Arbor-wellness: Diamond Scale

Diamond scale is a fungal disease found exclusively on certain palm trees. The name causes a bit of confusion, as the term “scale” usually refers to scale insects. Diamond Scale is an actual fungal disease that is normally a relatively mild disease that rarely causes the death of the palm. However, it does make infected palms look unsightly and predisposes them to other diseases which may be lethal. It derives its name from its characteristic diamond-shaped fruiting bodies.

Diamond scale attacks primarily the California fan palm in coastal areas and in inland areas subject to coastal influence. The drier climate areas of California rarely see it. It does warrant treatment when found in coastal areas, because it us usually indicative of a palm in poor health. Besides treating for the disease, keeping palms healthy and vigorous helps keep the disease in check.

I have black odd shaped spots on my fan palm, what is that?

That is a disease called Black Diamond Scale”. It is common on California fan palms in areas with coastal influence.

Will it kill my palm?

It won’t kill your palm outright, but it weakens the palm and makes is susceptible to other diseases that may be fatal. If your palm is not growing fast enough, it will build up in large numbers on old fronds, making it quite unsightly.

Will it spread to my other palms?

It seems to only affect California fan palms and palms that are crosses between Mexican fan palm and California fan palms. The pure Mexican fan palm and most other species aren’t affected by it.

What should I do about it?

There are several steps that are important to take:

First consider pruning the older fronds out annually. This lessens the problem, but be sure to dispose of the fronds off site and don’t prune healthy palms with the same equipment unless you sterilize the equipment first.

Second, make sure the palm is growing adequately. Palm are heavy feeders and should be fertilized with specialty fertilizer twice a year in most cases. Also make sure there is adequate drainage and that it is properly watered.

Lastly, treatment should be considered on a regular basis until the palm recovers and is healthy. Your Arborwell Arborist can recommend a program to help your palms stay healthy and disease free.

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