Flower Bud Drop (physiological): Open flowers and buds may drop suddenly when one moisture extreme follows another. For example, drought stress followed by adequate moisture may cause such drop. Other extremes in growing conditions may also contribute. Avoid drought stress.
Leaf Spot (fungi – Cercospora spp., Phyllosticta spp. and others): Circular spots occur on leaves which results in their shedding from the plant. Use appropriate foliar fungicides to prevent damage.
Root Knot Nematodes (Meloidogyne spp.): Knots or galls form on roots causing the plant to be inefficient in absorbing water and nutrients. Leaves are small and the plants fail to make normal growth. Use caution when planting to be sure that planting stock is not infested. If yard soil is contaminated, plant shrub in a large container of sterilized soil. This is probably the most serious problem experienced by althea.
Cotton Root Rot (fungus – Phymatotrichum omnivorum): Althea is very susceptible to attack by the cotton root rot fungus that occurs in the soils of central Texas. If this disease is a problem in the area, it may be necessary to grow the plant in a large container of sterilized potting mix or soil.
Leaf Rust (fungus – Kuehneola malvicola): Infection by the leaf rust fungus causes chlorosis and leaf spotting. Infection is characterized by yellow-orange pustules on the lower leaf surface. Fungicide control is usually not necessary.