Expert: Long Island Gardener - 8/5/2008

Question
What is the powder or solution that is to be applied to the Iris root once it's been cut, to prevent mold & fungus from growing on it's foot?

Answer
Emmy, Irises are not prone to Mold or Fungus.  The most common problem -- and a serious one -- is the Iris Borer, which leaves big, prominent holes in the rhizomes that you would discover when you divide them.

Root Rot happens, but it's almost always caused by overwatering, occasionally by poor drainage conditions.  This, too, is something you notice when you lift them for routine dividing.  You cut the black, infected tissue out, and then you have a few options.  You can dust the wound with Sulphur.  Or you can do what Daffodil pro's do when they divide Daffodils: dip the Rhizome in undiluted Bleach, and let it dry on the counter.

Other Fungus diseases are unusual in Irises but not unheard of.  Sclerotium rolfsii -- 'Crown Rot' -- kills leaves from the top down.  When it gets to the base, it moves into the Rhizome and rots it.  You may see a network of White threads covering the crown, where the stem joins the roots.  The Fungus itself is quite common in Soil, so it needs an opportunity to attack.

Botrytis is another common Fungus, and it will, once in a blue moon, be found on Iris rhizomes, causing severe rot.  The most effective treatment for Botrytis is to toss the infected plants and wash your hands thoroughly to make sure you don't spread any of these diseases around.  Believe me, they can and they will.

THE LONG ISLAND GARDENER