Black Sooty Mold on Plants, Revisited...A Solution

Black Sooty Mold on Camellia Leaves

I addressed black sooty mold not so long ago in another article; however, a few instances in the last months of last year caused me to revisit this issue.

I can do my best to recall all I've learned and then study more, yet the plant world is ever-changing in its given region.

Not that this be the case in hand, but most black sooty mold I have experienced had been on large-leaf shrubs, typically understory plants surrounded by larger shrubs or trees in areas with little airflow.

Last fall I had several customers with plants in open, airy, well-sunlit areas which were inundated with black sooty mold. All were crepe myrtles. Don't be alarmed if you have one or more on you property. Crepe myrtles are hardy and deciduous plants, which is a plus in this case.

Black sooty mold is usually found on the tops of leaves, the cuticle. It has a sooty, almost fuzzy, crusty or even slimy texture and is the result of fungus which feeds on the honeydew (excrement) left behind by aphids, whiteflies or scale. (Assholes, literally) There are other suspects as well which you or someone else may not notice unless you or they are in the right place at the right time. It is amazing how much excrement such tiny creatures can produce as they enjoy the liquids of your plants they suck from them. Then again, this is testament to how much plants transpire and respire all they need and what they don't use.

The good news is:

• The problem is only foliar, not systemic.
• The suspects don't usually suck enough of those nutrients from your plant to cause its demise, although it may kill leaves, cause much ugliness and leaf drop.
• If the plant is deciduous, the problem (not necessarily the residue left behind on the bark) will go away when the plant naturally drop leaves.
• You can remove the black sooty mold, but it may take more work than you wish to do on a Sunday afternoon...more in a moment.
• There is a (systemic, yes) solution...at least my customers say so. And, from what I know, it should work...more in a moment.

Black Sooty Mold on Crepe Myrtle

The image you see is an infected crepe myrtle on one of my customer's properties.

This is nowhere near the coverage I experienced on another customer's property, whereas it covered nearly ten feet of the tree. The surrounding jasmine, pittosporums, ivy and other plants were not grateful one bit for the gift they had received. All were severely blackened, unattractive, but still living. I just worked on them all last week.

You can easily identify black sooty mold by being able to scrape it away from the foliage and it can be removed by using a mild soap (not a detergent or degreaser), letting the soap solution remain until it loosens/breaks up the mold and then rinsing with water. A little pressure behind the water (not your pressure washer) and perhaps a little hand-to-leaf combat may be needed.

This is quite arduous, but the best approach, if you notice the culprits before such occurs, is to apply a natural oil, such as neem oil, to the leaves, but it most likely won't prevent them from returning. (This does work well on white mildew...more in a moment.)

Sometimes, we need to go with man-made prevention.

I have two customers who use BioAdvanced Tree and Shrub Protect & Feed and they are pleased with the results. It was established in the U.S. by Bayer. The active ingredient is Imidacloprid, which is a neurotoxin and is safe for most applications (Read label instructions.) when used properly and is actually used for pest (mainly fleas) treatment on animals. Be mindful around bodies of water with invertebrate fish. And if you are a honey bee keeper, don't spray it in your hive. Seriously, please read the label instructions. I don't want to write another article on the so-called global bee decline.

Mold versus Mildew 

No one wants either, mold or mildew, in their home, on their plants or in their lives. Either one, typically spawns, grows and enjoys moist conditions. 

Without much detail; mold is typically black or green, growing upward and downward, often corrupting or infecting its host while mildew is usually white and remains aligned with the surface of its host.

Mildew is a type of mold, often called, "Pre-stage mold". To learn more, please go to https://molekule.science/mildew-vs-mold-difference/. 

On plants, I usually find white mildew on the underside of large leaf shrubs, such as sasanquas, in areas with poor airflow and limited sunlight. For these situations, I usually apply neem oil, perhaps twice and then remove with high pressure water and perhaps by some hand cleaning.

A common error is to confuse white mildew with scale. White mildew will usually spread white residue and not feel course if rubbed with your thumb, while scale will feel more course and not show any residue. If you have good eyesight or have a magnifying glass, you can look at the leaf in-line with its edge (margin) and will notice some elevation above the leaf surface.

This would be scale, a pest, which may produce black sooty mold over time, perhaps not much time. I don't know. I have seen plants without black sooty mold look completed covered in several weeks.

Hey, this is not an exciting topic, but it may help you have a healthier and prettier landscape.

If you need help with this or any other aspect of your plants, please contact me.

Doug Ingbretsen

803-553-5757

service@back40.us