Answer: You didn't identify the plant, so I'm at a loss to provide specific information, but here is some general information:
Pests and diseases may damage leaves, but environmental causes are far more common.
Most trees and shrubs will have a few leaves that suffer damage or disfigurement during the growing season. Following severe winter weather or prolonged summer drought, however, there may be more extensive leaf damage on these plants.
Foliage can be damaged in a number of ways but identifying the causes from leaf symptoms is not always easy. Take into consideration:
When and where a plant is growing - new plants take time to establish.
Soil and root conditions - always examine the condition of the roots to check that they are healthy and have grown out into the soil (established)
Site conditions over the past 12 months - especially if the ground has been waterlogged or very dry.
In some cases, such as when leaves are uniformly yellow, there may be a range of factors to consider and all available information should be assessed. Possible explanations may vary from too much or too little water, too sunny a position or simply the shredding of older lower leaves. Bear in mind that even evergreens discard older leaves, which usually function for three to five years then deteriorate and drop.
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