I sat in on a presentation by Mr. Donald Hodel, an environmental horticulturist from the University of California Co-Operative Extension at UC Davis. He discussed best management practices for palm diseases, specifically Pink Rot, Fusarium Wilt, Sudden Crown Drop, and Diamond Scale. I’d like to share some of the highlights from that presentation here. I’ll discuss each disease individually and then cover general best management practices at the end.

Pink Rot

Pink Rot is an opportunistic disease that attacks weak or stressed palms. Palms lack the ability for secondary growth, which means they are not able to repair damaged tissue. This makes them more susceptible to diseases such as Pink Rot when damaged or pruned heavily. Various species of palms are susceptible to the disease, including many popular varieties found throughout Southern California, such as California Fan Palm (Washingtonia filifera), King Palm (Archontophoenix cunninghamiana), and Queen Palm (Syagrus romanzoffiana). The pink spores are often visible and can be found at the area of infection. This disease can attack any part of the plant including the trunk, but most often affects new growth.

Management Practices for Pink Rot

Selecting the right plant for your location is key. California Fan Palms (Washingtonia filifera) are native to the deserts of Southern Californian. They don’t do well along the coast, so don’t plant them there. Plant at the right time. Don’t plant palms in the middle of winter. Proper cultural care is crucial. Water and care for your palms properly. Avoid wounding the palm. An open wound is a perfect opportunity for Pink Rot to attack. Fungicides can be used to suppress the disease, but the cause of the stress has to be addressed to completely control Pink Rot.

Fusarium Wilt

Primarily attacks Canary Island Date Palms (Phoenix canariensis). It is a vascular disease which means it attacks the plants ability to move water and nutrients through it’s system. There are forms of Fusarium that are species specific. It’s primarily spread by pruning tools. There is no cure for the disease. It is 100% fatal; however, it is nearly 100% preventable through the use of safe pruning practices. When infected, the lower leaves die back as the palm dies from the bottom up. The fronds will often die on only one side. While this is a good indicator of Fusarium, it’s not always 100% accurate as other diseases may cause similar symptoms.

Management Practices for Fusarium Wilt

Prevention is important because there is no cure. Don’t use chainsaws to prune because they can cause large open cuts that are susceptible to disease. Prune with a hand saw instead and disinfect the blade between trees. Remove diseased palms as soon as possible since once infected, the disease is 100% fatal. Avoid spreading the soil or replanting the same species in the same location as a previously diseased tree, since Fusarium may be present in the soil. Control water runoff as it may carry the disease to a new location and infect other trees. Control trunk and root debris. Saw dust was collected in an experiment during the removal of an infected plant. They were able to grow Fusarium from the saw dust in a petri dish. Saw dust blowing around during pruning could potentially spread the fungus to adjacent palms.

Sudden Crown Drop

Sudden Crown Drop primarily affects both the Canary Island Date Palm (Phoenix canariensis) and to a lesser extent Date Palm (Phoenix dactylifera). As the name implies, this disease causes the crown, or top of the palm, to just suddenly topple over, often with little or no warning. This is potentially dangerous and people have been killed in the past from falling debris. At first look, the crown appears normal. The trunk decays internally, and it’s not until you look at the cut away sections that you can see how the disease chokes the plant. Infection is typically caused by excessive pruning.

Management Practices for Sudden Crown Drop

Once again, prevention is key since no cure is available. Management practices are similar to what was previously mentioned for Pink Rot and Fusarium Wilt including proper selection and cultural care. Do not use chainsaws or spikes. Disinfect hand saw blades between trees. A mallet can be used to tap the trunk and listen for areas of decay.

Diamond Scale

Diamond Scale is a fungal disease and not an insect as the name may imply. It primarily attacks California Fan Palms (Wasahingtonia filifera) and usually only those located in areas of marine influence. The fruiting bodies are black in color and diamond shapes. They look similar to scale, hence the name, and are found on the leaves.

Management Practices for Diamond Scale

There is no chemical control for Diamond Scale. Don’t plant Washingtonia filifera near the ocean. Use Mexican Fan Palm (Washingtonia robusta) or Guadalupe Palm (Brahea edulis) as an alternative in coastal areas.

Summary of Best Management Practices for Palm Diseases

Proper planting/transplanting is important in reducing stress to palms. Don’t plant during the fall and winter months. Don’t plant palms too deep. Practice proper cultural care methods. Don’t over-water and make sure to provide good drainage. Avoid causing wounds by not using chainsaws or spikes if possible. Practice good sanitation by properly removing and disposing of debris. Most importantly select the proper species for the location.

The above material was based on a presentation by Donald Holden. For further information please see the article “Palm Diseases in the Landscape” by Mr. Holden.  West Coast Grounds Maintenance is a commercial landscape contractor serving the Los Angeles and Orange County areas. If you have any questions we can be reached at (800) 339-2102 or by email at info @ wcgminc.com. If you would like a quote for services, please fill out the quote request form on our Contact Us page.