Gardening: Autumn color on summer trees may be an issue with the roots
Some of the trees in the valley have one, or more, branches already showing their autumn color, yet the rest of the tree is its normal color. Maples with deep red as their autumn color and green as their summer color will sometimes have a branch already showing red at this time of year. Globe willows, normally green at this time of year will have portions of their leaves yellow as if autumn has already arrived. These colors are present even when leaves are green, but are masked by the green of the chlorophyll. As the chlorophyll degrades, the yellows and reds appear. If the tree, or shrub, had an outstanding year and the leaves produced an abundance of glucose, more anthocyanin pigment will be produced creating an even denser red.
Normally fall color, due to the degradation of chlorophyll, appears when days get shorter and photosynthesis shuts down. Obviously the appearance of fall color in the summer is not due to a change in day length, but to the slow decline of the chlorophyll due to the leaves on a branch not receiving adequate water and nutrition. The nutrients needed to keep chlorophyll happy are nitrogen and magnesium, which make up the molecular structure, and iron, which helps maintain the function of chlorophyll. When these nutrients are not available in an adequate concentration, the chlorophyll degrades.
While magnesium and iron are seldom deficient in our soils, nitrogen deficiency can be a problem. Why would only one branch out of hundreds show its fall color at this time of year? Something is preventing the movement of the required nutrients and water into the leaves. If the tree involved was a pear tree, the answer might be a phytoplasma, an organism known to slow the movement of glucose to the roots resulting in the slow decline of the roots. This results in a reduction of water and nutrient uptake creating a slow decline of the leaves. Ash trees are also invaded by this organism. Other conditions can also cause the slow decline of branches.
When a tree or branch slowly declines the cause needs to be identified and corrected if possible. Is something going on with the root? Is there damage to the trunk or branch? What is causing the reduction of water and nutrient movement to the branch? To identify the cause you need to use your detective skills or contact someone who can help you identify the problem. As the leaves decline they are often attacked be insects and/or mites. These pests are attracted to the declining stressed leaves as a result of the shift in volatile organic compounds given off by the leaves. If the stress is not identified and corrected it is highly likely the affected branch (or branches) will die. The best thing to do when you notice the abnormal color change is to identify the problem, and correct it if possible before it affects and kills the whole tree.
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