Answer: The problem of yellowing leaves may just indicate a nutrient deficiency, or it could be symptomatic of a serious disease. If the new leaves are smaller than normal, unusually pale or yellow green, or appear stunted, it could indicate root rot (Phytophthora). The disease is associated with excessive soil moisture due to overirrigation or poor drainage. It's possible to prolong the life of an infected tree with careful management of water. Phytophthora is a soil inhabiting fungus that is favored by wet conditions. If the soil is completely dried out, the fungal spores will survive for only a few months. Wet soil, on the other hand, will allow the spores to germinate.
Black spots on the leaves can be signs of disease, as well. Be sure to rake the fallen leaves and remove them from the area, to stop potential reinfection. Holes in leaves are generally a sign of insects - usually they are long gone by the time you notice the holes, so no control is necessary.
Weakened plants often attract insect and secondary disease problems so watch your tree carefully and try to correct any excessive moisture conditions around the base and roots of the tree.
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