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Caring for Bearded Iris: Pests and Diseases

10 Jul 2021 1:00 AM | Brenda Peshak

White Bearded Iris

Caring for Bearded Iris is a must.

Bearded Iris are not maintenance free and should be cared for and maintained. Learn about planting and dividing irises HERE.

What to do after blooming…

  • A week or so after blooming is finished, cut off the bloom stalk as close to the rhizome as possible. If you leave it on, the stalk forms seeds that rob the plant of nutrients needed for next year.

Do not cut the leaves back after blooming. The plant needs them for photosynthesis for next year’s growth. (You’ll cut the leaves back later on. See below.

Iris pests, diseases and what to do:


Iris are prone to rot in damp situations or when animals dig around them or step on the rhizome. (Deer and dogs are notorious for this.) How will you know if the rhizome is rotting?

  1. First, it’s “squishy” like a bad carrot or potato—you can feel it with your finger.
  2. Second, you’ll definitely smell it. However, you can still save it if enough is left!

Using a spoon, dig out the “mush” until you reach a solid area, dust with sulfur, and leave it a few days to dry in the sun. (Or, you can leave the clump in place and try your surgery without digging the entire clump. It often works!) If the plant is falling over, however, it’s probably a lost cause so discard it—but not in the compost.

Leaf Spot:

In wet years, leaves may develop leaf spot. If you see these rusty-looking patches, remove the individual leaf (by pulling sideways, not up!) and put it in the trash—not the compost. If you wish, spray leaves with an antifungal.

Iris Borer:

Definitely the most destructive pest is iris borer, and it’s all too prevalent in this area.

What is it? The larva of a moth that lays its eggs on previous year’s weeds or unpruned iris blades. In spring, the eggs hatch into tiny worms that crawl up the blade and chew their way down the blade and then into the rhizome—where they proceed to feed. By late July-early August, they are fat, pink, two-inch (or thereabouts) worms that continue eating into the heart of the rhizome until they move into the soil. If left unchecked, the life cycle will begin anew when the larva pupates into the moth that will then lay eggs for the next year.

What are tell-tale signs of iris borer?

  • Edges of the leaves will look ragged, chewed on.
  • Leaves might be turning yellow.
  • Leaves look water-streaked, or soaked, that’s a sure sign.
  • If you dig up the rhizome and cut it open, you’ll find the culprit. Dig it out and dispose of it. If there’s enough of the rhizome left, you can cut out the rot, dust with sulfur and replant.

How to prevent iris borer?

First, vigilance. Watch the leaves in spring and early summer. If you see chewing and water streaking, you can kill the small borer by pinching the leaves between thumb and forefinger, especially toward the rhizome. You may not feel anything, but the little worm definitely will.

Second, divide the bed every three to four years—and check rhizomes carefully before replanting. Crowded iris beds are a sure target for borers.

Third, sanitation. Keep weeds pulled. After a hard frost, cut foliage down close to the rhizome. That way, you eliminate places where the moth can lay eggs.

Although bearded iris take a bit more work, well-grown plants will reward your efforts with the enchanting blooms and fragrance for which they’re justly celebrated. Learn more about Bearded Iris Care.

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