What Is Wrong With My California Fan Palm?

Is there any apparent discoloration and wilting of the spear leaf and wilting/discoloration of the next youngest leaf, the spear leaf may be easily pulled from the bud?

Are there any necrotic translucent blotches on the leaflets, symptoms appear on mid-canopy to older leaves?

Are there any spotting and rotting on nearly any part of the palm (leaf bases, petioles, rachises, blades, the apical meristem area where leaves are produced, flower stalks, roots, and possibly even the trunk)?

Are there any shiny black, diamond-shaped fruiting bodies 1/8 to 1/3-inch long by 1/16 to 1/8-inch wide on leaf blades and petioles, lower leaves prematurely yellow and die?

Do the segments in the leaf blade yellow and die in a wedge-shaped pattern, petiole and rachis have a reddish-brown, dark brown, or even black streak?

These symptoms indicate a fungal disease Bud rot. The most common bud rot pathogen is Phytophthora palmivora but it can be caused by Thielaviopsis paradoxa also. In palms with a canopy above eye level, a lack of new leaves and an open-topped crown are often the first symptoms to be observed. Severely diseased plants should be removed and destroyed immediately to limit pathogen spread. Potting mix from diseased container palms should be removed from the nursery. For mature palms, the diseased palm should be removed and the canopy region (including the bud) destroyed.

Palm Leaf Skeletonizer (Homaledra sabalella) feed on the upper and lower leaf surfaces, producing large quantities of "frass" that is often the first conspicuous sign of infestation. The tissue between the leaf veins is usually the preferred food, whereby the veins remain intact giving the leaf a skeletonized appearance. Insecticides are often not effective. Palms may be treated by washing the infested portion with a sponge or, if the palm is tough, spraying the infested areas with high-pressure water to wash away the silk mat and dislodge the relatively fragile caterpillars.

The fungus Nalanthamala vermoeseni causes the disease pink rot. Caused by a weak but opportunistic pathogen, pink rot primarily is a secondary disease that affects stressed, weakened, and/or wounded palms. High humidity and temperatures of 65° to 80°F favor the pathogen and disease development. Fungicides can be beneficial after heavy pruning to protect wounds and freshly cut, immature tissue, or both, or temporarily to protect stressed palms in unfavorable environmental conditions.

The fungus Phaeochoropsis neowashingtoniae causes a common foliar disease called the Diamond scale. The best option in areas where the disease occurs is to replace the California fan palm with diamond scale-resistant species of similar habit, such as the Mexican blue palm, San Jose hesper palm, Guadalupe palm, Australian fountain palm, Chinese fountain or fan palm, Chinese windmill palm, and pure Mexican fan palm. Keep existing California fan palms as vigorous as possible by irrigating regularly, especially in the summer and during winters with little rainfall. Fertilize regularly to encourage rapid growth.

Petiole and rachis blights are fungal diseases that cause the petiole and the rachis, and then the entire leaf to die. These diseases can be caused by several fungal pathogens. Because fungal spores are probably the primary methods of disease spread and high humidity is likely an important factor encouraging disease development, sanitation and water management are critical in managing these blights. Removal and disposal of affected leaves might be a means of reducing disease spread to nearby palms. On smaller palms avoid overhead irrigation. Maintain palms in optimal cultivation and health as described earlier.

This palm is susceptible to lethal yellowing disease and should not be planted where other palms are suffering from this always fatal disease. Lethal yellowing is a systemic disease caused by a phytoplasma transmitted by a planthopper. Palms with greater than 25% leaf discoloration or a dead apical bud due to lethal yellowing should be removed. Management of lethal yellowing includes trunk injections of oxytetracycline HCl (OTC) every four months and planting of palm species that are not hosts of lethal yellowing.