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The essential oils from four Eucalyptus species (E. spathulata, E. salubris, E. brockwayii and E. dundasii) have been previously confirmed to have stronger inhibitory effects on germination and seedling growth of silverleaf nightshade (Solanum elaeagnifolium Cav.). The aqueous volatile fractions (AVFs) were the water soluble volatile fractions produced together with the essential oils (water insoluble fractions) during the steam distillation process. The aim of this study was to further assess the phytotoxicity of AVFs from the four Eucalyptus species and their chemical composition. The fresh leaves of the four Eucalyptus species were used for the extraction of AVFs. The AVFs were tested for their phytotoxic effects on the perennial weed, silverleaf nightshade under laboratory conditions. The chemical compositions of the AVFs were determined by gas chromatograph–mass spectrometry (GC-MS). Our results showed that the AVFs had strong inhibition on the germination and seedling growth of silverleaf nightshade. The inhibition index increased with the increasing concentrations of AVFs. The inhibitory effects of the AVFs varied between different Eucalyptus species. The AVF from E. salubris demonstrated the highest inhibitory activity on the weed tested, with complete inhibition on germination and seedling growth at a concentration of 75%. The GC-MS analysis revealed that 1,8-cineole, isopentyl isovalerate, isomenthol, pinocarvone, trans-pinocarveol, alpha-terpineol and globulol were the main compounds in the AVFs. These results indicated that all AVFs tested had differential inhibition on the germination and seedling growth of silverleaf nightshade, which could be due to the joint effects of compounds present in the AVFs as these compounds were present in different quantities and ratio between Eucalyptus species. [ABSTRACT FROM AUTHOR]

Silverleaf nightshade (Solanum elaeagnifolium Cav.) is a problematic summer-growing perennial weed in Australia. The genetic diversity of silverleaf nightshade is poorly understood. Nine silverleaf nightshade specific and 10 cross-species simple sequence repeat (SSR) primer pairs were utilised to investigate the genetic variations among 94 silverleaf night-shade populations collected in Australia. High genetic diversity was found within silverleaf nightshade populations, with an average genetic similarity of 0.43. The Unweighted Pair Group Method with Arithmetic mean based dendrogram indicated the presence of genetically diverse silverleaf nightshade populations in Australia. However, no well supported genetic structure was found. The Mantel test indicated that there is no significant correlation between genetic variation and geographic distance. These results suggested a lack of geographic structure in genetic diversity, which is probably due to the long distance spread of seeds of silverleaf nightshade. The high genetic diversity of silverleaf nightshade could contribute to the inconsistency in control efficacy between populations. [ABSTRACT FROM AUTHOR]

The article reports on the survey of 400 growers of maize, soybeans and cotton conducted in the United States to determine perceptions, experiences and management practices with glyphosate-resistant weeds. It discusses that 24% of northern growers and 39% of southern growers thought they had glyphosphate weed resistance on their farm. It infers that glyphosphate weed resistance is one of the primary problem for glyphosphate-resistant (GR) soybean and cotton planters. An overview on the glyphosphate-resistant weeds is presented.