Black spots on top and bottom of palm leaves

[MiamiNorm]

Hello

An in ground palm whose name I don't know has black spots on its leaves. Underneath each leaf are little worm-looking things that easily scrape off with my nail.

In the past, I've seen the paver bricks underneath the fronds "stained" in the same black as the one on top of the leaves. 

Is this a fungus and pest issue? And what can I do? 

Thank you. 

[Scott W]

Well, first off I can tell you it's not a palm but a cycad, and could be Cycas revoluta.

With that, the black stuff could just be mold or mildew.  I'd try to just rinse it with some high pressure water and dish detergent.  Is this is fun sun or shaded?

[MiamiNorm]

Thank you Scott

It gets sun for a lot of the day, and it's big and healthy. 

The cleaning may work, but what about the worm-like looking things under the 2750 leaves = a lot to clean? 

[Scott W]

I've honestly never seen them on any of my cycads.  You could try horticulture or Neem oil after you clean it and maybe a systemic as a preventive to ward off Asian cycad scale

[Merlyn]

The black sooty mold is sometimes a sign of aphids or other sucking insects.  I'd check around the leaves for any bugs or mites.  Also check to see if there are small black ants wandering around.  Sometimes ants will "farm" aphids and other insects for the sap they produce.  They've been observed picking up bugs and moving them from leaf to leaf. 

Are the small worm-looking things actual insects?  Or are they blobs of sap?  You could check them out with a 10x or 16x or 20x jeweler's loupe.  Or scrape one off onto a paper towel and see if it moves around.

[MiamiNorm]

1 hour ago, Merlyn said:

The black sooty mold is sometimes a sign of aphids or other sucking insects.  I'd check around the leaves for any bugs or mites.  Also check to see if there are small black ants wandering around.  Sometimes ants will "farm" aphids and other insects for the sap they produce.  They've been observed picking up bugs and moving them from leaf to leaf. 

Are the small worm-looking things actual insects?  Or are they blobs of sap?  You could check them out with a 10x or 16x or 20x jeweler's loupe.  Or scrape one off onto a paper towel and see if it moves around.

Thanks Merlyn

The things underneath don't move and look like egg-type things or little shells of something. I don't know 

[MiamiNorm]

An update. 

As you can see, beautiful, green, and healthy fronds arw growing above. 

Would it be wrong to cut the lower ones so that whatever the black thing is doesn't infect the new fronds? 

 

Edited May 11 by MiamiNorm

[Merlyn]

@MiamiNorm as soon as the new leaves are "hardened off," i.e. changed to a deep green and are no longer soft and pliable, then you could cut the old set off.  If it's a bug (mite, aphid, etc) that's doing it, then cutting off the old ones won't prevent the bugs from getting into the new leaves.  It might slow them down a bit, but not stop them.  If you do try something like Neem oil, make sure that you do it in the evening so the oils have time to dry out overnight.  Otherwise the droplets of neem oil can easily form a magnifying glass and burn the leaves.

[MiamiNorm]

Another update. 

We cut rhe blackened fronds, and the new ones look gorgeous. However, some have developed a yellow stain on 1 half of several of them?

Is that sun burn, iron deficiency or something else? 

 

[happypalms]

On 4/17/2024 at 3:22 AM, Merlyn said:

The black sooty mold is sometimes a sign of aphids or other sucking insects.  I'd check around the leaves for any bugs or mites.  Also check to see if there are small black ants wandering around.  Sometimes ants will "farm" aphids and other insects for the sap they produce.  They've been observed picking up bugs and moving them from leaf to leaf. 

Are the small worm-looking things actual insects?  Or are they blobs of sap?  You could check them out with a 10x or 16x or 20x jeweler's loupe.  Or scrape one off onto a paper towel and see if it moves around.

A symbiotic relationship 

[Merlyn]

@MiamiNorm Revoluta are usually sun-hardy anywhere in Floriduh.  If those splotchy areas are directly facing the hottest sun hours then it's possible.  But most likely it's a mild Manganese deficiency.  I put a handful of Manganese Sulfate on all mine at least once a year.  In Revoluta/Sagos:

• Manganese deficiency shows up on new leaves.  If it's mild then you get a few random splotches as the newest flush "hardens off."  In severe cases you get what's called "frizzle top."  Manganese is not mobile in plant tissue.  Thus the plant can't "steal" it from the oldest leaves.  If you google search "sago frizzle top" you'll get plenty of pictures.
• Magnesium deficiency shows up on the oldest leaves first.  The first sign is usually some yellow tips on the oldest fronds.  There's a supposed cultivar "Cycas Revoluta v. Aurea" that frequently grows out with yellow tips on the fronds.  IMO that's a Magnesium deficiency, because there are literally tens of thousands of "Aurea" in the Orlando area.  As an example here's a neighbor's one with 4' of trunk, showing Magnesium yellowed tips and some old hail damage:

The cure for either is a handful of Magnesium or Manganese Sulfate.  Neither can be fixed in the existing leaves, as plant tissue that's turned yellow won't ever turn back green.  But you can fix it so the next flush in late summer will grow out nice and green.