Removal of the plant is better than attempting to control this disease with fungicides. The fungus over-winters on the plant, spores are present all year, and infection can occur when temperatures are mild and moisture is on the needles. Affected branches thin and fall, giving the shrub an open, bare appearance. Microscopic examination of the spores reveals dark, multicelled spores that are longer than they are wide. Dark fungal fruiting structures break through the surface of infected needles. This differs from twig blights which start at branch tips. The disease progresses upward on the shrub and outward toward the branch tips.
The needles of the inner and lower branches are affected first. In the summer, needles become bronzed, tan, and eventually gray. Gymnosporangium clavipes (cedar-quincerust) Gymnosporangium globosum (cedar-hawthorn rust) Gymnosporangium yamadae (Japanese apple rust) The bark on infected twigs flakes away, growth slows, and twigs die back. Slight twig swellings are not obvious except in the spring when their surface is orange with spores. These spots darken and become dull orange to rust colored. Young leaves and twigs have bright-orange spots that look like paint splatters in the spring. In the nursery, apply a fungicide in the mid July through August.Ĭedar-quince, cedar-hawthorn, and Japanese apple rust Prune and destroy galls before the spore horns develop. Their surface may be dimpled like a golf ball. Smooth, round galls on twigs are up to golf ball size.