There are only a few problems you should look out for with your Lobelia perennials. Some insects to watch for are aphids, slugs, spider mites, flower thrips, leafhoppers, etc. You may see them feeding on your plant's flowers. Of these pests, aphids are the ones to look out for the most because they appear most frequently. However, these insects hardly cause significant damage to your plants. Your plant could experience some diseases such as root rot, crown rot, leaf spot, rust, etc. The best way to avoid these is to water your plants accordingly, space them properly when planting for air circulation, and overall care for them correctly. If you take good care of your plants, you shouldn't have to worry about many disease infestations.