I am at a loss, I have black soot on my Crape Myrtle. What can I do about this that might be a organic alterative.
black soot
See if you have aphids on the same plant. Often the honeydew from aphids is what the black sooty mold grows on. Blast off the sooty mold with soapy water along with the aphids. It will help some this year but next year it will be gone until aphids attack again.
No aphids or bugs of any kind......that was the first thing I checked I know that's usually the reason for black soot..... should I add a little bleach to the water or would that burn the plant?
I would think that the amount of bleach or some chlorine type product that you'd have to add to get results would likely harm the plant, especially if the weather is as hot as it has been of late, not to mention whatever is growing under that crepe myrtle. And then, you'd have to make sure that you covered the entire plant including tops and bottoms of all leaves and THEN you'd be wise to wash it all off after it sets for a few minutes. The soapy water solution works at times so that may be your first step...
Personally and barring any type of aphid infestation, I'd think try some type of fungicide first (ask a knowledgeable local nursery for correct brand or type). Note that I'm not a big chemical user but there are those times when it's still the best solution.
As a side note, I remember reading last summer that there was an attack of some new species of aphid that was attacking crepes in mass and the entomologists were trying desperately to find a solution, either natural or chemical. Haven't heard an update so that may be a non issue by this point.
On the other hand, sooty mold on crepes is a regular and yearly occurrence and it would have to be pretty bad to affect the plant's overall growth. Ugly yes, harmful? Not that much... JMO
Steve
Black sooty mold won't hurt it - just looks terrible. I wouldn't use bleach either (or even a fungicide). Seems like the general consensus is to get rid of the pest causing the honeydew that makes black sooty mold grow. Try some Neem oil if you want to spray the plant.
http://www.gardeningknowhow.com/plant-problems/disease/how-to-get-rid-of-sooty-mold.htm
http://baker.ifas.ufl.edu/Horticulture/documents/BlackSootyMoldonLandscapePlants.pdf
http://www.ces.ncsu.edu/depts/ent/notes/O&T/houseplants/note41/note41.html