Here are some of the pathogens and pests that affect plants in the Malvaceae family in California:

Pathogens

• Hollyhock Rust (Puccinia malvacearum). Plants can easily get P. malvacearum from metal fences. Orange-brown pustules on the underside of leaves are indicative of this disease.
• Powdery mildew (dusty white powder covering leaves and stems)
• Botrytis blight has a characteristic gray fungal growth
• Leaf spots caused by pathogens such as Alternaria, Cercospora, Colletotrichum, or Septoria spp., create sharply defined necrotic lesions on mallow leaves.
• Antrhacnose is a disease that causes dark, sunken lesions on the leaves and stems.
• Verticillium is a soil-borne fungus that is difficult to get rid of. Wilting leaves are a symptom.

Pests

• The mallow flea beetle prefers mallows and hollyhocks. This beetle is usually up to 5 mm (0.2 inches) long and can be identified by its yellow-red head and dark blue wing coverlets. Mostly, these pests are not dangerous to the plant.
• The Mallow Leaf Miner (Calycomyza malvae) causes damage to the leaves.
• Bactericera lavaterae (a psyllid that causes galls on Island Mallow)
• Other pest problems include Japanese beetles, spider mites, snails and slugs.

References:

• 13 Common Mallow Plant Diseases to Avoid & Solutions (November 6, 2023 by Davin Eberhardt)
  https://thenatureofhome.com/common-mallow-plant-diseases-solutions/