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Juniper Diseases: Rusts, Blights, and Management Strategies

Disease Reference Table

Disease	Symptoms	Pathogen/Cause	Management
Cedar-Apple Rust	Smooth, round galls on twigs up to golf ball size; surface dimpled like golf ball.	Gymnosporangium juniperi-virginianae	Prune and destroy galls before spore horns develop. In nursery, apply fungicide mid-July through August.
Cedar-Quince, Cedar-Hawthorn, Japanese Apple Rust	Young leaves/twigs: bright-orange spots (paint-splatter appearance) in spring; darken to dull orange/rust. Slight twig swellings not obvious except in spring when surface orange with spores. Bark on infected twigs flakes; growth slows; twigs die back.	Gymnosporangium clavipes (cedar-quince rust) Gymnosporangium globosum (cedar-hawthorn rust) Gymnosporangium yamadae (Japanese apple rust)	Prune and destroy galls before spore horns develop. In nursery, apply fungicide mid-July through August.
Cercospora Blight	Summer: needles bronze, tan, then gray. Inner/lower branches affected first; progresses upward and outward toward tips (differs from twig blights starting at tips). Dark fruiting structures break through needle surface. Spores dark, multicelled, longer than wide. Affected branches thin and fall, giving open, bare appearance.	Cercospora sequoiae var. juniperi	Fungus overwinters on plant; spores present year-round; infection when temps mild and moisture on needles. Removal better than fungicide control, but fungicide can be used.
Twig Blight	Tips of branches die, turn brown/ash gray; remain for months. Larger branches invaded and girdled. At dead/live wood junction: small black pimple-like fruiting structures. Spores oval, colorless.	Kabatina or Phomopsis	Prune and destroy infected twigs/branches. Both fungi can occur on same plant. Apply fungicide whenever new growth present.

Cedar-apple rust galls: dormancy in winter, early telial horn emergence, full emergence in spring; Cedar-quince/hawthorn rust gall: young stage and older with telial horns; Twig blight by Phomopsis or Kabatina—microscopic exam of fruiting structures/spores required. Phomopsis produces two spore types in pycnidium; Kabatina forms one type in acervulus.

Plant Disease: Orange Gelatinous Growth on Juniper: Cedar-Apple Rust Explained; Key Diseases of Spartan Juniper Trees and Their Management; Plant Diseases 101: What to Do When Your Plant Looks Sick; Plant Virus Diseases: Symptoms, Transmission, and Control Strategies; Palm Disease Guide: Nutritional, Environmental, and Fungal Disorders; Pansy Disease Management: Anthracnose, Leaf Spots, and Root Rot Control; Cotoneaster Disease Management: Botryosphaeria Canker and Fire Blight Control; Elm Tree Diseases: Symptoms, Causes, and Management Strategies; Common Diseases of Poplar Trees: Identification and Management; Rust Disease: Identification, Control & Prevention

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