DISEASES of Hibiscus syriacus

Flower    Leaf    Stem    Root

FLOWER:

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. TAMU

Bud drop can be caused by too much or too little  water or over fertilization.  MSU

Flowers may be infected with blight caused by  Botrytis cinerea.  Use sprays of benomyl.  MSU

LEAF:

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. TAMU

If leaf spots  are  seen,  pick  off  and  destroy  the infected  leaves  or  use  sprays  containing  basic  copper sulfate.  MSU

If bacterial leaf spot causes problems,  pick  off  and destroy infected leaves.  No chemical control is listed.  MSU

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. TAMU

Hollyhock Rust (fungus - Puccinia malvacearum) is an autoecious fungus, requiring only one host to complete its life cycle. Symptoms initially appear as light yellow-orange spots on the upper surface of leaves of the various hosts. Ultimately brown pustules develop beneath these light spots on the underside of leaves. Pustules may also develop on the upper side of the leaves (a different spore stage) and on stems and green flower parts. In severe infestations leaves dry and hang down along the stem. CSU

STEM:

Canker  can  kill branches or entire  plants.   Bright, reddish-orange  fruiting bodies may appear on the bark.   No chemical control is available.  Prune out infected branches. MSU

ROOT:

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. TAMU