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Disease:
Hawthorn and Quince Rusts

Hawthorn rust:
Gymnosporangium globosum

Quince rust:
Gymnosporangium clavipes

Figure 1. Shoot gall on Washington 
hawthorn resulting from cedar-quince rust.  

Figure 2. Multiple galls of cedar quince rust on Washington hawthorn.

Introduction: Hawthorn and quince rusts spend part of their life cycle on rosaceous hosts such as hawthorn, flowering crabapple and apple, and another portion on junipers.  These rusts can significantly impact hawthorn production in the nursery, especially in locations where large populations of native junipers (the alternate host) are nearby. Hawthorn rust causes leaf spotting and premature defoliation, whereas quince rust causes fruit distortion, twig galls and branch dieback. Damage to juniper hosts is usually minimal but may become injurious on susceptible cultivars (see section on juniper diseases for details).

Symptoms: Initial symptoms of hawthorn rust appear in mid-May to early June. Infection usually is limited to the leaves and rarely occurs on fruit or twigs. Small, pale yellow spots approximately 6 mm in diameter first develop on the upper leaf surface. The spots are slightly raised and eventually turn a shiny, yellow-orange. Pinpoint, black fruiting structures called pycnia form in the center of the spot. In mid-summer, off-white to light orange, 3-mm-long, cylindrical tubes called aecia form on the lower leaf surface. These protruding aecial tubes may be scattered or grouped in circles on the bottom surface of the leaf. Leaves with multiple spots drop prematurely, and heavily infected trees may be defoliated by late summer.

Quince rust primarily attacks the fruit and succulent stem growth. Leaf lesions are not common. Infected fruit are covered with protruding off-white aecia of the fungus. The fruit eventually die, dry out and drop from the tree. Petioles, thorns and twigs begin to swell and turn orange soon after infection.

Spindle-shaped galls 5 to 10 cm long and covered with aecia are eventually formed. By late summer, twig galls expand and girdle the stem, resulting in branch dieback. These dead twigs may remain attached to the tree for several years. Occasionally, living rust galls may persist on twigs for more than one season.

Epidemiology: Hawthorn and quince rusts have complex life cycles similar to cedar-apple rust. Hawthorn infection occurs in spring as spores (basidiospores) produced on the juniper host are blown to the foliage and twigs of hawthorns. Infection of hawthorns may continue into early June as long as the basidiospores are released from active juniper galls and weather is favorable. Aeciospores produced on hawthorn leaves in summer are wind-blown to junipers where they infect and produce perennial, spheroid (hawthorn rust) or spindle-shaped (quince rust) galls.

Host range: There are no reports of commercially available hawthorn species or cultivars with resistance to quince rust. C. crusgalli var. inermis and C. phaenopyrum are particularly susceptible. Other hosts of quince rust include Amelanchier, Aronia, Chaenomeles, Cydonia, Juniperus, Malus, Mespilus, Photinia, and Pyrus.

English hawthorn is reported to be resistant to hawthorn rust, but most other species and cultivars appear to be susceptible. Other hosts of hawthorn rust include Amelanchier, Juniperus, Malus, Pyrus and Sorbus.

Figure 3.  Cedar quince rust on juniper

Management: Where possible, eliminate susceptible junipers within a one-to-three-kilometer radius of hawthorn. Elimination of this alternate host disrupts the life cycle of the rust fungi. Unfortunately, eradication is often difficult to implement in urban areas or other locations where junipers are abundant. Nevertheless, try to locate susceptible hawthorns as far as possible from juniper plantings.

During the winter, prune out all quince galls remaining on branches, twigs, and thorns. Although most of these galls are dead, some may survive for more than one year and can therefore serve as a source of spores for infection of junipers.

Preventive fungicide applications may be required in locations where hawthorn and quince rusts are perennial problems. Fungicide timing is similar to that for cedar-apple rust on flowering crabapple. Make the first application to hawthorns when the orange telial galls on junipers become gelatinous (usually at flower bloom on hawthorn) and make additional applications at regular intervals to protect newly developing foliage. Fungicide applications to hawthorns are not required after the juniper galls become dry and inactive. This is typically late May to early June in Kansas. Our research indicates that two applications of a triazole fungicide such as propiconazole, myclobutanil, or tridiamefon at three-week intervals beginning shortly after bloom is effective in suppressing quince rust.

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Web updated 9/01/06
Web comments to jpierz@ksu.edu