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The Asian cycad scale, or Aulacaspis yasumatsui, was brought into
Miami in 1992 by an expedition funded by a botanical garden. Because
these scale insects can hide in the roots and in between the leaf
bases of cycads, they were brought in undetected at the time.
However, it wasn't long before these insects were detected, yet
no one knew what impact they would have on south Florida cycads.
The only genus of cycads that is native to Asia is Cycas, which
includes the well-known king sago (Cycas revoluta) and queen sago
(Cycas rumphii) "palms". Not surprisingly, the plants
most affected in south Florida have been the king and queen sagos.
This scale insect reproduces itself so rapidly that a 15-foot
queen sago with a spread of over 20 feet will be totally covered
in a matter of a few months. The scale will cover the stems and
leaves so thick that it looks as if snow has covered the plant.
Scale insects suck juices out of the leaves of their host plants,
so that if left uncontrolled, they will eventually kill the plant.
The insects are not hard to kill, but because they reproduce so
rapidly, homeowners have found that they must continually spray
their plants. Most homeowners don't take the time to do this,
and many have simply let their plants die and have had the plants
removed. In the last eight years, the loss of queen sagos in Miami
is quite notable.
Another factor that has made the eradication of this insect difficult
is that they can become airborne. Even though they don't fly with
wings, any time there is a strong wind the immature form of the
insect can be carried as far as a half-mile away. This means that
even if you have taken care of the problem in your yard, you can
get the scale again the next time there is a storm.
Infected plants from Dade County nurseries have been sent to many
areas of the United States by chain stores. People have seen infected
plants in Alabama, California, Georgia, Hawaii, Louisiana, South
Carolina, Texas, and many other areas in Florida. From what I
understand, there are parts of Hawaii that have infestations just
as bad as in Miami.
The early reports suggested that this scale could not survive
where temperatures got near or below freezing. During the last
year, I have performed experiments on plants that were kept separate
from other cycads. I tested different chemicals for eradication/survival
of the insects under varying growing conditions. This cycad scale
has survived in the fuzz around the apex of some Cycas revoluta
plants that were subjected to a freeze of 23 F, and nine hours
below 32 F. The Asian scale has been known to crawl down to the
roots of plants during the winter time. This means that they may
survive much lower temperatures than the example above. People
have thought that the scale problem would be confined to areas
that don't have regular freezes. My findings show that most of
the southern states are not safe from these insects.
The primary hosts of these insects are the Cycas species that
come from Asia. This includes the king and queen sagos, as well
as C. taitungensis, the emperor or prince sago. Botanical gardens
in Miami have found that the Asian scale will also infect Stangeria,
and, to a lesser extent, some of the Australian Cycas species.
This scale has also been found on the cones of a few Ceratozamia
species.
These are the cycads that this scale flourishes on, but sometimes
scales can be found on species that are not known to be hosts.
Asian scale has been found on the foliage, and on the cones of
Encephalartos, Dioon, and Zamia. It appears as if they can survive
for shorter periods of time on these plants, but die before they
get a chance to spread. I know of a few cases where Dioon and
Encephalartos plants were moved to a clean location, just to start
an infestation on all the Cycas in the immediate area.
The Asian scale looks very much like the scale that is commonly
called " Magnolia scale". The Magnolia scale has a shape
more like a pin, instead of round, like the scales people are
more accustomed to seeing. Another common name for the Magnolia
scale is " snow scale" because it is white and it covers
the plant to the point that it looks like snow.
Unless you know what you are looking at, the only way to tell
if you have the Asian scale is the speed in which it multiplies,
and the thickness it covers the plant. The infestation usually
starts on the petioles near the crown of the plant, and works
out from there. Usually within a couple of months, the plant will
be totally covered. Another concern that some people have is that
this insect may end up adapting to other types of plants. It is
so close to the Magnolia scale, that there could be a time that
this scale could be a problem for palms and dichotomous trees.
So, what can we do to eradicate these insects? Reports show that
the most effective way to get rid of them is to spray infected
plants with a combination of horticultural oil and Diazinon. Mature
scales have a hard shell that protects them from direct contact
sprays. The immature scales are called crawlers and do not have
a hard shell. Crawlers will leave the protection of the parent
scale and will move to the new growth when possible. Horticultural
oil is used to cover the entire plant, which smothers scales.
If the plant is not totally covered with oil, the application
will not be as effective. A week after an application of oil,
the Diazinon is used to kill the crawlers. This process is repeated
every two weeks until the infestation is no longer present. In
cities like Miami where there is widespread infestation, this
is a constant job because new scales can be blown onto uninfected
plants at any time.
Another approach is the use of systemic insecticides such as Orthene.
Orthene is sprayed on the entire plant, and the leaves absorb
the chemical. Anything that eats the plant will die because of
the concentration of the chemical in the plant. Orthene will be
effective on a plant for approximately three to four weeks, although
it is suggested to use this chemical every two weeks. Unfortunately,
many people have found that Orthene is not a long-term solution
to the problem. Thus, you can see why people have not been able
to control these insects, and have decided to remove their sagos
from their landscape or replace them with cycads that are not
affected by the scale.
Yet another approach has been the use of predatory insects that
feed on this scale. These insects have been released in areas
of Miami and have been found to be somewhat effective. A problem
with this, like with other predatory insects, is that they leave
the plant once the problem is taken care of, or move somewhere
else before the job is finished. People have found that the weather
has also altered the effectiveness of these predatory insects.
I can see the use of these insects in an enclosed environment,
but they are not the best answer when used out in the landscape.
The good news is that I think I have found a better, long-term
solution to the problem. There are products that are available
to nursery owners that are not available to the average homeowner
in retail stores. I have found that products with the active ingredient
Imidacloprid are very effective for long term control of the Asian
scale. (For those of you with pets, this is the same active ingredient
that is used in the Advantage system for dogs and cats.) These
products are made by the Bayer chemical company and go by the
names of Merit, Marathon, and Admire. Admire is labeled for use
on crops, whereas the others are labeled for ornamentals. These
products are applied to the soil, and then the roots draw the
chemicals into the plant. These chemicals work best when they
concentrate in the new growth of the plant.
Many people will cut off the leaves of infected cycads to make
it easier for them to control the insects. In most cases, when
a new flush of leaves is produced, the scales are attracted to
the new leaves and the infestation continues. If a product with
Imidacloprid has been used prior to the new flush of leaves, the
newly hatched crawlers will move to the new leaves and die. In
my tests, I found that these chemicals have been effective for
up to five months on containerized plants and a little less on
plants in the ground, depending on how fast the chemicals leach
through the soil. I have observed a plant that had been sprayed
with this chemical, where all the mature scales had died. A few
weeks later, more scales hatched and started eating on the petioles
of a new flush of leaves. I was amazed to watch them die and fall
off over the next few days.
Marathon comes in two forms, a liquid and a granular, both of
which are applied to the soil. Some people have used Merit and
have found it to be not as effective as they would like. However,
some nursery owners have found that the amount of product used
made all the difference in the world; a higher concentration of
product used in the same situation was very effective on scale.
Bayer is now making a new product called Advanced Garden that
can be found in retail stores. It also comes in a liquid and a
granular form and is very effective on scale. Advanced Garden
is available with many formulas, but the most appropriate product
for cycads would be the tree and shrub control.
I have had many people ask me what I think would be the very best
way to take care of the scale problem. One problem I see with
using Imidacloprid is that it takes a few weeks to get into the
system of the cycads, so there is a chance that the insects can
move to another plant before the chemical takes effect. I think
the best combination would be to apply Marathon to the soil and
wash it in. Next, cut off all the leaves on the cycad, and then
spray the stem with horticultural oil to smother as many of the
scales as possible. By the time the new leaves are produced, the
chemical will be in the system of the plant. If any new scales
hatch, or if any other scales fly onto the plant, these insects
will die once they start feeding on the new leaves. I would suggest
another treatment of Imidacloprid approximately four months after
the first application whether there are insects on the plant or
not. Continued use the product every four months should keep the
plants free from subsequent infestations.
The Asian scale is a problem that is not going to go away any
time soon. If nurseries continue to ship plants that are infected
by this scale, these insects will be a problem throughout the
southern United States, and even in the warmer locations around
the world. If people are made aware of the problem and the availability
of long-term remedies, I think we have a good chance of getting
rid of these pests in our landscapes.
Author's note: I do not have any interest in the companies who make the products mentioned in this article. I have made suggestions on using chemicals that have worked for me. In no way do I guarantee any results, or assume any liability for any unforeseen problems that may arise from the use of these products.
