O controle de plantas daninhas por meio da aplicação de herbicidas de longa atividade residual é importante estratégia para a supressão destas em diferentes épocas do ano. O objetivo deste trabalho foi avaliar a atividade residual de herbicidas, aplicados em pré-emergência da cana-de-açúcar, sobre o controle de corda-de-viola na época seca, e a seletividade dos herbicidas a cultura da cana-de-açúcar. O experimento foi realizado no delineamento experimental de blocos casualizados, com quatro repetições. Os tratamentos foram (g i.a. ha-1): diuron + hexazinone + sulfometuron (1.025,1 + 289 + 24,65); amicarbazone (1.050); amicarbazone e aplicação sequencial de isoxaflutole (700 e 60); sulfentrazone (800); imazapic (133); tebuthiuron e aplicação sequencial de isoxaflutole (750 e 60), e uma testemunha sem aplicação de herbicidas. Os herbicidas diuron + hexazinone + hexazinone e amicarbazone causaram níveis de controle de Ipomoea hederifolia de 96% e 92,5%, respectivamente. Já para a Ipomoea quamoclit, todos os herbicidas estudados proporcionaram excelentes níveis de controle. Para a Ipomoea nil, os herbicidas diuron + hexazinone + sulfometuron, amicarbazone, amicarbazone e isoxaflutole e o sulfentrazone apresentaram níveis de controle de muito bons a excelente, enquanto que o herbicida tebuthiuron e isoxaflutole apenas bom nível de controle (88,8%) e o imazapic com nível insatisfatório de controle (45%). Portanto, pode-se concluir que os herbicidas diuron + hexazinone + sulfometuron (1025 + 289 + 24,65 g i.a. ha-1), amicarbazone (1050 g i.a. ha-1), sulfentrazone (800 g i.a. ha-1), e as aplicações sequenciais de amicarbazone (700 g i.a. ha-1) e isoxaflutole (60 g i.a. ha-1), podem ser considerados como excelentes alternativas para o controle de diferentes espécies de corda-de-viola (I. hederifolia, I. quamoclit e I. nil), enquanto que o herbicida imazapic (133 g i.a. ha-1) e a aplicação sequencial de tebuthiuron (750 g i.a. ha-1) e isoxaflutole (60 g i.a. ha-1) podem ser considerados como alternativas para o controle apenas de Ipomoea quamoclit quando aplicados em pré-emergência da cultura da cana-de-açúcar na época seca.

Field studies were conducted on organic soils in Belle Glade, FL, in 2016 to 2017 to evaluate sugarcane tolerance and fall panicum control with topramezone applied alone or in combination with triazine herbicides (atrazine, metribuzin, ametryn). Treatments included topramezone (25 and 50 g ai ha−1) applied alone or in combination with atrazine (2,240 g ai ha−1), metribuzin (2,240 g ai ha−1), and ametryn (440 g ha−1) on four plant cane varieties to evaluate tolerance, and on second ratoon fields to determine efficacy on fall panicum control. Topramezone applied alone had no effect on sugarcane chlorophyll fluorescence (i.e., the ratio of variable fluorescence to maximum fluorescence), total chlorophyll, and carotenoid 7 to 28 d after treatment (DAT), suggesting sugarcane tolerance. Significant reduction of these parameters occured 7 to 14 DAT when topramezone (50 g ai ha−1) was applied with ametryn or metribuzin; however, reductions were not detected thereafter, indicating recovery. Sugarcane yield was not affected by topramezone applied alone or in combination with the triazine herbicides. Topramezone (50 g ai ha−1) plus metribuzin resulted in acceptable control of fall panicum (84%) with limited to no regrowth of meristematic tissue at sugarcane canopy closure, equivalent to 56 to 70 DAT. These results indicate that when sequential applications of topramezone, applied alone or in combination with these triazine herbicides, are required for efficacious weed control, topramezone applications alone can be made after 7 d, whereas the combinations can be made after 14 or 21 d, depending on sugarcane sensitivity.

No abstract

The detection and monitoring of soybean rust (SBR) through remote sensing is promising because of the importance of the crop and the aspects of the disease.We evaluated the effects of different levels of SBR severity on soybean [Glycine max (L.) Merr.] leaflets reflectance aiming for the construction of a disease classification model. Leaflet reflectance was evaluated on two cultivars (susceptible and partially resistant) at four disease severity levels: healthy, low, moderate, and high.Leaflets were collected in the field and taken to the laboratory for spectral evaluation through the spectrophotometer UV 2700 coupled with Integrating Sphere Attachment ISR-603, in the range of 270-1000 nm. The feasibility of using a collection of vegetation indices (VIs) and data dimensionality reduction through multiple factor analysis (MFA) was evaluated, and a classification model was constructed. Ten algorithms were assessed based on precision, sensibility, and accuracy parameters, using 80% of the dataset as training data and 20% as testing dataset. The visible range and red edge region contributed more significantly to the disease prediction and classification model. The MFA performed satisfactorily in the dimensionality reduction and unveiled the effect of specific wavelengths on the classification of each class. Most of the VIs studied had high correlation performance across the severity classes. Classification accuracy and precision were >70% for all models. Linear support vector machine with the collection of VIs achieved the best results. This study provides a practical path for developing a detection model to be integrated into SBR management programs.

Asulam controls fall panicum (Panicum dichotomiflorum Michx.), the most troublesome annual grass weed in Florida sugarcane. This study was conducted to evaluate the effect of dew on asulam efficacy on fall panicum control when applied using different spray volumes. Fall panicum 30 cm tall with 0, 50, and 100% dew on leaves equivalent to no dew, moderate dew, and heavy dew, respectively, were treated with asulam at 3,700 g ha–1 using spray volumes of 94, 140, 187, and 281 L ha–1. Fall panicum control was rated 28 days after treatment, and aboveground biomass was harvested immediately. The presence or absence of dew and spray volume did not significantly influence asulam efficacy on fall panicum control and aboveground biomass accumulation. Fall panicum was controlled from 89% to 94% at the different dew levels and spray volumes. Heavy dew did not diminish the performance of asulam. The presence of dew on fall panicum foliage probably hydrated the cuticle and aided water-soluble asulam to remain in solution for a longer period, thereby enhancing uptake. The water-holding capacity of fall panicum foliage with the heavy dew and spray volumes was probably not exceeded, resulting in no runoff and no subsequent reduction of control. These results indicate that dew deposition under Florida conditions has no effect on asulam efficacy on fall panicum 30 cm tall or less when applied at commonly used spray volumes of 140 and 187 L ha–1.