As all herbicides act on pathways or processes crucial to plants, in an inhibitory or stimulatory way, low rates of any herbicide might be used to modulate plant growth, development, or plant composition. Glyphosate is the most used herbicide in the world, and very low rates of this herbicide can stimulate plant growth, an effect called hormesis. Several studies have shown that glyphosate applications at low rates can increase plant growth, induce shikimic acid accumulation, increase photosynthesis and stomatal opening, increase seed production, and shorten the plant life cycle. Low rates of glyphosate applied to leaves have been reported to cause one or more of these effects in an expanding group of species. Under field conditions, pesticide rates are not uniform, causing some target organisms to receive rates that are low enough to cause hormesis. Until the present, low rates of glyphosate have not been recommended as a growth stimulant for crops, because the hormetic dose can vary considerably, depending on many factors. The objective of the present review is to summarize and analyze existing information about the hormetic effects of glyphosate on plants, thus contributing to understanding how glyphosate hormesis takes place and evaluating the potential use of glyphosate to stimulate plant growth. © 2017 Society of Chemical Industry.

Main conclusionInsertion of the gene encoding phosphinothricin acetyltransferase (PAT) has resulted in cotton plants resistant to the herbicide glufosinate. However, the lower expression and commensurate reduction in PAT activity is a key factor in the low level of injury observed in theWideStrike®cotton and relatively high level of resistance observed in LibertyLink®cotton.LibertyLink® cotton cultivars are engineered for glufosinate resistance by overexpressing the bar gene that encodes phosphinothricin acetyltransferase (PAT), whereas the insect-resistant WideStrike® cultivars were obtained using the similar pat gene as a selectable marker. The latter cultivars carry some level of resistance to glufosinate which enticed certain farmers to select this herbicide for weed control with WideStrike® cotton. The potency of glufosinate on conventional FM 993, insect-resistant FM 975WS, and glufosinate-resistant IMACD 6001LL cotton cultivars was evaluated and contrasted to the relative levels of PAT expression and activity. Conventional cotton was sensitive to glufosinate. The single copy of the pat gene present in the insect-resistant cultivar resulted in very low RNA expression of the gene and undetectable PAT activity in in vitro assays. Nonetheless, the presence of this gene provided a good level of resistance to glufosinate in terms of visual injury and effect on photosynthetic electron transport. The injury is proportional to the amount of ammonia accumulation. The strong promoter associated with bar expression in the glufosinate-resistant cultivar led to high RNA expression levels and PAT activity which protected this cultivar from glufosinate injury. While the insect-resistant cultivar demonstrated a good level of resistance to glufosinate, its safety margin is lower than that of the glufosinate-resistant cultivar. Therefore, farmers should be extremely careful in using glufosinate on cultivars not expressly designed and commercialized as resistant to this herbicide.

Glyphosate applied at low doses increased the dry weight of sugarcane and eucalyptus plants in all experiments. This hormetic effect was related to low dose effects on CO assimilation rate, stomatal conductance and transpiration rate, indicating that low glyphosate doses enhance photosynthesis of plants. © 2017 Society of Chemical Industry.

The sulfentrazone is regularly applied to sugarcane crop harvest residue for PRE control of weedy species, especially in the dry season during the year, but little is known about how rainfall timing or crop residue mass affect the release of sulfentrazone into the soil and its subsequent effectiveness. Two experiments were conducted to examine the effects of sugarcane residue mass (5, 10, 15, and 20 t ha−1) and rainfall timing (1, 30, and 60 d after herbicide application) on sulfentrazone retention. Rainfall volumes were simulated at 2.5, 5, 10, 20, 35, 50, and 100 mm. A 20-mm rainfall volume was simulated at 7 and 14 d after the first simulated event. The water passing through the straw was collected after each rainfall simulation. The concentration of sulfentrazone was measured by liquid chromatography and mass spectrometry. The initial 20 mm of rain released the maximum mass of sulfentrazone from the sugarcane residue. The mass of sugarcane residue affected the amount of sulfentrazone recovered. The amount of sulfentrazone released from the residue was significantly reduced by the persistence on the residue surface for long periods before the occurrence of rain. During periods of low rainfall, recommendations for sulfentrazone rate must take into account losses that occur when applied over the harvest residues to design a weed-management plan that does not compromise efficacy and duration of the residual effects.

Objetivou-se com este trabalho avaliar o efeito de pontas de pulverização, pressão e intensidade do vento na deriva gerada em aplicações simuladas de herbicidas aplicados em pré-emergência. Os modelos de pontas de pulverização e as respectivas pressões testadas foram: SF 11002 (207 e 310 kPa), JA-2 (345 e 655 kPa) e AVI 11002 (207 e 414 kPa). As aplicações foram realizadas em dois períodos, em dias com condições de velocidade de vento distintas, em uma área de 1.200 m², localizada na Fazenda Experimental da FCA/UNESP. Um pulverizador com barra de 12 m, 24 bicos e tanque de 600 L foi utilizado nas aplicações. A calda de aplicação foi composta por água e o corante alimentício FDC-1 foi usado como traçador. A deriva foi amostrada por coletores ativos fixados sobre a barra de pulverização. As velocidades mínimas, médias e máximas de vento registradas no primeiro e segundo períodos das aplicações foram de 7, 14 e 23 km h-1 e 1, 5 e 18 km h-1, respectivamente. Nas duas ocasiões de aplicação, as pontas de pulverização com indução de ar AVI 11002 e de jato cônico vazio JA-2 a 655 kPa resultaram nas menores e maiores quantidades de depósito de líquido detectadas, respectivamente. A maior intensidade do vento incrementou a deriva. A redução na pressão pode ser utilizada para controle de deriva, mas a seleção adequada de uma ponta mostrou ser mais eficiente para esse propósito.