Question
QUESTION: Hello, I have a bad case of black leak fungi on my Quaking Aspen tree and am currently treating it with a mycorrhiza fertilizer. Does this stuff kill the fungi or just control it? Also the branches of this tree have all turned a flat black color while the trunk has kept its nice whitish healthy appeareance. Is their a different problem now? I planted it in early March and the tree has gotten plenty of sun/water and looks to be growing rapidly and healthy. It is a tree that I dug out of a small Aspen stand locally near my house. I live in the Northeast(NH). Please send any advice on these symptoms.  MIKE

ANSWER: Mike:
You may be referring to a condition called sooty mold.  This is a group of dark colored fungi that grows on the excretement of insects (aphids, scale etc.)and produces a black covering/layer to the leaves.  It can be rubbed off with a wet paper towel or finger.  Controlling the insect is the solution to preventing the sooty mold.  Sooty mold is not considered a plant disease problem- it is an indication of an insect infestation.
There are other various leaf spots on poplar and aspen that may give the leaves a dark appearance.  Spraying a fungicide as leaves emerge in the spring can help, but usually the tree is to tall to be a cost effective practice, so we usually recommend just raking up the leaves during the winter OR just before spring and destroying them (burning is good if allowed by your community)because many of the leaf spotting fungi can survive on those fallen leaves over the winter to cause the return of the disease in the spring. Raking an burning fallen leaves is quite helpful and a lot less expensive than spraying 2-3 times during the spring.

The mycorrhizal fungi are associated with the roots of many of our plants and function primarily in "boosting" plant health by increasing the surface area of the plant roots and aiding in the absorption of certain nutrients which in turn reduces stress.

Regards
Steve

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QUESTION: Steve, Thanks for getting back. Would sooty mold cause the branches to darken to a flat black? I have not noticed any insects (Aphids or Scale) on or around the tree. The black spots and dark appearence on the leaves/branches look like an internal problem. What's the best method to kill sooty mold besides spraying fungicide?

ANSWER: Mike:
See if the black stuff will wipe off with a wet paper towel or wet finger (use a bit of elbow grease on it!).  If it does come off on these objects, then more than likely it is sooty mold.  We do not use a fungicide for sooty mold.  We use an insecticide for the insects that cause the sooty mold.  Best to get an accurate ID on the insect before buying/applying an insecticide.  Bayer Advanced Garden Insect Control for Trees and Shrubs can be applied to the soil and roots will take it up.  It may take 30-60 days to do this.  If you are dealing with an insect for sure, then you might consider the Bayer product and put it out in the spring when new leaves are starting to form.  It comes in a blue plastic bottle at your garden center or Lowe's or Home Depot home improvement center. It is a concentrate and must be mixed w/water before applying- see the label.  It is not cheap either, so be sure you are dealing with a bug first. If it is an insect and you are able to control it, then the black stuff will eventually come off the plant surfaces, but if the insect is not managed, then that black stuff will continue to build up. Besides making the plant look lousy, the sooty mold doesn't do too much harm unless it builds up on the leaves blocking sunlight absorption.

Again, first thing-find out if it is sooty mold, then get an ID on the bug, then start your plan for an insecticide if you want to go this route.

Steve

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QUESTION: Steve, Yes the black mold does come off with a wet paper towel, but only in certain ares of the tree. Mainly on the smaller, more flexible branches. I also noticed an infestation of scale that I was not aware of. In some spots the scale have already burrowed into the wood itself. I did not notice any aphids but I could be wrong. What is my next step??

Answer
Mike:
As mentioned, rake up and burn (if your community allows it) fallen leaves and twigs sometime just before spring gets here, then try the Bayer product mentioned above. It contains a systemic insecticide called Imidaclorpid (sp). Mix and apply according to the label. Unfortunately, when scale insects do die they often remain on the plant and do not fall off- so it is hard to tell if they die.  You may just have to monitor their presence to see if they increase or not.

Regards
Steve