Hawthorn: Rust

Biology

Rust is a fungal disease typically infecting leaves of hawthorn (occasionally also apple and crabapple). It may also be found on green stems and fruit. Initial symptoms are the presence of yellow to orange spots or pustules on the leaves. Severe infections may cause leaves to turn yellow and drop. Rust on stems and fruit causes these parts to be deformed. Mature sporulating rust infections are characterized by hairlike projections which bear the fungal spores. The alternate hosts for hawthorn rust are junipers, which develop swollen galls along the twigs. The juniper galls release orange spores in the spring.

Management Options

Use Integrated Pest Management (IPM) for successful plant problem management.

Non-chemical Management

Select non-chemical management options as your first choice!

• Plant resistant species or varieties such as Crataegus crus-galli, C. flava, C. intricata, C. laevigata ‘Autumn Glory’, C. phaenopyrum, C. pruinosa, or C. viridis ‘Winter King’.
• Remove alternate hosts (junipers) from the area when practical.
• Prune and destroy diseased leaves and branches on hawthorns in summer before sporulation. Prune out galls on junipers before sporulation in the spring.
• Avoid overhead watering.
• Space plantings and prune to improve air circulation and reduce humidity.

Chemical Management

IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides.

• Protect new growth on hawthorn when fungal infections on juniper are active (between mid-March and mid-May).
• Homeowners should not make foliar applications to trees over 10 ft tall.
• Consult a commercial pesticide applicator for treatment of trees and shrubs over 10 ft. tall.

Approved Pesticides

Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.

• Bonide Fung-onil Multi-Purpose Fungicide Concentrate
  Active ingredient: chlorothalonil [EPA registration number: 60063-9-4]
• Bonide Infuse Systemic Disease Control
  Active ingredient: propiconazole [EPA registration number: 100-773-4]
• GardenTech Daconil Fungicide Concentrate
  Active ingredient: chlorothalonil [EPA registration number: 67572-82-71004]
• Ortho Max Garden Disease Control Concentrate
  Active ingredient: chlorothalonil [EPA registration number: 239-2522]
• Spectracide IMMUNOX Multi-Purpose Fungicide Spray Concentrate
  Active ingredient: myclobutanil [EPA registration number: 9688-123-8845]
• This list may not include all products registered for this use.

Additional Images