Growth Regulation and Other Secondary Effects of Herbicides

Abstract

As all herbicides act on pathways or processes crucial to plants, in an inhibitory or stimulatory way, low doses of any herbicide might be used to beneficially modulate plant growth, development, or composition. Glyphosate, the most used herbicide in the world, is widely applied at low rates to ripen sugarcane. Low rates of glyphosate also can stimulate plant growth (this effect is called hormesis). When applied at recommended rates for weed control, glyphosate can inhibit rust diseases in glyphosate-resistant wheat and soybean. Fluridone blocks carotenoid biosynthesis by inhibition of phytoene desaturase and is effective in reducing the production of abscisic acid in drought-stressed plants. Among the acetolactate synthase inhibitors, sulfometuron-methyl is widely used to ripen sugarcane and imidazolinones can be used to suppress turf species growth. The application of protoporphyrinogen oxidase inhibitors can trigger plant defenses against pathogens. Glufosinate, a glutamine synthetase inhibitor, is also known to improve the control of plant diseases. Auxin agonists (i.e., dicamba and 2,4-D) are effective, low-cost plant growth regulators. Currently, auxin agonists are still used in tissue cultures to induce somatic embryogenesis and to control fruit ripening, to reduce drop of fruits, to enlarge fruit size, or to extend the harvest period in citrus orchards. At low doses, triazine herbicides stimulate growth through beneficial effects on nitrogen metabolism and through auxin-like effects. Thus, sublethal doses of several herbicides have applications other than weed control.

Low Doses of Fenoxaprop-P-Ethyl Cause Hormesis in Littleseed Canarygrass and Wild Oat

“…Unintentionally, the herbicide hormesis under field conditions may appear due to herbicide drift, improper application method, improper time of application, dilution by dew drops and rain, weeds coverage by crop plants and/or mulches, herbicide dilution in soil by soil degradation and immobilization and herbicide resistance (Velini et al, 2010;Belz et al, 2011). This phenomenon occasionally becomes beneficial if crop plants are affected by hormetic effects (Velini et al, 2010).…”

“…This phenomenon occasionally becomes beneficial if crop plants are affected by hormetic effects (Velini et al, 2010). However, it may become unwanted and disturb the weed management if hormetic responses are produced in weeds.…”

“…Research addressing these issues is currently absent and the effects of herbicide hormesis on weed growth and weed crop competition are absent. Most of the published research is about the hormetic responses of crops against herbicides (Davies et al, 2003;Duke et al, 2006;Cedergreen et al, 2007;Velini et al, 2010;Belz et al, 2011). However, for practical implementation of herbicide hormesis to improve crop growth and yield, the effects of these lower doses on weed growth should also be considered.…”

Efeitos da associação de glyphosate e fosfito em plantas de milho

“…According to Velini et al (2010) Plants subjected to the application of glyphosate higher dose (720 g ha -1 ) associated with phosphite showed inferior losses of stalk and leaves dry mass, although not statistically significant, than to those who were submitted to the same herbicide dose not associated with phosphite. This behavior confirms the minor intoxication observed in plants subjected to this dose associated with phosphite and, in this way, it promoted a protection of these plants against herbicide phytotoxicity effect.…”

“…Partial blockage of EPSPs, through the application of glyphosate reduced doses, implicated in growth stimulation of various plant species including eucalyptus, pines, maize and soybean (no transgenic and susceptible to glyphosate). The stimulation of plant growth by low doses of a toxic compound is called "hormesis" (Velini et al, 2010). ** Significant by F test at 1% probability level; * significant by F test at 5% probability level.…”