Selectivity of Pre and Postemergence Herbicides in Single or Combined Applications in Castor Crop

Abstract

One of the main challenges in castor crop (Ricinus communis L.) production is efficient weed management mainly due to limited options of selective herbicides. This study evaluated the selectivity of herbicides applied alone or in combination in pre- and postemergence applications in castor crop. Two field experiments were carried out under irrigation conditions in a semi-arid region of Northeast Brazil. It was found that the visual symptoms of phytointoxication of the herbicides used on castor were mild in both experiments. Consequently, there were no significant interferences on plant height, number of racemes, and grain (seed) yield. Pre-emergence applications (g ha−1) of trifluralin (1800), pendimethalin (1500), clomazone (750), clomazone + trifluralin (750 + 1800), and clomazone + pendimethalin (750 + 1500) followed by chlorimuron-ethyl in postemergence (15 g ha−1) are selective to castor. The application (g ha−1) of pendimethalin + clomazone (1000 + 500) in pre-emergence, associated with chlorimuron-ethyl (10 and 15), metamitron (2800 and 4200), ethoxysulfuron (60 and 80), or halosulfuron-methyl (75 and 112.5) in one or two applications in postemergence, as single or split applications, in an interval of 14 days, are selective to castor crop.

Understanding Mechanisms of Herbicide Selectivity in Agro-Ecosystems: A Review

“…Some authors refer to physiological mechanisms as a biological factor that involves processes that affect the activity and/or the breakdown of the herbicide [17]. These include: differential rate of herbicide absorption, differential rate of herbicide translocation, differential rate of applied herbicide deactivation, and specific herbicide protoplasmic resistance.…”

“…The distribution of herbicide molecules within the plant is also an important factor in selectivity. In cotton plants, lysigenous glands and trichrome hold high concentrations of triazines and substituted ureas lowering the concentration at the site of action [17,19]. Herbicides that get deposited on plant surfaces must first penetrate the non-living barriers on the outer part of a plant which are the cuticle and stomata.…”

“…The pores on the cuticle can fill up in a water-saturated atmosphere to provide an accessible water diffusion continuum. When a plant is under stress, pores fill with air which acts as a barrier but the lipid route will be still available [17]. Moreover, cuticle thickness varies from plant to plant even on the same plant.…”

“…As the leaves mature cuticle composition and thickness differ, thus having an impact on herbicide selectivity. Roots also have a cuticle though it is less thick than the ones on leaves and does not have a waxy layer, making it more permeable than foliar cuticle [17]. Thus, differential penetration is influenced by waxy surfaces, hairy leaf surfaces, and cuticle characteristics.…”

“…Herbicides absorbed through the roots have an additional barrier, the endodermis [17]. The endodermal cell walls are impregnated with suberin that creates the Casparian strip which is impermeable to herbicide penetration.…”