Three Important Diseases of California Palms

Palms are certainly iconic components of the California landscape, and they make great additions to most residential and commercial properties in our region. Several palm species are suitable for the local climate, and most require relatively little maintenance or pruning.

However, the palms in our area are threatened by a number of different diseases, which can cause your palms to languish or die. We’ll talk about three of the most notable diseases that threaten palms in Southern California below.

Pink Rot

Pink rot is a disease that can cause problems for most palms grown in California, including queen (Syagrus romanzoffiana), Mexican fan (Washingtonia robusta), California fan (Washingtonia filifera), and kentia palms (Howea forsteriana), among others. The disease is caused by a fungus called Nalanthamala vermoeseni, but it usually only causes problems for palms that have already been weakened by pests, drought or some other disease.

Symptoms of pink rot – most notably including rotting and misshapen leaves – are typically limited to the crown, but trunk rot has been noted in some cases. Some trees recover, while others will grow weak over time and eventually succumb to the disease.

The best way to protect your palms from pink rot is to ensure that you care for them properly, avoid disturbing their root zones, provide adequate irrigation during dry periods, and ensure that they are pruned properly.

Diamond Scale

Diamond scale is a disease caused by the fungus Phaeochoropsis neowashingtoniae. This causes a bit of confusion, as the term “scale” usually refers to scale insects. Naming issues aside, diamond scale is a relatively mild disease, which rarely causes the death of the tree. However, it severely compromises the aesthetics of the tree and predisposes it to other, secondary pathogens, which may be lethal.

Diamond scale primarily affects the foliage of palms. The first signs of an infection usually take the form of small dark spots scattered along the leaves. Over time, these spots give way to diamond-shaped fruiting bodies (roughly akin to mushrooms), which give the disease its name. Eventually, entire leaves will begin turning brown and dying.

Fusarium Wilt

Fusarium wilt is a disease caused by the fungus (Fusarium oxysporum). It occurs in several different forms, which tend to attack a single plant species. Tobacco plants are affected by one form, while sweet potatoes are affected by another. In California, the fungus is known as Fusarium oxysporum f. sp. canariensis, and it infects Canary Island palms (Phoenix canariensis).

As the name implies, Fusarium wilt causes the leaves of palms to brown and wilt. It is usually fatal to palms, although it isn’t always the immediate cause of death. Instead, Fusarium wilt weakens the palm, which allows other diseases to gain a foothold. Accordingly, palms with Fusarium wilt often die from other diseases before Fusarium wilt manages to cause death.

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If you are worried about the health of your palm trees, or you would like some advice on the most disease-resistant species to install, give your friends at Evergreen Arborist Consultants a call. One of our certified arborists will visit your property and inspect your trees or the site you have available. He or she will then provide you will actionable advice that will help keep your existing palms looking their best or give your soon-to-be-planted trees the best chance to thrive.