How to fix cedar rust on fruit trees

How to fix cedar rust on fruit trees

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How to fix cedar rust on fruit trees


Posted by: mortimer, 'The Pine State'

The poor choices of parents and grandparents, as well as the overall vagaries of weather, combine to make perfect weather for a destructive disease.

Such is the case for cedar rust, a fungal disease that affects most if not all species of eastern white cedar, including red and white, but also red, Korean, hybrid white, chinkapin, Florida and noble. It can also be found on honeylocust, black locust and sassafras.

On average, a tree can be expected to yield about half of its original commercial value if it survives cedar rust.

Cedar rust symptoms. Photo: WWUI

This horrible affliction -- which can be the most disabling fungus in North America -- is caused by a fungus of the genus Ceratocystis and is carried by a tiny insect, Ceratitis capitata (previously known as Dendrocerus dorsalis).

Fungal spores (conidia) are carried by the male parent on the wind or by direct contact with infected tissues and organs. Trees become infected by ingesting these spores during the growing season.

During wet and dry seasons the spores germinate and the fungus begins to colonize the host. When the spores settle on leaves, they become spore mats that then turn black as they mature. When the spore mats are exposed to wet, humid conditions they release microscopic needle-like extensions (hairs), which are visible on leaf surfaces.

The disease becomes more severe when conidia are deposited on the branch tips, and during warmer weather when the temperature is within the normal range of 25-50 degrees.

When the needles release during warmer weather, they can roll and drop onto adjacent, lower leaves, causing them to become bleached.

Some of the symptoms of cedar rust include:

Growth stunting

Tree trunks in leaf and

Dry foliage

Decorticated branches with rusty cankers

Fallen branches


Entirety of the foliage will often turn yellow and fall early.

Diseased branches are inedible.

Traditional, amateur control measures include cutting down diseased trees. This is never a desirable option for many arborists, because it leaves the trunks and limbs to attract animals, which may then create a difficult situation for future tree care.

Using the latest chemical solutions would be beneficial. While such use is not out of the question for some, we would suggest that it is better to use more environmentally friendly alternatives.

In most cases, with less than ideal cultural practices, chemical control is required. Copper sprays are generally very effective at slowing the spread of cedar rust. They are generally used in combination with flumioxazin (an azole). However, the effectiveness is short lived, since the fungus continues to gain a foothold.

Tree developers would do well to avoid the use of copper sprays, since application of copper compounds creates copper toxicity. Copper compounds are highly poisonous and can be dangerous to animals and humans, especially to those with any form of heart disease, metal sensitivity or when combined with other substances.

If the cedar is diseased, it should be sprayed in early May before the leaves start to emerge. This allows the tree to take up the compounds prior to leaf production and keep the leaves from getting brown when sprayed. This is not to be confused with December-April fungicide use, which usually kills everything during the wet season, then produces dry leaves in the spring.

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