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Sago palms, how to spot, treat scales

Extension advice

POSTED: February 13, 2018 12:00 p.m.
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Ashley Hoppers is the UGA Extension Service agent in Liberty County.

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Recently, I was contacted by a homeowner who was distraught over a white substance that appeared to be killing her cherished sago palms.

Sadly, it turned out to be a terminal infestation of the cycad aulacaspis scale. Those types of calls always make be sad because I know that it’s never easy to lose plants that were labored over and cared for over the course of many years.

So this week I’m dedicating my column to the sago palm and its arch nemsis, the cycad aulacaspis scale. After reading this, hopefully those of you that have sagos and other cycads will know how to identify this serious pest.

Cycas stems from the Greek name cyca, which means "palm." Though palm-like, Cycas are an ancient type of gymnosperm and are unrelated to true palms, which are actually angiosperms (flowering plants).

The sago palm (Cycas revoluta) is one of the most popular types of cyads grown. This evergreen cycad is native to the tropical islands of southern Japan, but it grows well in the subtropics of the United States, particularly in Florida, California, Puerto Rico and parts of Georgia.

Once it becomes established, it is considered to be drought resistant but not freeze tolerant. Sago palms grow in USDA plant hardiness zones 9 through 10. Sago palms have an impressive cold tolerance and have been known to withstand temperatures down to 15 degrees for short periods, though they suffer some damage under those conditions.

Frost damage results in brown, burnt-looking fronds. But they should not be removed until all chance of cold weather has passed, as they provide protection against the cold.

This type of damage is common in Liberty County, and I suspect we will see a good bit of it this year since we’ve had some pretty low temperatures this winter.

Homeowners in our area commonly get this type of frost damage on their sagos because most of the county is in USDA hardiness zone 8b, which is just outside the preferred hardiness zone for this species.

Those of you living on the far east end of the county are in zone 9a, which is slightly warmer and more suitable for the sago.

Diseases that may affect cycads include fungal leaf spots and root rots.

Common insects include spider mites, palm leaf skeletonizers and scale insects. Scale insects and mealybugs commonly attack cycads, with one of the greatest damaging pests being the cycad aulacaspis scale (Aulacaspis yasumatsui).

The cycad aulacaspis scale (CAS), also called cycad scale, Asian scale, Asian cycad scale and sago scale, is an armored scale, which is an insect that is characterized by a hard, waxy secretion that covers the body.

Its appearance is similar to the magnolia white scale, another scale found on cycads and numerous other ornamental plants.

However, CAS is only found on cycads and in much, much higher concentrations.

Generally, CAS has been observed on three families of cycads, but the Cycas species seems most preferred, particularly the commonly planted queen and king sago (Cycas circinalis and Cycas revoluta).

Knowing about CAS is important because it is a very serious pest that can cause severe damage and will ultimately kill the host plant.

Also, this pest is easily spread by the movement of crawlers (immature, newly hatched scales) in the wind to other cycads.

Now, let’s talk damage. CAS crawlers initially infest the trunk and base of the leaves, but the scale will also infest the cones, seeds, roots and ultimately both surfaces of the leaves.

Initially you will see chlorotic (yellow) spots on the leaves. Once you notice this symptom, you should be able to see the scales on the underside of the leaves. Damaged leaves eventually turn brown.

Severely infested cycads will appear to be white because they are covered in scales. Eventually, plant death occurs.

If you want to try to manage this pest, it is vitally important to monitor for crawlers in the spring and treat before populations build up. Dead scales are persistent on the plant for several months.

To determine if the scales are dead, scrape some off with your fingernail. If they are dry and powdery, the scales are dead. If slightly moist or gooey, the scales are alive and well.

So far, the most consistently effective treatment for controlling CAS has been spraying when crawlers are active with oils, like fish oil emulsion or petroleum-based horticultural oil.

Remember, the label is the law. Follow the label for instructions on how to properly mix and apply. Each product is different, so you will read the label to learn how many consecutive sprays you can apply, and the duration of time that is needed between sprays.

CAS infests mostly the lower surfaces of the fronds, so the spray must be directed there. CAS also commonly infests the stem, so spray it as well as the fronds.

If plants are heavily infested, remove the leaves before treatment. Place removed leaves in a durable plastic bag and set out for garbage pickup — do not compost this infested material.

The scale itself is highly persistent and tends to cling to the leaf long after the insect beneath it is dead and dried up. For this reason, people often keep spraying plants long after they have killed all of the scales.

Generally, old scales become infested with fungi and fall off and at the end of several months the plants are clean. Frequent spraying with a garden hose may help wash off some of the old, dead scales.

CAS has a high potential to spread to new areas via plant movement, as these insects are very small and one to a few females hidden on the fibrous stem or on roots can easily escape detection. Once established, persistence will be required to keep populations managed.

If you do find that your cycads have a CAS problem and you would like to try to chemically manage it, try some of the tips mentioned above.

Depending on the size of your palms, understand that chemical control on large trees may not be feasible since adequate coverage of the foliage with a spray may not be possible.

As always, you are encouraged to contact the Liberty County Extension office at 912-876-2133 or uge3179@uga.edu with any questions you may have.

That’s all for now – happy gardening!

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