Irises are my favorite flowers. I love these regal plants with sword-like foliage and extravagantly ruffled blooms in an array of colors from darkest midnight to the earliest blush of dawn.

After our mild winter and rainy spring, I noticed that some of my irises did not perform well. Nothing serious, just less than robust leaves and short-lived blooms. I wasn’t concerned, but after I received two inquiries about iris health, I decided to take a closer look at iris diseases and pests and how to prevent or combat them.

My friend Betty, who lives near Charleston, South Carolina, asked me on Facebook, “Why are my tall bearded iris leaves turning yellow?”

Yellowing leaves often are the first indication of a health problem caused by soil conditions or the growing environment, both of which can contribute to the development of fungal or bacterial diseases.

Then, it was my turn to ask a question, “What is the soil like,” Betty responded that her irises are growing in sandy soil at...