February 15, 2003

Question: My five queen palms, Syagrus romanzoffiana, have always seemed a little sickly and more yellow than our neighbor’s queens. Fertilizing them never helped. These are large plants that were put in when my house was new. Last year a pest control person knocked on my door and said my queens ‘obviously’ had a fungus at the roots and that was inhibiting nutrient uptake. He treated them somehow and they greened up quickly and stayed green for almost a year. Unfortunately, over the last few months they’ve yellowed again. Any idea about the "root fungus" and how I might treat them myself?

K. Cameron, e-mail

Answer: Root disease in palms are relatively rare. I know of no study that examined fertilization effects on root diseases and I doubt there would be any effect. Successful treatment of a particular root disease will require a particular soil-applied fungicide, not fertilization. Fertilizers are used to increase nutrients’ uptake of a plant and fungicides are used to suppress or eliminate fungal diseases. Yellow leaves on palms are a sign of nutrient deficiency and proper fertilizer application is the cure. What one uses to green up palms depends on what deficient element is causing it to become yellow. For frizzle top, 1 to 3 pounds of manganese sulfate applied to the soil and 6 ounces of the same dissolved in water and applied to the top of the palm usually works. Several repeat applications will be necessary. For bottom leaves turning yellow, several applications of magnesium sulfate applied to the soil is recommended. In our soils, palms should be fertilized quarterly with a good quality palm fertilizer at the rate of 2lbs per 100 sq. feet. This should be done even if supplements of manganese and magnesium are being applied. Finally, other factors can cause leaves of palms to yellow. Queen palms planted too deeply, or in areas of abnormally high pH, may struggle to survive and have difficulties staying green.