Bacterial Rot in Irises

Icky-smelly-deadly!

By:  Bonnie J Nichols

Texas has had 12+ inches of rain and counting……..the weather is cooler and the days are shorter.  What is that icky smell in the garden?? 

The rain, while refreshing our lakes and absolutely necessary for all living creatures – can be a not-so-good thing for our bearded irises.  The tall bearded irises seem to be more impacted than the smaller irises such as Standard Dwarf (SDB), Intermediate (IB), and border bearded (BB) – however, not exempt from rot.

Bacterial rot can happen no matter the temperature.  Bearded irises do not like a prolonged period of time with their roots and/or rhizomes soaked with water.  Rot can happen quickly and can be deadly for irises. 

Be observant!  While our neighbors might think we are “a bit” strange slowly and carefully looking at nothing but green irises leaves and not a bloom in sight – the earlier we can attack rot, the better our chances are of saving the rhizome.  The outer leaves may turn yellow or the entire fan may be laying on the ground – these are definite signs of rot.  The smell of rot is very unpleasant – okay, it is downright icky!  Push on the top of the rhizome.  If rot is present, the rhizome will be mushy.  Sometimes maggots or small worms are already present. 

If you find rot, you can dig the infected rhizome.  Digging this late in the season might be problematic to dig the rhizome and get it re-established before winter.  Irises need about 6 weeks to establish new roots.  Whether you dig the rhizome or not, you must clean out all the infected tissue.  You can use a sharp knife to scoop out the rot. THROW THE ROTTED tissue away!  Do not leave it in your flowerbed.  DO NOT reuse the knife until you have thoroughly cleaned it with soap and water.  Once the rot has been removed, you can apply several types of products that may work to stop the rot. 

For the last few years, we used DIAL (not the store branch) antibacterial soap.  The irises have either built up a tolerance to the soap and/or the manufacturer has changed the formula, because last year I had limited success stopping the rot with the soap.  Another product you may try is BARTENDERS FRIEND, ZUD, or COMET applied directly to the area you removed the tissue from.  When the DIAL soap was not working for me I researched for an older product than many of us used in the 1980s.  We used AGRISTREP.  You cannot find the product any longer.  I researched the active ingredients of AGRISTREP and found that Fertilome Fire Blight Spray has common ingredients.  Finding the product on store shelves is difficult and only a handful of stores carry it.  I found it online through Amazon – buying one 2 oz container at a time.  NOTE:  There may be generic products on the market.

To purchase through Amazon is about $12-$14 per 2 oz.  You apply the product directly on the infected area.  NO NOT dilute in water.  You may have to apply multiple times (2 x per day) for a few days.  I know the product is expensive; however, so was the $60 for my “favorite” new iris purchase.  I found the Fertilome product at BWI through our nursery license.  Wholesale, the product is appx. $10. 

Happy gardening.  Don’t give up on the irises.  They just need our help getting through the monsoon season to bloom for us in the spring.