No way to know from this vantage point. Likely fungal but could also be bacterial or viral. If fungal there are fungicides on the market but they do not cure. Fungicides stop progression but do not cure. You could send a sample to Diagnostic Services for identification for a small fee. https://pestid.msu.edu/
If the plant is just partially affected, you could take off the infected leaves, spray with a fungicide, fertilize and water, then watch & wait.
Otherwise, you can read more here: https://www.canr.msu.edu/news/signs_and_symptoms_of_plant_disease_is_it_fungal_viral_or_bacterial