Effect of addition of adjuvants on physical and chemical characteristics of Bt bioinsecticide mixture

Abstract

Bacillus thuringiensis (Bt) is the main bacterium used in the formulation of bioinsecticides because it produces toxins and spores that are toxic to several orders of insects. The efficacy of Bt bioinsecticide is influenced by the quality of its application. The association with other crop protection products, such as adjuvants, can affect the physical and chemical parameters of the mixture. This study evaluated the physical and chemical parameters, volume median diameter (VMD), uniformity coefficient of droplets (SPAN), percentage of volume in drift droplets (%V <100 µm), contact angle, surface tension, potential of hydrogen (pH) and electrical conductivity (E.C.) of Bt bioinsecticides in concentrated suspension (SC), and wettable powder (WP) formulations associated with adjuvants. The largest droplet diameter and smallest values of drift droplets were found in the WP formulation with lower drift potential. The addition of mineral oil and surfactant to the mixtures of bioinsecticide reduced contact angle values and surface tension of the droplets, resulting in greater spreading of droplets in leaves. The addition of lecithin and propionic-acid-based adjuvants lowered the pH in both formulations. The adjuvants used in this study affected the physical and chemical characteristics of the mixtures, improving or impairing the quality of Bt bioinsecticide applications.

Compatibility of Bt biopesticides and adjuvants for Spodoptera frugiperda control

“…In the present study, higher vegetative growth and sporulation were observed following treatment with the mixture containing Bt biopesticide and LI. The pH ranged from 3.5 for the WP formulations to 4 for the SC formulations 21 , indicating that a pH below 5 does not affect the vegetative growth of colonies and number of spores.…”

“…Although pH is not considered the key determinant of Bt colony growth and sporulation, spore germination was substantially reduced in acidic media with a pH up to 5.0 21 , 32 , whereas spore germination was completely inhibited due to protein solubilization in alkaline media with a pH above 8 33 . In the present study, higher vegetative growth and sporulation were observed following treatment with the mixture containing Bt biopesticide and LI.…”

“…In general, Bt biopesticides are sprayed alone or in combination with adjuvants 20 , 21 . Adjuvant addition to spray liquids has become increasingly relevant due to the protection of droplets and active ingredients, reduction of drift and evaporation, and extension of the spread of droplets on the leaf surface 22 , 23 .…”

“…Nonetheless, Bt biopesticides and adjuvants must be evaluated for compatibility before use in a tank mix, given the effects of adjuvants on the physicochemical 21 and biological characteristics of the spray liquids, such as inhibition or stimulation of the vegetative growth 24 , 25 , reproduction, mutation, and even inactivation of Bt spores and crystals 26 . However, studies on the effects of adjuvants on Bt biopesticides, particularly the viability and field efficiency of Bt, are lacking 27 .…”

Effect of glyphosate and P on the growth and nutrition of Coffea arabica cultivars and on weed control

“…In contrast, Eucalyptus grandis plants subject to P deficiency absorbed more 14 C-glyphosate 12 . These divergences may be associated with the physical–chemical characteristics of the spray solution, since the electrical conductivity, pH, surface tension and viscosity can interfere in the droplet spectrum and influence the interaction of the herbicide with the target surface 19 , 20 .…”