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WHAT'S WRONG WITH MY MADRONE?Jim Cooper, WSU Master Gardener, San Juan County posted 09/26/05
Its crooked trunk and thick exfoliating red bark sets the Madrone apart from other native trees in the Pacific Northwest. The Madrone has no real commercial value other than aesthetics. The wood is hard and brittle and it cracks easily. It's not the best for firewood. You can't make a canoe out of its bark. And, the berries taste awful. They are also difficult to start from seed and are prone to transplant failure. However, all of this is of little or no consequence to most of us who consider them to be a highly valued member of our indigenous landscape. Islanders concerned about the abnormal conditions of their Madrone trees routinely contact us with their questions. In recent years, the Pacific Madrone has slipped into serious decline. There are no simple answers for the ongoing decline and death of this species. However, due to the gravity of this problem, more and more research has been focused on the pathology and stress factors involved in this decline. One such study suggests that over 83 fungi and 15 chewing insects are involved in the ongoing problems with these trees ("Lowe 1977 and Ginns 1986"). Stress caused by environmental factors and human interference can weaken the trees and make them more receptive and susceptible to invasion by living factors. These factors and conditions that influence the health of the Madrone are nothing new in plant pathology. However, the relationship between living and non-living factors would appear to be more finely balance with the Madrone than with almost all other plants that we deal with here on the Islands. Adverse environmental and non-living factors are recognized to be a significant detriment to the health and natural resistance of the Madrone. Other than leaf spots and insect activity, the most commonly encountered problem by homeowners is usually associated with human activity such as construction, site disturbance and chemical application (over fertilization, herbicide application, etc.). The Madrone can be very sensitive to slight changes in its surrounding habitat. Trees stressed by human activity frequently go into decline characterized by dieback and smooth black cankers. Natural dieback and cankering also occurs with frequency and can complicate the diagnosis of an unhealthy tree. The Madrone is also very shade intolerant. This intolerance can result in natural dieback of the lower leaves and branches due to poor photosynthesis. This, in turn, can result in a tall spindly tree. If the surrounding shade trees are then removed and exposing the Madrone to more sunlight, the red bark will be shed leaving only the thin bark which is more susceptible to sunscald and can weaken the tree as well as providing an avenue for pathogens to invade the trees tissue. Naturally occurring environmental conditions can also stress the tree and predispose it to disease. Soil composition and compaction, poor drainage, drought and weather factors can, in combination or individually, result in weakening the tree and can reduce it's ability to resist and withstand the introduction of pathogens. Arctic outflows can come down the coast in force and blast the trees with frigid and strong winds. Leaves of the tree can be desiccated along the leaf margins or blacken all the leaves on the tree. These leaves will shed throughout summer and winter giving rise to new growth in the spring and summer. An over abundance of flowers is not only a sign of stress but can also "become" a stress factor in itself. All this can add to the trees problems and aid in their overall decline. Chewing insects can attack the foliage of the Madrone mainly causing cosmetic damage. Insects are not considered a factor in the Madrones' decline. However, heavy infestation of chewing insects can reduce the photosynthetic surface of the leaves causing a reduction in the metabolic function of the tree, thus causing additional stress. However, this stress is considered of little or no importance. Of the fifteen or so insect species that are found on the Madrone, only two of them are of any real concern to us - the leafminer and the shield bearer. The Madrone leafminer (Marmara arbutiella) is the larva of a moth that tunnels through the cambium of the leaf leaving visible white/silver serpentine mines. These "mines" are cosmetic and produce no significant harm. The shield bearer (Coptodisca arbutiella) is a tiny moth that develops as a leafminer producing small blotch-like mines. When feeding is completed, they cut a round section of the leaf and fashion a small shielded case around themselves in which they pupate (the transitional stage between larva and adult). The leaves may have numerous small shot holes in them (similar to those produced by a hole punch) that are caused when the "pupal" cell drops to the ground. Although more damaging than the leafminers, chemical control is not recommended. Foliage diseases of Madrone come in many forms and species. The fungi that cause leaf spots are not a serious threat to the tree unless repeated defoliation occurs. Madrone leaves are primary targets due to their high concentration of sugars. Most of our foliar fungi are more successful at attacking old leaves rather than new ones. The new foliage on the Madrone is rarely infected until fall. These fungal diseases intensify during periods of warm, wet weather. In some years, most of the foliage can be lost due to heavy fungal infections, but usually new leaves will replace this lost foliage in the summer. The good news is that foliar disease of the Madrone is not considered to be a major factor in their decline. Also, defoliation can, and often is, caused by environmental conditions such as drought stress. We are seeing quite a bit of this on the west side of San Juan Island right now. The leaves of otherwise healthy trees are turning brown and dying and will eventually be shed. Now for the bad news - root rots and cankers… Phytophthora cactorum, a fungus, is responsible for a lethal disease of the Madrone that results in root rots and collar rots. This pathogen infects the roots and tree trunk causing a smooth sunken canker at the tree's base. The cankers are brown to black and sometimes appear water-soaked. The infected bark is discolored brown in contrast with the healthy cream-colored inner bark. These cankers will eventually girdle and kill the tree. Trees in poorly drained soil are the most susceptible to this fungus. Unfortunately, there are no fungicides registered for this disease. Cultural control may be of some value. Avoid wounding the trees. Small cankers may be removed surgically with some success if all discolored wood and bark is removed and destroyed. Other than these measures and allowing for good drainage, there is not much we can do. Fortunately, Phytophthora root and collar rot is not often seen on the Islands. Fusicoccum (formerly Nattrassia) cankers are widespread and are particularly common on seaside Madrones. This fungus first appears as areas of bark discoloration. The bark will peel off leaving longitudinally cracked wood that develops into the canker. A callus ridge will form around its margin. These cankers can be observed on twigs, branches and trunks of all ages of Madrones, and they can appear blackened as though they had been in a fire. These cankers most commonly occur on tree parts exposed to strong sun or injured by pruning or other mechanical causes. In the more advanced stages, these cankers can become large, gnarly and, all in all, quite impressive. It is not known exactly what the long-term effects of this pathogen will be, but I'm sure it will be a major contributor in the overall decline of the Madrone. The prognosis for the survival of this species is, at this time, not very encouraging. The decline of the Madrone is real, measurable and progressing. However, don't give up hope. Species change and adapt to different stimuli and conditions. Perhaps, given time, the Madrone will adjust to future environmental and biological conditions and continue to survive. Research is continuing in this field, and we are learning more about the pathology and culture of the Pacific Madrone all the time. In contrast to this ongoing decline there are young vigorous madrone trees growing up along highways, in parking lot medians and in other urban situations. It now appears that madrones can thrive in a wider variety of conditions than found in their natural habitat if they are established as juveniles in these new locations. Madrones may, with help, find new niches in many parts of the urban landscape and, hopefully, be successful. Propagation by seed is difficult but progress is being made every day. In the meantime, be gentle with your trees. Clean up dead leaves and branches. Prune out dead, dying and diseased wood with caution. Encourage good air circulation. Watering, fertilizing and chemical spraying are not recommended for our native Madrone. Prevent root damage and wounding of your trees, and keep the disruption of the surrounding area to a minimum. An otherwise healthy tree, even though showing overt signs of disease and decline, may survive for years and continue to be an important member of our plant community. For more information or questions, please contact the Washington State University Extension or one of our local Master Gardeners. |
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