Chicago Botanic Garden

YOUR GARDEN — Plant Information

Pests, Problems, and Diseases

Cedar-Apple, Cedar-Hawthorn & Cedar-Quince Rust

 

Susceptible Plants
Apple and crabapple (Malus), hawthorn (Crataegus), quince (Chaenomeles), red cedar and some junipers (Juniperus)

Description & Symptoms
Hawthorns, Apples, Crabapples, Quince (deciduous, broadleaf host)
Rust is a two-host fungal disease that moves between evergreen cedars or junipers and deciduous hawthorns, apples or quince. Orange, rusty-colored spots appear on the upper surface of leaves in mid- to early July in the Chicago area. Short orange tendrils emerge from the infected spot on the underside of the leaf. Eventually similar symptoms appear on individual fruits, which become encased with threadlike protrusions. Small sections of twigs become covered in a hard, thickened, black fungal growth. In severe cases, the lawn or pavement beneath an infected tree may be covered with bright orange spores.

Cedars and Junipers (needled evergreen)
Yellow or orange gelatinous tendrils emerge in spring from brown galls that form on the branches of cedars and junipers the previous summer.

Timing & Life Cycle
During wet spring weather, spores are released from the orange tendrils that appear to drip from galls on junipers. These spores are blown to hawthorns, apples or quince, where they land on leaves, twigs and fruit. There they become the orange lesions with short, fuzzy protrusions associated with rust diseases. These protrusions release spores that are blown back to the juniper, where in late summer they germinate and form brown galls. This starts the cycle all over again.

Damage
Rust is extremely unsightly on ornamental plants. Fruit is stunted and misshapen. Trees defoliate early.

Treatment & Solutions
Where possible, avoid planting eastern red cedar and other junipers within several hundred feet of apples or hawthorns. However, the two hosts can infect each other from a quarter-mile away. Although the galls do not usually affect the health of red cedars, they are the source of another year of infection and should be pruned out. Early spring preventative fungicide treatment on hawthorns may be warranted in some cases.

 

For more information about chemical treatment of rust, call the Plant Information Hotline at (847) 835-0972.