Stinky Irises Caused By Borers

Q: We have brown spots on our bearded iris leaves and stems. Some of them are dying and have a bad smell. Do you have any idea what could be causing this? 

A: You have two problems: iris leaf spot and iris borers. Removing and destroying dead leaves will help control the disease and the insects. The bad smell is caused by iris borers which have entered the iris through the leaves and traveled to the roots. The borers feed on the iris roots and infect them with bacteria, causing the foul smell you notice. If you look at the base of your irises and find rotting tissue, dig the iris up and discard it.

For leaf spot, spray four to six times with chlorothalonil or myclobutanil starting when leaves appear in the spring. Repeat this every 7-10 days.