Have you noticed pink protrusions on the fruit of your
hawthorn or dieback of branches. Check your trees closely.
Cedar-quince rust (Gymnosporangium clavipes) kills hawthorn
fruit and twigs.
Cedar-quince rust affects quince (Chaenomeles), serviceberry
(Amelanchier), hawthorn (Crataegus), mountain ash (Sorbus)
as well as many other plants in the rose family and can cause a
great amount of damage
to the fruits, twigs and thorns of susceptible plants. The
rust fungus requires two different tree species to complete its
lifecycle. On the
primary host, juniper or red cedar, the fungus infects leaves
and soft shoots, becomes perennial in the living bark and causes
girdle twigs and small branches. During damp weather in April
and May, orange spore masses emerge from infected, swollen juniper
twigs and may
be splashed or blown to hawthorn, one of the alternate hosts.
On the hawthorn, this fungus causes distortion of fruit, twigs,
and buds. Fruits become
shrunken and often die; twigs become enlarged and woody. Pinkish-orange
tubes, about the size of a pencil lead, protrude from affected
fruits and twigs and shed orange spores that are splashed or blown
back to the
juniper, completing the life cycle of this rust fungus.
Effective control of this fungal disease includes both cultural
and chemical approaches.
Planting resistant varieties when installing new trees will
reduce the need to invest time and money into chemical control. The
Hawthorns have shown some degree of resistance to rust.
*Crataegus crus-galli (Cockspur Thorn)
*C. laevigata (Autumn Glory)
*C. phaenopyrum (Washington Thorn)
*C. viridis (Winter King)
If rust is a chronic problem causing poor tree vigor, registered
fungicides may be used on the hawthorn. These fungicides are
preventive and must be applied several times during early spring to
maintain a protective
coating on developing twigs and fruit. Fungicides such as chlorothalonil,
mancozeb or triadimefon, when used regularly during infection
periods, will help control hawthorn rust. When spring weather is dry
applications are generally not required. Read and follow label
instructions regarding amounts of fungicide, method of application,
and safety precautions.
For more information, please see the following sites:
--Gail Ruhl, Interim P&PDL Director, Senior Diagnostician,
Dept. of Botany and Plant Pathology, Purdue University
First image courtesy of http://ohioline.osu.edu/hyg-fact/3000/3055.html