The development of a linuron-free weed management strategy for carrot production is essential as a result of the herbicide reevaluation programs launched by the Pest Management Regulatory Agency in Canada for herbicides registered before 1995 and the discovery of linuron-resistant pigweed species in Ontario. Field trials were conducted in one of Ontario’s main carrot-growing regions on high organic soils in 2016 and 2017. Pigweed species seedlings were effectively controlled with PRE treatments of prometryn, pendimethalin, S-metolachlor, or glufosinate. POST treatments of pyroxasulfone and metribuzin followed by predetermined biologically effective dose (≥90% control of pigweed seedlings) of acifluorfen, oxyfluorfen, fluthiacet-methyl, and fomesafen achieved excellent crop selectivity and commercially acceptable pigweed species seedling control under field conditions. Carfentrazone-ethyl or fomesafen applied PRE severely reduced seedling emergence and yield in the wet growing season of 2017. This study demonstrated clearly that an alternative linuron-free strategy can be developed for carrots. The strategy of exploring the potential to use the biologically effective dose of selected herbicides to achieve crop selectivity and control of pigweed species seedlings was verified.

A new, prepackaged mixture of saflufenacil + dimethenamid-P has been introduced for PRE control of grass and broadleaf weeds in corn. Field experiments with this new herbicide combination were conducted in 2008 and 2009 at four locations in southern Ontario, Canada. The objective of this study was to determine the dose of saflufenacil + dimethenamid-P required for overall weed control and species-specific weed control, as well as the dose required for early season weed control when followed with glyphosate at the six- to eight-leaf corn stage. Based on weed dry weight, the GR95 across locations ranged from 126 to 675 g ha−1. The 95% growth reduction (GR95) for common ragweed, common lambsquarters, pigweed, and wild mustard were 933, 325, 186, and 115 g ha−1, respectively. Highest corn yields were achieved with saflufenacil + dimethenamid-P applied alone at doses ranging from 368 to 1470 g ha−1. When followed by glyphosate, the dose range of saflufenacil + dimethenamid-P required to achieve the greatest corn yields was 46 to 1,470 g ha−1. A minimum dose of 184 g ha−1 of saflufenacil + dimethenamid-P followed by glyphosate was required for the yield to exceed that of the single treatment of glyphosate applied alone.

Few studies have examined the combined effect of herbicide-induced stress and arthropod herbivory to reduce weed fitness. The purpose of this study was to quantify the effect of arthropod herbivory on the herbicide dose–response of a perennial weed. Fluroxypyr dose–response bioassays using volunteer potato were conducted in the presence and absence of Colorado potato beetle (CPB) herbivory. Logistic model parameter estimates for leaf area, shoot biomass, tuber number, and tuber biomass were often lower with herbivory, compared with no herbivory. Greater variance of parameter estimates within herbivory plots was attributed largely to differential feeding because CPB density was not manipulated in the field. Results from short-season field studies (1,000 growing degree days [GDD] after postemergence [POST] herbicide application) indicated that herbivory had the most effect on potato during a period that coincided with high CPB density and optimal temperatures for CPB development. Season-long bioassays (> 3,100 GDD after POST) revealed that addition of herbivory reduced herbicide use 65 to > 85%, compared with the dose needed to achieve the same reduction in tuber production in the absence of herbivory. Integrated weed management systems targeting volunteer potato are more effective when fluroxypyr applications are made before periods of high herbivory. Moreover, this article describes an experimental approach contributing to optimization of combined effects of arthropod herbivory and reduced herbicide doses.

The issue of the variation of the surface ultraviolet (UV) environment on Mars was investigated with particular emphasis being placed on the interpretation of data in a biological context. A UV model has been developed to yield the surface UV irradiance at any time and place over the Martian year. Seasonal and diurnal variations were calculated and dose rates evaluated. Biological interpretation of UV doses is performed through the calculation of DNA damage effects upon phage T7 and Uracil, used as examples for biological dosimeters. A solar UV ‘hotspot’ was revealed towards perihelion in the southern hemisphere, with a significant damaging effect upon these species. Diurnal profiles of UV irradiance are also seen to vary markedly between aphelion and perihelion. The effect of UV dose is also discussed in terms of the chemical environment of the Martian regolith, since UV irradiance can reach high enough levels so as to have a significant effect upon the soil chemistry. We show, by assuming that H2O is the main source of hydrogen in the Martian atmosphere, that the stoichiometrically desirable ratio of 2:1 for atmospheric H and O loss rates to space are not maintained and at present the ratio is about 20:1. A large planetary oxygen surface sink is therefore necessary, in contrast with escape to space. This surface oxygen sink has important implications for the oxidation potential and the toxicology of the Martian soil. UV-induced adsorption of {\rm O}_{2}^{-} super-radicals plays an important role in the oxidative environment of the Martian surface, and the biologically damaging areas found in this study are also shown to be regions of high subsurface oxidation. Furthermore, we briefly cover the astrobiological implications for landing sites that are planned for future Mars missions.