Herbicides selectivity to Trichoderma ssp. used in the control of white mold in soybean crop

Abstract

The white mold caused by the pathogen Sclerotinia sclerotiorum (Lib.) De Bary is considered a disease that is difficult to control due to the ability to produce a high amount of sclerotia. Among the alternatives for the integrated management of S. sclerotiorum, the use of biological control agents, mainly antagonists of the genus Trichoderma, is extremely important for the control of this disease. However, the use of chemical pesticides can act in an undesirable way in the development of the antagonist, reducing its action potential or causing its impracticability. Therefore, the object was to analyze the compatibility of the tank mixture between herbicides and commercial biological products based on the fungus Trichoderma spp. registered for the soybean crop. The commercial biological products used were based on T. asperellum and T. harzianum, while the commercial herbicides used were constituted by the active ingredients Haloxifope-p-methyl, Glyphosate N-ammonium salt, Fluasifope-p-butyl, Fomesafen, Chlorimuron ethyl and Imazapyc + Imazapyr. In order to determine the selectivity of herbicides to biocontrol agents, in vitro tests were carried out evaluating the rate of mycelial growth rate, production of conidia and the percentage of inhibition of mycelial growth of the antagonist in the presence of the herbicides. In determining the parameters, the constant exposure methodology and the methodology using different exposure times of the biological products in spray syrup with the herbicides were used, simulating the mixture in the tank that occurs at the producer level. In addition, the control of white mold in the field was evaluated according to the treatments, as well as the productivity of each treatment. The results obtained with the methodology of constant exposure of antagonists to herbicides showed that no herbicide was compatible with biological control agents, drastically reducing their functions, especially the production of conidia. In relation to another methodology, it can be observed that the herbicides were compatible with the fungi up to a maximum time of 8 hours of exposure, except for the Glyphosate-based herbicide of N-ammonium salt, which has shown to have fungicidal properties at after a certain exposure time. In the field experiments carried out in the 2019/2020 and 2020/2021 seasons, we can observe that the best treatments in relation to incidence were constituted by the application of antagonists in association with the herbicide based on Imazapyc + Imazapyr, resulting in the greatest reductions in the incidence of white mold in relation to the witness. In the 2020/2021 season, the treatments that contained this mixture were also the most productive. Therefore, although the mechanisms of inhibition of microorganisms by herbicides are little known, it was found that the herbicides used are compatible with antagonists, however compatibility must be analyzed with caution, since some herbicides begin to be incompatible as the exposure time.