Help to see what's wrong with sweet potato, the spots on the leaves are purple!

For the harm of brown spot disease, 10% difenoconazole, 25% benzalkonium bromide (carbofuran), 20% flusilazole prochloraz and 43% tebuconazole can be selected as therapeutic fungicides, and 70% metformin, 80% mancozeb, 25% azoxystrobin and 50% pyrazole azoxystrobin can be combined.