Answer: If the leaf is truly variegated from within, it may be a viral infection or a natural mutation. Often variegated plants are less vigorous than their all green relatives. If the plant is doing poorly you might want to discard it. On the other hand, there are also some foliar problems that can affect daylilies and one of them causes a yellow streaking pattern lengthwise on the leaves, eventually causing browning and the leaf to die off. This is a fungal infection and is worse in wet seasons. Some varieties are more prone to it than others, and although there is no treatment specifically for it, it does seem that keeping the plants divided regularly so they don't become overcrowded helps. Maintaining good air circulation, avoiding overhead watering, and removing infected foliage as it occurs along with a thorough fall clean up seem to help, too.
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