Cedar-apple rust in eastern redcedar trees attracts attention every spring

Orange, octopi-looking blobs in trees, known as cedar-apple rust, commonly appear in eastern redcedars after warm, spring rains.

Telial horns from galls on cedar in spring following moist weather. Photo credit: Linda Haugen, USDA Forest Service, Bugwood.org
Telial horns from galls on cedar in spring following moist weather. Photo credit: Linda Haugen, USDA Forest Service, Bugwood.org

With the first warm rains of spring, something that appears to look very unusual is seen in Michigan in eastern redcedar trees. Some people think the tree is blooming with orange, slimy flowers, but others think these could be multi-armed octopi draped randomly on branches. While both are colorful descriptions, neither are correct. It is the yearly arrival of cedar-apple rust that is associated with eastern redcedar trees (Juniperus virginiana). Michigan State University Extension horticulture educators and Master Gardener hotlines receive a flurry of questions following that fateful first warm rain.

Eastern redcedar is a common wild tree that grows throughout a wide portion of the eastern United States from Canada to Florida. Its name was “baton rouge” to the early French settlers. That means “red stick.” The foliage of the tree has a reddish color in colder months and the heartwood is also a reddish color. Baton Rouge, Louisiana, is said to be named from this tree. It is actually classed as a juniper and not a cedar. There are a few other junipers that could also display the galls.

As long as there have been eastern redcedars, there has been cedar-apple rust. It is a fungal disease that goes between two hosts, as indicated by its name. Eastern redcedar is half of this unholy alliance and apples and crabapples make up the other half. In most cases, cedar-apple rust is more damaging to the apple side of the equation.

Eastern redcedars have small, woody, brown growths of twigs from the fungus that grow slowly each year. These look like little deformed golf balls with many tiny dimples on the surface. The galls could range from three-eighths of an inch to over an inch in diameter. The galls sit for almost the entire year and are very inconspicuous. Following a warm rain in the spring, those little dimples on the galls produce multiple orange telial horns that are gelatinous and cover the gall completely. They look like floppy flower petals or slimy fingers. The orange color of the telial horns can vary from intense to a pale orange. With dry weather, the telial horns dry up and drop off.

Depending on the length of the warm rains, the telial horns could last hours or days. If it was only a short time, the galls will produce more telial horns so it could be possible to see several appearances of the colorful telial horns. During the period that the telial horns are present, basidiospores are produced and float away on the damp air. These are the fruiting bodies needed to reproduce the fungus. If they settle on apple or crabapple leaves, the next half of the story starts. Leaves will develop yellow, orange and red spots and could possibly defoliate later in the season.

Owners of eastern redcedars can try to control cedar-apple rust by picking off the little woody golf balls that are home to the fungus. Then it’s the old “B or B treatment:” burn or bury them. Apple and crabapple owners within several miles of you will be thankful.

In many areas of Michigan, the orange telial spores have only appeared for a day or two because of rain patterns. Smart gardeners don’t get too excited about cedar-apple rust on eastern redcedars, but there may be more colorful activities yet to come. After the next rain, look to the eastern redcedars for possible orange starfish visitors.

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