage of perforation contrary to the humidity loss for the external atmosphere. The production obtained under protected conditions was higher and of better quality.