Is it in a pot? as pieris like an acid soil so if in a pot you should use ericacous compost and if you haven't this maybe the reason for it showing it's not happy. If it is in the ground, have a look at other plants in the ground and in neighbours, plants like heathers and rhododendrons are all acid lovers so a good indication of what your local soil is like.
Fresh tips of Pieris are very delicate and can brown if the plant has dried out or could be wind damage. Lobelia planted with it will not be the cause.