Judging a book by its cover can cause some very expensive mistakes

SITUATION: You find Ganoderma conks at the base of a palm. You surmise that you are looking at a palm that is definitely on its way to an early death. Is this a reasonable conclusion? Yes, but is it always true? No, it is not always true; there is a chance that you may be mistakenly judging a book by its cover. Ganoderma zonatum is a plant disease that is pathogenic in palms. Most landscape professionals?and palm enthusiasts in Florida will have heard of Ganoderma and may also be aware of its markers?and of the symptoms it produces in an infected palm. If you are not familiar with this disease, the link at the end of this discussion will take you to some information about it. As has been previously discussed, once a palm is infected with Ganoderma zonatum, it cannot be saved. The disease is translocated by spores that are produced on the rather unique looking basidiocarps (also commonly referred to as “Conks”) that develop on the trunk of an infected palm during the mid-stage of infection.?The spores are from the undersides of these conks and can move around on the wind. They can also be moved by people, birds, animals and anything else they might come into contact with to hitch a ride to another location. All palms are susceptible to Ganoderma; field observations tend to indicate that palms with a rough, fibrous trunk surface become infected more commonly then palms with a smooth trunk surface but any palm can contact this disease. The fact(s) that all palms are susceptible, the disease is untreatable and the spores can move around very easily cause horticulturists to recommend the immediate removal of a palm on which a conk is discovered. As with almost every issue in our living environment, professionals have various opinions of the need for immediate removal but what is not in question is the need to remove the palm at some point. Personally, I believe that people only buy palms to look at them and while a palm looks good it is delivering good value. I further believe?that if one can undertake a fairly simple procedure to eliminate the risk of disease translocation, so long as the palm is delivering good value it does not make sense to immediately remove it. In any case, the common reaction to the presence of a conk on the trunk is often knee-jerk and it can result in the loss of some very expensive palms that were never in danger to begin with. Wait a second; the palm has one or more conks at the base and close examination determines that they are indeed Ganoderma. We know that Ganoderma is not treatable and that infected palms are certain to die. How is it possible that a palm in such a condition may not be in danger?

Amongst the community of Landscape contractors, a little known fact is that Ganoderma zonatum is not the only species of Ganoderma living in the southern US but it is the only species here that is pathogenic to palms. There are other species of Ganoderma that live here and produce a shelf-like conk which is almost identical in appearance to those produced by G. zonatum. These conks might be found growing on woody tissue at the base of a live palm or, in the case of a multi stem palm like an Areca or P. reclinata, growing on the dead, woody base of a stem that had been cut off at some time in the past. These look like Ganoderma because they are Ganoderma but where you find yourself looking at the evidence of the disease in the form of the conks but see no evidence of weakness or discoloration in the canopy of the palm, before you tell the client that the infected palm needs to come out, slow down just a moment because you may be looking at non-pathogenic Ganoderma. I can attest to the reality of this because I have observed it myself. I was called to a client’s house to inspect a stand of Areca Palms that the Landscape maintenance personnel had observed conks on. Areca’s are well known hosts for G. zonatum infection so hearing that these were infected was not at all surprising and in fact, the commonality of the disease’s activity in this species tended to predispose me to believing that these were infected and would die.

I came to the site, went into the stand and examined the bases of each of the clusters. I found basidiocarps that were obviously Ganoderma and I quickly decided that the palms needed to be removed because there were quite a few conks spread out in the bases of many of the palms in the group and disease translocation would have been far too difficult to control. When I came out of the stand and stood looking at group and talking to the owner’s rep, I realized that none of the stems in any of the palms appeared symptomatic and that was weird. None of the fronds on any of the stems in any of these obviously infected clusters were demonstrating any symptoms common to a palm that is infected with G. zonatum. I began thinking about the conks themselves and went back in for another look; they were obviously and most certainly Ganoderma but at that point I noticed that they were not quite right. The color was off a little, they were a little small for mature G. zonatum conks and the leading edges of the basidiocarps didn’t look quite right to me when picturing G. zonatum conks I had seen so many times in the past. The owner was ready to have the entire stand of Arecas removed immediately because she has many other palms on the property including some very large, very valuable Canariensis; she would happily sacrifice this stand of Arecas if it meant ridding the property of a disease that posed a big risk to all of the other palms but the more I thought about it, the less convinced I was that this was Zonatum.

Previous to this encounter I had never seen nor heard of other any other species of Ganoderma on palms but I knew there were others in Florida and I had seen some of these hosting on dead wood. I gave the whole scenario more thought; I wasn’t able to balance the presence of the conks with the perfect condition of the canopies on the stems and I decided to stop the removal, temporarily anyway. I harvested some samples of the basidiocarps and then sprayed/drenched all of the others with chlorine bleach to destroy the spores and spore producing tissue thereby temporarily eliminating the ability for the disease to translocate and I told the owner that I believed it to be possible that what we were seeing was a different species of Ganoderma that wasn’t pathogenic to the palms. The landscape maintenance guys were looking at me like I had lost my mind and were insisting that it was Ganoderma and that they had to remove the palms right then. I wasn’t sure; I just wasn’t sure but it felt right and those Areca’s were fully mature and gorgeous; I just couldn’t wrap my mind around the utter lack of symptoms in the canopies of Ganoderma infected palms with multiple conks. I know my way around palm trees pretty well and the owner trusted my judgment so the Arecas stayed in and I sent the conk tissue off to the lab. When the results came back they confirmed that this was a species of Ganoderma that was not pathogenic in palms. Upon close examination it became clear that though the conks were growing all around the bases of the stems, they were not growing from any of the living trunks themselves but were instead hosting on woody tissue left over from stems that had been trimmed out long ago. For the maintenance contractor this was a classic case of judging a book by its cover but who could blame them? The site personnel observed the conks, they looked like what they are so they correctly declared them to be Ganoderma and then informed the owner that the disease would destroy the Arecas and spread to other palms on the property if the Areca palms were not immediately removed from the site. Given that none of us had previously seen conks on palms that were not Ganoderma Zonatum, their identification & conclusion was reasonable, it made good sense and it was, in this case, wrong but like I said, who could find fault with this misdiagnosis? I applaud them for having seen and reported the conks at all; unfortunately that doesn’t happen all that often – these guys were on their toes, they were dedicated?& interested and they kept their eyes open. They were acting in the best interests of their client and they would have been right 9 times out of 10 and this was that 10th time. Fortunately the truth of the matter was revealed before the palms were removed; we were able to avoid the destruction of some beautiful material and had learned something new in the process. That is one of the most exciting things about our industry, there is always something new to learn and this was a great lesson for all of us. It would have been really easy to just let the obvious take command but we can only teach ourselves new things by challenging convention and in this business, where something just won’t balance, you need to figure out why if you really want to get it right. Most of the time Conks such as these will be Ganoderma Zonatum and immediate steps should be taken to limit disease translocation until the infected palm(s) can be removed but if you have mature conks and the canopy looks perfect, step back and flip a page or two, the cover of that book may not be telling you the whole story.

George P. Nottingham

President

Groundworks of Palm Beach County Inc.