The Q&A Archives: Iris Corm Rot

Question: It is early July & I have found rotting iris corms. It seems too early to dig up and divide the whole, large bed.Can I just dig up the part I have found & throw it away ? Then how do I treat the reminder so that it doesnt spread ?

Answer: It is a good idea to remove any diseased foliage and rotting rhizomes from the bed immediately to try to limit reinfection. You may in fact find that the rot is the result of borer activity or poor drainage or poor air circulation or a combination of these, so do try to remedy any of these as well when you lift and divide the plants. Keeping the plants well weeded and dividing them often to avoid overcrowding, planting them in a rich soil that is well drained and in a full sun location with good air circulation all help avoid problems. Checking the plants for and controlling borer infestation will also go a long way toward stopping bacterial soft rot, as does avoiding injuring the rhizomes by careless weeding or clipping. Finally, though, some iris just seem prone to it and in those cases there is nothing that you can really do to prevent it except grow a different variety.

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