if the tree is in a location that stays wet for long periods after rain, it may struggle and have the symptoms you describe when we have a wet year like this. It can also be caused by piling mulch up against the trunk. Brush any mulch back away from the trunk until you find the original soil level. Mulch or dirt piled against the bark of the tree slowly strangles the and will eventually kill it. it seems to be the most common reason shrubs and trees die.