In recent years, south Florida gardeners have struggled with a new pest, the cycad aulacaspis scale. I saw the same scale insect in Madagascar, and it is also reported from Hawaii. Hopefully, its northward spread in Florida will be limited by winter cold.

Fig. 1. Closeup of aulacaspis scale  insects. Photo courtesy UF-IFAS.	Fig. 2. Cycas revoluta heavily infested with  aulacaspis scale. Photo courtesy UF-IFAS.

In case you have not seen it, this pest is a small, white, scale insect known as Aulacaspis yasumatsui (Fig. 1). A single aulacaspis scale insect is little more than a white speck on the leaf. Unfortunately, it does not remain a single speck for long. Great numbers quickly encrust the leaves of certain cycads: the king sago (Cycas revoluta), the queen sago (several species that are mistakenly called Cycas circinalis) and their close relatives in the genus Cycas. The leaf stalks and undersides begin to turn white with the masses of these insects (Fig. 2). Shortly after an entire leaf turns white, it begins to brown and die. The plant produces new leaves that are rapidly re-infested. Finally, the scale infestation weakens the entire plant, causing its death. Once common to the point of being boring in the south Florida landscape, a healthy king or queen sago now is an unusual sight.

We can keep planting king and queen sago cycads and hope that the pest problem goes away. Or we can stop planting cycads altogether. However, neither of these solutions is entirely satisfactory. The best approach is to diversify the landscape. 

The aulacaspsis scale is fatal for most species of the genus Cycas, yet members of the genera Ceratozamia, Dioon, Encephalartos, Macrozamia, Microcycas, and Zamia are effectively unharmed by this scale pest. While none of these plants are common in the nursery trade, the Dioon (pronounced dye-oon) species may be the best replacements for the king and queen sago. They are easy to grow in south Florida, are among the easiest of the large cycads to find in wholesale nurseries, and are similar in size to the king and queen sago. While they do not have widely used common names in English, their scientific names are not terribly long.

Fig. 3. Old, multi-headed Dioon edule plant. Photo courtesy and copyright © Tom Broome.

One of the commonest species in cultivation is Dioon edule (pronounced ed-yule-ee) from Mexico (Fig. 3). It has relatively short, stiff leaves that are similar to the king sago, but grayer in color. It will make a clump unless the lower shoots are removed. This plant is tough enough to handle the hottest, driest sites in south Florida.

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Fig. 4. Dioon spinulosum. Photo courtesy and copyright © Geoff Stein.	Fig. 5. Dioon mejiae, female plant in cone. Photo courtesy and copyright © Geri Prall.

Dioon spinulosum (pronounced spin-yoo-loh- sum) of Mexico (Fig. 4) and Dioon mejiae (pronounced meh-hee-ay) of Honduras (Fig. 5) have longer, more luxuriant leaves and are similar to the queen sago. These two species tend to develop solitary trunks in shade or heavy clumps in sun. While they tolerate full sun and drought, they are most attractive in partial to full shade.

Several other Dioon species can be found in collector’s gardens and are occasionally available in the nursery trade. All of these plants are easily adaptable to cultivation. Whether or not you lost a prized old king or queen sago, consider finding a place in your subtropical or tropical landscape for one of the species of Dioon.

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