Extension Service: New mystery ravages, kills queen palms

So far I've heard of several communities in Collier and Lee counties that have lost 10 to 15 queen palms in the last six months. These include Calusa Bay, Pelican Landing and Colonade.

So far only queen palms are affected. Since December 2004, Monica Elliott, plant pathologist with the University of Florida in Fort Lauderdale, has examined queen palms from Tampa to Orlando to West Palm Beach to Naples. All sites have a similar sequence of palm decline.

Symptoms were first observed a year or two ago on established palms, but fewer than 1 percent of the queen palms on a property were affected, so not too much was thought about it. Now, some communities have lost up to 10 percent of their queen palms.

Elliott has released an update as of May 5 that can be seen on this site:

flrec.ifas.ufl.edu/Hort/Plantpathology/plant.htm

Here are her findings:

The symptoms are as follows. The lowest (oldest) 2-3 leaves turn brown but do not break or hang down. The next 2-3 youngest leaves in the canopy will turn varying shades of yellow. The yellowing leaf symptoms alone are not indicative of the disease, as these symptoms would be similar for natural senescence, especially when potassium deficiency is present. What makes the disease different from natural senescence is that usually within two months of initial symptoms, the entire canopy has turned brown, as if freeze-dried in place. The leaves do not break nor do they hang limply parallel to the trunk; they simply turn brown in place within the canopy.

Closer examination of the yellowing leaves and the next green leaf in the canopy should reveal what we believe is the initial target of the pathogen, the leaf petiole at the point where it is bending out of the canopy. We have observed initial areas of discoloration (a brownish-red 'streak') at this point that then seem to spread in both directions on the petiole, toward the trunk and toward the leaf tip. The petiole is not rotted, but simply discolored. Cross-sections through the petiole reveal internal discoloration. Cross-sections must be done with a sharp saw and not with a crushing tool such as a clipper, as the crushing motion will discolor tissue also. Leaflet tips, even on lower green leaves, exhibit drought symptoms.

The bud of the palm is not killed until sometime (probably a week or so) after the canopy turns brown. When cross-sections are made through the crown of a dead queen palm, the bud is still clean and white, but older leaf and inflorescence bases are discolored and usually rotted. The symptoms and their development suggest a pathogen, probably fungal, that is producing a toxin.

The pathogen is unknown at this time. We have isolated "potential" pathogens and will shortly be conducting pathogenicity tests.

For now, the only thing we can say is, that it is a new disease of queen palms. Since we do not know the pathogen(s) causing the disease, cultural or chemical management recommendations cannot be made.

Unfortunately, quite a few communities have a monoculture of queen palms. These palms are considered high maintenance with their high pruning requirements and several existing risks which, if not addressed, will kill the palms. These risks include ganoderma butt rot disease; potassium deficiency; frizzletop, a manganese deficiency; and boron deficiency. See this site for more information:

collier.ifas.ufl.edu/Horticulture/queenpalm.htm

Now there is another killer disease that could put a bigger hole in our landscapes. It is not recommended to replant with queen palms until more is known about this disease. Remember to diversify your landscape with several species of featured trees and palms so that if an epidemic hits, you will still have some plants standing.

Doug Caldwell is the commercial landscape horticulture extension agent and landscape entomologist with the University of Florida Collier County Extension Service. E-mail: dlcaldwell@mail.ifas.ufl.edu. Call 353-4244, ext.203. For updates on Southwest Florida Horticulture visit: collier.ifas.ufl.edu

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