|Here, the front leaves were flopping forward.
|Hollow centres towards the base of rhizome.
I began to look further, inside the the centre of the plant to see blades of iris leaves with this streaking and damage. I pulled on these and they came free easily, revealing a hollow centre to each segment.
When you see this tunneling, please remove the entire leafy section, and break off the adjoining rhizome.
|Pink bodied, with a brown shiny head.
|Here I cut the rhizome root in half, and you see the tunnel and pithy excrement of the larvae.
The rot can become quite noticable, making the foliage droop or collapse as I saw today.
Here is the larvae as I removed it from the rhizome hide-away:
Remove and squish all these larvae, to prevent them from becoming adult moths. The larvae move to the rhizomes to feed and to pupate, becoming adult brown moths.
Adult moths will lay eggs in late August to September at the base of the Iris to start the whole process over again.
Control: The best control is a thorough tidy up at this time of year. Remove any streaking foliage, and dying leaf blades. Examine any blades and rhizomes for tunnels.
Divide your Iris every 2nd to 3rd year. This should be done in late August - September. By doing this, you take notice of the rhizomes and also gives the plant room to grow more abundantly.
In spring, when the foliage reaches about 6 inches tall, the eggs of the Iris Borer will have hatched and tiny larvae will begin to bore through the blades. You'll see pin-pricked sized holes with some streaking. Squishing tunnels or removing the damaged leaf blades will reduce their numbers significantly.
Thoroughly keep your iris free of debris in August/September. This will deter the adult moth from laying eggs at the base of the plants. In late fall, clean up all the dead and dying leafy blades from frost damage. This will help expose overwintering eggs that you may have missed. Destroy and don't compost any of the foliage.
Keep an eye on your iris throughout the growing season for signs of damage.
Hope that helps!