Macrophomina phaseolina, causative agent of the plant disease charcoal rot, impacts over 500 plant species, causing devastating crop failures worldwide. In Kansas, it is the biggest cause of soybean crop loss, and disease epidemics are increasingly frequent. Charcoal rot attacks primarily through fungus-infested soil, and traditional pathogen control means, such as natural resistance, crop rotation, and fungicides, have been ineffective or problematic. This study aims to evaluate the effectiveness of exogenous application of small interfering RNA (siRNA) at suppressing the growth of M. phaseolina through knockdown of genes encoding the cell wall-synthesizing enzymes chitin synthase (CHS) and β -1,3-glucan synthase (GLS). Eight CHS and two GLS genes were identified in the species and were found to be highly expressed during host infection through reverse transcription polymerase chain reaction. siRNAs were designed to target two genes, CHS6 and GLS2, and tested through application to M. phaseolina grown in culture. All siRNAs against both genes successfully suppressed growth of the fungus at multiple timepoints and under varied environmental conditions. Quantitative PCR determined this was correlated with decreases in transcript abundances of the target genes. These results indicate exogenous siRNAs can inhibit growth of M. phaseolina by inhibiting the production of enzymes responsible for cell wall synthesis. This knowledge can be applied through host-delivered RNA interference (HD-RNAi) to manage charcoal rot through development of disease-resistant crop lines. In HD-RNAi, siRNAs are designed and engineered into plant genomes. Upon infection, siRNAs expressed in plant cells can enter invading fungus and prevent expression of genes necessary for successful infection.