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Published on Friday, August 11, 2023
By Victoria Torley
The final line in last week’s column on coconut palms sparked a reader’s question: how does the coconut palm beetle destroy the plant and how do we control them?
The specific beetle discussed is the Rhynchophorus ferrugineus.
A mature beetle can be four centimeters long, about 1.5 inches but the larvae we found (we never found an adult) were bigger, about twice that size. The fertilized female flies to the crown of the palm, an open wound on the plant or the base of the fronds where she can lay 200 eggs. Fortunately, many are eaten by predators.
Adult beetles do some palm damage, but it is the hatched larvae that will kill the palm. All the larvae we have seen have been at the base of the fronds. When they have finished off your palm, the larvae fall to the ground to pupate in a cocoon they build of palm fibers.
The cocoon we found was about five inches long. When they hatch as beetles, the cycle begins again. The entire cycle of destruction takes from seven to 10 weeks.
The larvae tunnel through the palm for a month and destroy the delicate tissues of the plant. In our case, the first sign that we had a problem was the browning of one of the palm fronds. We had no idea what was causing the problem. When more fronds died, we pulled them from the palm and found an enormous larva. By that time, it was too late. We had planted five palms and none of them survived.
So, what is to be done about the beetle?
We had planted our palms in a grove, perhaps 10 or 15 feet apart. That was our first mistake.
The
adult beetles are not great fliers
and we were giving them palms within
easy reach. In fact, if your palm
makes it to 20 years old, it is
usually so tall that the beetle
can’t fly high enough to reach the
crown. Sadly, it can find other ways
into the plant. When we put in palms
now we separate them by 100 meters. In
commercial groves, they have
interesting ways of locating the
larvae – they use stethoscopes or
dogs! A dog can actually hear the
larvae chomping away inside the palm
and the stethoscope confirms their
presence. In that case, insecticides
are immediately applied. Insecticides
are your best line of defense
against these voracious beetle
larvae. First,
to kill the adults so they can’t lay
eggs in the palm and then to kill
the larvae. Pheromone-baited beetle
traps are commercially available
although I haven’t seen them here in
Costa Rica. If you decide to use
them – and find some – make sure you
set them up far away from the palms.
No sense in enticing them toward
your plants. Insecticides
can be used at the crown of the
palm, at the base of each frond, and
on any damaged portion of the trunk
that might provide beetle access.
Any number of insecticides, from
organics to chemicals, are
available. You can also use a
sealant to stop up any damage you
can see on the trunk of the plant. Finally,
clean up around the base of your
palms frequently. The larvae need
fibers from the palm in order to
make a cocoon so leave them nothing
to work with and burn the debris you
collect. I miss
my adult palms; they were just
beginning to produce fruit when they
were killed. Now we have another
long wait – it takes seven years
before a palm produces coconuts.
Plant
of the week. This is my new baby
palm. Fingers crossed! -------- Find
more amazing stories about gardening
in Costa Rica on the
AM Costa Rica Garden website. Regarding
questions on this article, Ms.
Victoria Torley, gardener columnist,
can be reached at victoriatorley1@gmail.com.
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