TREES, PLEASE: Queen Palms, Part II: Pests and Diseases

A mystery affliction causes queen palms’ otherwise healthy fronds to collapse.

By Tim Clancy.

In a recent article, we discussed the nutritional needs of queen palms (Syagrus romanzoffianum) and the importance of proper pruning and having a proactive fertilization plan to help keep the palms looking healthy and growing vigorously. Now we’ll focus on one of the reasons queen palms are so commonly planted, which is that they are relatively pest and disease free.

Despite queen palms’ resistance to pests and diseases, they are not without their problems. Scales often find their way onto the trunks of these trees, but I have seldom seen any significant damage caused by these insects. Look for ants climbing in and out of your trees. They “farm” the scale insects by removing the honeydew manufactured by the scale and using it as a food source. Controlling the ants will ultimately help in controlling the scale. A trip to the local hardware store should prove fruitful to those looking for DIY ant control options.

Pink rot is caused by an opportunistic pathogen (Nalanthamala vermoeseni) that affects queen palms undergoing stress. It favors high humidity and temperatures between 60 and 80 degrees. Cultural practices are the most important factor in controlling this disease. Fungicides can be used a part of a control strategy but relying on them alone will disappoint.

A kink is seen in the stem of this fallen queen palm frond.

While the signs of scales and pink rot may be recognizable, there is currently a mysterious affliction affecting queen palm fronds. As previously discussed, there are many reasons to prune queen palms and it is a common “treatment” (remember that as a treatment, pruning should “fix” a problem). Quite often, fronds left on the tree after pruning will droop or fall and you will see a kink in the palm stem (petiole). I have seen this being blamed on clumsy pruning with the contention being that the drooping fronds have been accidently cut by the person doing the pruning and the frond(s) fell later. I have never been able to confirm this and on a closer look found this not to be the case (at least on the trees I observed).

What appears to happen is that the fronds collapse (see photos). Noted palm expert Don Hodel has verified this collapse condition. I contacted Don after I observed the collapse on many trees under differing cultural conditions. He was sufficiently interested in my observations and drove down from Los Angeles to check it out for himself. He inspected several palms and confirmed what I was seeing and also opined that the collapse was NOT the fault of tree pruning activities or cultural conditions or pink rot. He collected samples to have them analyzed by University of California scientists. The results provided no diagnosis and the cause of the petiole collapse condition is still a mystery.

Queen palms, when well cared for, provide an aesthetically pleasing plant choice for your garden. Paying attention to a few minor details with regards to nutrition, pruning, pests, and diseases, can go a long way in keeping your trees happy.