A cedar apple is not from outer space

StoryImage( ‘/Images/Story//Auto-img-111643717617315.jpg’, ‘Photo by Dr. Robert A. Hedeen’, ‘The exotic-looking stage of the life cycle of the cedar apple fungus occurring on the eastern red cedar tree.’);

Those with sharp eyes at this time of the year are apt to notice a strange-looking bit of protoplasm nestled among the leaves and twigs of the eastern red cedar tree, or as it is sometimes called, juniper. The peculiar mass is about an inch in diameter and is reddish orange in color. The eerie thing about it is that it is covered with fleshy, gelatinous, tentacles. If a science fiction writer wanted a model for an extraterrestrial invader from outer space, he or she would not have to look farther.

What we are dealing with is a fungus belonging to the same group of these primitive organisms as mushrooms. It is a stage in the life cycle of the cedar-apple rust to which scientists have given the “jaw-busting” scientific name of Gymnosporangium juniperus-virginineane. This fungal pathogen attacks crabapple and apple trees as well as the eastern red cedar tree. Both the apple and the cedar trees play an essential part in the fungus’ life cycle. To survive, the fungus must move from the cedar to the apple and back to the cedar. (The evolutionary pathway of many organisms is frequently quite complicated).

On the red cedar, swellings or galls (combinations of plant and fungal tissue) develop throughout the tree on the needles and small twigs. As spring progresses, these galls increase in size and develop the exotic, long, snaky-looking tentacles that are technically called telial horns. As spring rains subside, the horns wither away after releasing countless reproductive spores. A dimple-like depression is left at the base of the horn, giving the gall the rough appearance of a small golf ball. The gall then dies, and with it, the death of the twig to its tip.

The spores released by the telial horns become windborne; sometimes traveling several miles to find apple leaves and fruit to infect. Yellow spots appear on the leaves of the apple tree about 10 days after infection but require somewhat more time to make their appearance on the fruit. Severe infection may cause the leaves to die and dangerously defoliate the tree, making it more susceptible to other disease organisms. Infected fruit may lose most of its commercial value as the apples will often become deformed, having developed unevenly.

Two to four weeks after the spots first appear on the apple tree, a spore-producing structure will develop in the center of each spot. A different type of spore is produced here and becomes airborne. It eventually lands on a red cedar tree to reinfect it from midsummer to early fall.

The growth of the galls continues throughout the summer and fall, and the golf ball-like depressions will give rise to the weird-looking tentacles next spring, and the life cycle is complete.

One of the best ways to prevent or control cedar-apple rust is to break the chain of infection. The owner of the orchard should remove all red cedar trees from the vicinity of apple trees. But, as noted, the windborne spores may travel several miles from the cedar to the apple. Certain fungicides do a good job in controlling this plant disease, but should be first applied at the pink bud stage and repeated at 7- to 10-day intervals throughout the period of flower petal fall.

It has always amazed me the way certain living things have developed complex life cycles. Human parasitic worms, for example, sometimes require three different successive hosts to complete their life cycle. And, the microorganisms causing human disease and transmitted by insects require a specific insect species before they can be transmitted to the human host.

But, such things add to the mystique and attraction of biology and natural history.

From the May 18-24, 2005, issue

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