Answer: Check out which leaves are turning brown. If young leaves near the tips are yellowing while older leaves remain green, your plant is exhibiting iron deficiency. If older leaves are the ones browning and dropping, the problem is probably soggy growing conditions which can destroy roots by cutting off their supply of oxygen. Other causes of browning or yellow, dropping leaves are drought, excess fertilizer, herbicide injury, and physical damage to plant roots.
Hope this information helps you troubleshoot and determine just what is going on with your wisteria. Best wishes with your plant.
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