Is this spotting on my schefflera houseplant caused by alternaria?

Question

I've had a medium-sized schefflera or 'umbrella' houseplant for about five years now, and it might have been as old when I first got it. Lately, I have noticed black spotting on some of its lower leaves - the leaves higher up don't seem to be affected. The affected leaves are slightly sticky.

My question is twofold. First, is this caused by alternaria? Second, what is the best means for dealing with it? I'm reluctant to use any sort of fungicide or bactericide as I have two cats that are fond of this and other plants. Can it be controlled with removal of the affected foliage, limiting the moisture of the soil, and ensuring that the remaining foliage is kept dry?

As a bonus, I also encountered some small yellowish growths of what appeared to be a fungus on the surface of the soil a few months ago. Whenever I saw it, I would scrape it off and dispose of it, but it kept creeping back. I can't provide a picture, as it now seems to have departed, at least for the time being. Could this be related to the spotting of the leaves, or share a cause (overwatering)?

Answer 1

I believe this is scale who exude a sweet sugar. It falls from them onto the leaves below and the fungus are growing on the sap. However, to be sure, let's do the detective thing:

• can the black spots be removed by wiping with a clean cloth?
• if they cannot be removed then it is likely that they are caused by a fungus/virus/bacteria due to over watering.
  • Solution: change watering habits to allow at least the top inch of soil to dry out before watering again
  • OR reduce watering and cut back the plant hard and wait for regrowth
• If they can they are not a plant disease caused by a fungus/virus/bacteria as those grow inside the leaf tissue.
  • examine the underside of the leaves for small round bumps
  • look for sticky sap areas on the leaves that are lower down
  • Solution: use soap and water as described here. Apply three times at five to seven day intervals. Use a cloth or paper towel and rub all leaves and stems to maximize coverage
  • OR the take no chances solution: cut the plant back hard and apply soap and water. When you only have a few stems it is a lot easier to control scale. Scheff's bud out readily even from old wood so cutting it back is not a permanent change

From your comments I looked at what you call soil fungus. This is perlite that has discoloured due to dissolved mineral salts in the water. It is not a danger to the plant. You can remove it or leave it be. Top dressing with more soil less potting mix is always a good idea.

I also looked at the trunk fungus and this is part of the normal bark growth. Sometimes these plants exude a sap at the site of a mechanical injury and it is normal to see bumps which are areas where adventitious roots can grow from if the humidity is high or the plant is cut back.