The Slimy Scourge: Cedar Apple Rust Disease

Slimy is not a term applied to anything in a positive light. In the pantheon of pejoratives it is only slightly better than being identified as totally disgusting.

When applied to people it serves as a verbal warning that something bad is likely to occur. It is indicative of deceitful and dishonest qualities that are covered by a slick exterior upon which respect and honor will never adhere.

The word is occasionally applied to the repulsive feature of some culinary options. Boiled okra is an example which has the viscous quality that necessitates very little chewing before swallowing.

In the wilds of north Florida, snails and slugs are often identified as slimy. They even leave slime trails which likely terminate with their demise if located in the home landscape or vegetable garden.

Another slimy appearance in the spring is cedar apple rust disease. As the common name implies, this condition affects cedars (and others in the Juniper genus), and apple and crabapple trees (both in the Malus genus).

The rust red slimy eruption on the branches of cedar trees is a certain indicator of cedar apple rust disease which will soon infect apple and crabapple trees.

After overwintering on cedars, the spiky appearing disease galls convert to a slimy, rust colored eruption of the trunks and branches. Easily overlooked, the gooey substance’s muted appearance is hidden by the greenery of the cedars.

Gymnoporangium juniper-virginianae, as this plant pathogen is scientifically known, is actively spreading its spores in the warm and wet early days of spring. Winds distribute the spores to apples and crabapples which are in the early budding phase of development after the winter dormancy.

After arriving on the apple’s leaves or buds, the spores germinate and penetrate the tree’s tissues. Under ideal conditions, the disease can become established on the apple is less than a day.

Yellow lesions appear on the apple tree’s leaves, twigs and fruit in a few weeks. As the growing season progresses, the spots enlarge and darken into orange or red and may contain concentric circles. Late in season black spots appear on the orange or red leaf spots.  

The disease cosmetically blemishes the fruit and overall appearance of the apple or crabapple tree. Leaves displaying symptoms may drop prematurely and affect the tree’s ability to achieve maximum photosynthesis.

In late summer, spores are release from the infected apple tree’s leaves. As earlier in the year, the spores of this rust disease are spread on the winds.

The spores commonly lodge in the bark’s splits, crevices of twigs and where the needles emerge from the branches. After germinating the fungus produces a pea-sized gall which grows to maturity over a two year period.

During the second year the cedar apple rust fungus completes the disease’s cycle by releasing spores from its slimy eruption in spring. Left to chance, infections depend on the wind’s direction.

Apples are not a commercial crop in Florida, but several cultivars have achieved moderate popularity in home orchards. Controlling exposure, for fruiting apple trees and ornamental crabapples, to cedar apple rust disease can prove very challenging.

In areas where apples are a commercial crop cedars and other closely related junipers are removed from within 1.5 miles of the groves. This option is not practical for home owners.

The only realistic option is to use fungicides registered for treatment of this pathology. It will not eliminate the problem, but it can help control the symptoms and spread.

If only there was an effective fungicide for all the other slimy issues in the environment.

About the author
Les Harrison

Les Harrison is a longtime resident of north Florida, having attended public schools in three counties. He has a Bachelor Degree from the University of Florida in Journalism and a Master’s of Science from Auburn University in Agricultural Economics. He is the author of more than 2000 newspaper and magazine stories and journal articles. During his career, he held positions in private, government and educational (university level) sectors. He holds the title of Extension Agent Emeritus. He can be reached at harrison.gl@gmail.com.

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