| Cedar-apple rust (Gymnosporangium juniperivirginianae),
cedar-hawthorn rust (G. globosum),
and cedar-quince rust (G. clavipes) are closely
related rust diseases that require two hosts to
complete their life cycle. All three rusts can infect
most varieties of eastern red cedar (Juniperus
virginiana) as well as many other junipers and an
alternate host. Cedar-quince rust has the broadest
host range and can affect many genera in the rose
family including apple, crabapple, pears, quince,
hawthorn, serviceberry, mountain-ash, flowering
quince, cotoneaster, chokecherry, and photinia.
Symptoms and Diagnosis
Symptoms on juniper: Perennial, elongated
swellings on the tips of twigs and branches, which
may crack and form cankers, are symptoms of cedar quince
rust on red cedars and junipers. In damp
spring weather, cushion-shaped, orange, gelatinous
blisters burst through the bark where the branches
are swollen. Cedar-quince rust disease damages the
ornamental value of susceptible cedars and junipers,
killing young branches and weakening plants when
cankers occur on the main trunk.
Symptoms on apple and other hosts: Young
branches and fruit (not leaves) are usually infected
and symptoms vary widely among the various hosts.
On hawthorn, the pinkish aecia (tubes) occur mainly
on branches, thorns, and fruit. Hawthorn and
serviceberry fruit often becomes heavily covered
with aecia. Branch and thorn infections result in
spindle-shaped, perennial cankers that expand each
growing season. However, most infected branches
are girdled by the canker during the second season,
causing dieback to a bud or side-shoot.
Life Cycle
Basidiospores that are released from the juniper gall
telial swellings infect stems and fruit of quince and
the other deciduous hosts. Seven to ten days after
infection, spots or swellings develop, followed a few
days later by the formation of tiny black dots within
the spots. Four to seven weeks later, aecia are
formed. Aeciospores, released from the aecia during
rain or as morning humidity lowers, become
airborne and infect susceptible junipers during late
summer and fall.
The following spring (or one year later), swellings
(consisting of both fungal and host plant tissues)
develop on the juniper host. When the swellings are
mature, a few hours of wet, cool (74 to 78 degrees
F) spring weather are sufficient for repeated telial
swelling and the release of basidiospores that infect
quince and other deciduous hosts. The cedar-quince
rust galls may remain infectious for 4–6 years or
more (up to 20), whereas the cedar-apple gall is
only infectious for one year.
Integrated Pest Management Strategies
1. Prune. Prune out cankers associated with cedarquince
rusts from landscape junipers and
deciduous host plants. The spread of cedar-quince
rust can be limited by reducing the infested plant
parts. This is practical if a few plants are infected
and the number of galls per plant is limited.
2. Co-exist. Live with the disease. It may disfigure
plants when twigs are infected.
3. preventive fungicide. Use preventive
fungicides labeled for use on quince and other
hosts. Fungicide sprays are aimed at protecting
developing twigs and branches from infection
during the time the galls on the junipers are
orange and gelatinous. This usually lasts for
several weeks and fungicide applications are not
necessary once the galls become dry and
inactive. Always read and follow label directions.
Pesticides registered for use include captan,
chlorothalonil (Daconil), mancozeb, sulphur,
thiram, and ziram.
4. Avoid planting susceptible plants together. Do
not plant junipers close to susceptible varieties of
apples, crabapples, or quince.
5. Resistant varieties. Remove and replace diseased
plants with resistant varieties.
Apples: ‘Redfree’, ‘Liberty’, and
‘William’s Pride’. |
