Impact of nitrogen fertilization on Mexican rice borer (Lepidoptera: Crambidae) injury and yield in bioenergy sorghum

The Mexican rice borer, Eoreuma loftini (Dyar) (Lepidoptera: Crambidae), is a serious pest of sugarcane (Saccharum spp.), sorghum (Sorghum bicolor (L.) Moench), corn (Zea mays L.), rice (Oryza sativa L.), and related graminaceous bioenergy crops. A two-year field study was conducted in Jefferson County, TX to examine the impact of nitrogen (N) fertilization on E. loftini infestations and subsequent yields in cultivars of high-biomass and sweet sorghum. In 2013, percentage of bored internodes and number of adult emergence holes per stalk increased with higher N rates; however, only the percentage of bored internodes was impacted by N in 2014. Yields from both years indicated that N rate was positively associated with increases in stalk weight and ethanol productivity, but not sucrose concentration. Because higher N rates were associated with increased yields despite having greater levels of E. loftini injury, our data suggest that increases in yield from additional N outweigh decreases from additional E. loftini injury. Fertilization rates maintained between the recommended 45 and 90 kg N/ha minimize risks of negative area-wide impacts from increased production of E. loftini adults, while still allowing for optimum yields.     

Comparison of empirical models for predicting yield loss of irrigated rice (Oryza sativa) mixed with Echinochloa spp.

Crop yield losses due to weeds can be described by empirical models. The objective of this study was to compare empirical models to predict interference by a mixed population of Echinochloa colona and E. crusgalli. in irrigated rice. Three experiments, one under field conditions and two under greenhouse conditions, were set up during the growing season of 2005/2006. The treatments tested in the field were 6 rice cultivars: BRS Atalanta, IRGA 421, IRGA 416, IRGA 417, Avaxi; and BRS Fronteira and 10 Echinochloa spp. densities, naturally present in the soil seedbank under field conditions. The variables soil cover, shoot dry weight of the Echinochloa spp. and their relative mass were evaluated in relation to the rice cultivars. The greenhouse experiments were carried out both in monoculture and replacement series to evaluate shoot dry mass and leaf area production, both for the crop and the weed species. The data obtained for the variables were analysed using linear and non-linear regression models. The fitting of the data to the empirical models varied as a function of the rice cultivars and variables tested. Among the models describing crop yield loss as a function of the evaluated variables, the single-parameter empirical model presented a better prediction than the two-parameter model. For the two-parameter models, yield loss estimation was obtained by the evaluated variable. In general, shoot dry mass of the weed was a better predictor of irrigated rice yield loss than soil cover.     

Evaluation of chlorothalonil and paraffinic oil alone and in combinations with registered fungicides for the control of yellow Sigatoka (Mycosphaerella musicola) of bananas in Northern Queensland,Australia

The efficacy of chlorothalonil and paraffinic oil alone and in combinations with the registered fungicides propiconazole, tebuconazole, difenoconazole, epoxiconazole and pyrimethanil was evaluated in a field experiment over two cropping cycles in 2013 and 2014 in Northern Queensland, Australia, for control of yellow Sigatoka (caused by Mycosphaerella musicola) of banana. The predominantly applied by the banana industry treatment mancozeb with paraffinic oil was included for comparison. The results from the two cropping cycles suggested that all chemicals used with paraffinic oil were as effective or more effective than when applied with chlorothalonil, and chlorothalonil alone. Difenoconazole and epoxiconazole with paraffinic oil followed by propiconazole with paraffinic oil were the most effective treatments. Pyrimethanil and tebuconazole plus chlorothalonil were the least effective treatments. None of the chemical treatments was phytotoxic or reduced yield.