Why are my soursop tree leaves brown? Should I be fertilizing my soursop with a particular fertilizer?
That is a rather serious fungal/bacterial infection. Apply wettable sulfur to the area. This will kill the infection from the soil. The old affected growth will not recover, but you will know that the treatment is working when the new growth come in clean. Here is an article for their care: https://www.gardeningknowhow.com/edible/fruits/soursop/soursop-tree-care.htm