Physicochemical interactions and viability of <i>Cordyceps fumosorosea</i> associated with adjuvants

Adding adjuvants to crop protection sprays is common practice; however interactions among formulations must be better understood to prevent reducing efficacy, especially for those containing microorganisms for biological control. This study aimed to assess physicochemical interactions, droplet formation, and viability of the fungus Cordyceps fumosorosea mixed with an adjuvant. The experiments followed a completely randomized design with four replications and six treatments. The treatments included the fungus associated with five adjuvants: polyether/silicone copolymer (1 - PSC), alkyl phosphate ester (2 - PAE), soybean oil methyl ester (3 - SME), orange peel oil (4 - OPO), lecithin/propionic acid mixture (5 - LPA), and a control (only fungus) (6). The LPA adjuvant was physically compatible with the fungus, unlike others that showed phase separation. All adjuvants reduced the contact angle and surface tension compared to the control, with treatments PSC and LPA presenting the lowest values, respectively. All adjuvants reduced droplet size compared to the control. Treatment LPA produced the smallest droplet size, the highest risk of drift, and the most droplet uniformity. The highest viscosity values originated from solutions in treatment LPA, followed by PAE. Formulations with the LPA adjuvant plus the bioinsecticide yielded the lowest pH and the highest electrical conductivity values, followed by OPO. Even with the low pH, the LPA treatment did not affect the viability of the entomopathogenic fungus. It is evident that the adjuvants affected the physicochemical characteristics of the solutions, and treatment LPA yielded the best results for physicochemical compatibility, as it did not reduce the viability of the entomopathogenic fungus.