Ganoderma: why a palm goes over while its crown is still green
The trunk base has been going for a long time before the crown says anything about it. What needs checking is down at the bottom, not up top.
It always sounds the same when it arrives on WhatsApp. Strong wind overnight, one palm down by morning, and the confusing part is that the crown is still green. The palm looked healthy right up to the last second. What actually happened is that it had been unhealthy for a long time, and the part that had gone was the part nobody ever looks at.
What basal stem rot is
The cause is a soil fungus called Ganoderma boninense. It attacks the woody tissue at the base of the trunk and turns it hollow, a little at a time, from the inside. What it destroys is the tissue that carries water and nutrients up from the roots, and at the same time the tissue holding up the weight of the palm.
It is not a leaf disease, and that is the whole problem. Everything you can see from ten metres away is leaf. The fungus spreads through root-to-root contact, and through the stumps and old trunk left in the ground, which can hold it for years after the old palm is gone.
Why the crown is still green
Because an oil palm can carry on for a long time on partial tissue. As long as some of the base is still working, water keeps going up and the fronds stay green. The crown only shows it once the damage at the base is extensive, and by then the palm cannot be saved.
So a palm that looks fine today may already be half hollow underneath. That is why checking the trunk base cannot wait for symptoms. Waiting for symptoms is always too late, not through carelessness, but because this is the order the disease works in.
The early signs you can still see
Three things come before it falls. The lower fronds hang slack around the trunk like a skirt, while still green. Spear leaves stack up at the top and do not open, two or three at once. And the bunches come out smaller, even though nothing about the fertilising changed.
The fourth sign is the fruiting body itself: shaped like a fan or a kidney, stuck to the trunk base or coming up out of the ground around it, white at the edge when young and glossy brown when old.
That fan-shaped body is a late sign, not an early one. By the time it appears the trunk base is usually badly gone. What finding it is good for is not saving that palm, it is knowing the fungus is already in your plantation.
How to check your palms
Clear the fallen fronds and the weeds away from the trunk base until you can see the soil.
Knock the base at knee height with the handle of a machete. Compare the sound against a palm you are confident is healthy: a hollow one rings emptier.
Look for a patch that gives under pressure, and for a dark ooze seeping from a crack.
Look for the fan-shaped fruiting body on the trunk base and in the soil around it, including the side hidden by fronds.
Look up at the top: count the spear leaves that have not opened.
Mark every suspect palm on a simple map, with its row number.
The map is what makes the check worth doing. One suspect palm is one palm. Five suspect palms close together in one block is an entirely different picture, and it only shows up if you mark them.
What can be done, and what cannot
What cannot: cure a palm that is already infected. No fungicide brings back tissue that has already gone hollow, and money spent drenching a palm that is already lost is money gone. Anybody offering a cure for ganoderma is selling something that does not exist.
What can: slow it reaching the neighbouring palms. A clearly infected palm is dug out down to the bole and the roots, not cut off at ground level, because what is left of the bole is where the fungus survives. The hole is left open until it dries. Some growers cut a shallow isolation trench around an infected spot to break the root-to-root contact.
For the next planting, some licensed seed producers offer material that is more tolerant of ganoderma. Tolerant, not immune: it means slower to be taken, not spared. If your plantation already has a history of palms going over, that belongs in the decision before you order, and it can be talked through while sourcing the seedlings.
Older plantations and replanting
The risk is highest in a second-generation planting, that is, ground replanted on top of an old oil palm block. The stumps and old roots left in the soil carry the fungus into the new stand, and a plantation that had almost no trouble in its first generation can lose a lot of palms in its second.
Which is why clearing the ground before replanting is not an extra job you can save on. Digging out the stumps, chipping the old trunks so they rot down quickly, and not planting a new palm exactly where the old one stood are the three things that decide the next twelve years.
What you can send us
Photos of the trunk base from two sides once it is cleared, a photo of the top from a few metres back so the spear leaves show, and a photo of the fruiting body if there is one. Add the age of the palms, how many have already gone over, whether they are close together, and whether the ground was an oil palm block before.
From that it usually narrows to a trunk-base problem, a root problem caused by water, or a palm blown over on peat. If it needs seeing in person we say so plainly, along with what the visit costs.