re: rot and ontario?


I thought that I would add my two cents worth to the rotten discussion 
going on! :> Especially as I too live in Ontario.

There is, as Dave Silverberg says, a distinct difference in the types of 
rot out there. Winter rot and bacterial (stinky) rot. I will address the 
first, winter rot. This is a paticular problem where I live as we get 
quite cold winter weather (periods down to 0 degrees F) but very thin 
snow cover. The lack of snow cover is part of the winter rot problem as 
the exposed rhizomes are alternately frozen and thawed by the sunlight on 
them and become split open or get damaged on the "crown area",(area where 
the leaves come out of the rhizome) 
causing what I call "crown rot" visible in early spring. (ie; pull on 
the small leaf fan emerging from the rhizome and it comes off in your hand 
and the area immediately below is rotten. (but not stinky rotten) This 
is really irritating as it is usually the mother rhizome that is 
affected.(the one that was going to bloom this year!) Minor surgery is 
required at this time and I have found that scraping with a spoon and 
the 50 % Javex (bleach) treatment works quite well. It saves the plant and 
the attached increases to try again to bloom next year!!  

A solution is to cover the iris beds in the very late fall with 
evergreen boughs and or straw in order to keep the sun off the plants, 
thus reducing the chance of this type of damage occurring over the 
winter. I have noted a marked difference in the incidence of this problem 
depending on the natural winter shading of the planting area or covering the 
planting with a so-called "winter mulch" (straw and evergreen boughs). 
Heavy snow cover also creates this protective effect.     

Now, the other part of "winter kill" is that of the effect of botrytis 
which is a cool weather active fungus infection that invades the rhizome 
during those long cool autumn, early winter days. Symptoms of this are the 
grey-black fuzzy mold visible upon inspection in early spring and also 
unfortunately sometimes a completely dead rhizome having a spongy or 
cork-like texture. :< 

Prevention or minimizing this problem is one that I am working on but 
the most effective treatment at this point that I have come across is the 
preplanting soak of the complete rhizome for approx 15-20 minutes in a 
systemic fungicide named Benomyl. This provides some measure of 
protection the new rhizome for the coming cool, moist weather conditions 
that activate soil borne botrytis fungal spores which want to claim your 
nice new iris introduction! It seems from experience that botrytis invades 
the rhizome through the divisional cuts on the newly planted rhizome. 
It then slowly 
invades the rhizome during the cool, moist autumn weather until you find the 
final dead result (a spongy rhizome) in the spring. Most of the plants I 
have had this happen to were visibly very healthy growing rhizomes the previous 
August-September-October but showed up completely dead the next spring.  

Conclusion is that with some of the care and prevention outlined above this 
type of "iris problem" can be minimized. :>
Hope this helps everyone get more iris SURVIVAL and iris BLOOM!

signed "been there and done that"! but wish I hadn't, in this case!

Dr.Chris
----------------------------------------------
----------------------------------------------
Chris Hollinshead e-mail: bu336@torfree.net
Mississauga, Ontario Canada ZONE 6B
Director, Canadian Iris Society
Editor, Canadian Iris Society Newsletter
Other Mailing lists | Author Index | Date Index | Subject Index | Thread Index