Lily of the Valley ((Convallaria) is a tough, long lived perennial that suffers from very few disease or instect problems. Because they are one of the earliest plants to bloom in the garden, they also show wear and tear earlier than others.  By the end of the summer they often look pretty ratty.  After many years in one location it is beneficial to these plants to be dug up, thinned out and moved, or replanted in refreshed soil.  They prefer a shady to partly shady location and may show browning if the get "sun-burned".

Here is a list of some of the most common problems that could afflict your plant: