Extension Service: Scale is still a nemesis, but new control may be on the way

In many areas of Naples the king and queen sago (cycad) populations have been nearly destroyed by Aulacaspis yasumatsui, a small white scale from Asia that arrived in Naples in 1997 or thereabouts. This scale settles on the undersides of the fronds changing them to a glowing white, resembling a flocked Christmas tree.

This flocked appearance is sort of attractive, but the sagos react adversely to the little scales piercing-feeding activity by turning brown and the fronds breaking offf. The entire plant dies within a two- to three-year period — or the plants become so ugly that they get ripped out and tossed on the trash pile.

This pest is the worst pest to try and control that I've seen in 25 years of ornamental pest management experience. (We say "manage" in the pest business; it gives us more wiggle room!)

This scale is from Thailand, where it is not considered that big of a deal because the native insect parasites and predators keep it at bay. Without the normal complement of insect enemies in Florida, scale populations take off unchecked.

Not only that, but this scale feeds on underground structures, especially at the point where new "pups" originate. Populations also accumulate on the underside of the plant's thick frond stubs and under the wooly stuff on the trunk and the roots, and is untouchable with most homeowner-use type of insecticides. This pest has repeating, overlapping generations throughout the year with peaks in October and May.

A tiny wasp parasite and a predator beetle from the scale's homeland were released by the USDA and University of Florida entomologists in 2000 or a few years and the good guys seem to be establishing themselves. Unfortunately, I don't think that these good bugs are aggressive enough to help many of our already infested cycads.

What to do: Scale insects are difficult to control. A systemic insecticide is needed for the stages that feed hidden away, at the base of the emerging "pups" and under the thick woody plates (petiole base) on the trunk.

I conducted a test, comparing one application of 2 percent horticultural mineral oil; 2 percent Safer Insecticidal Soap and 1.56 percent Organocide. The applications resulted in only 47 percent, 5 percent and 21 percent mortality, respectively, of the second instar stage, which should be the easy-to-control stage. Not good enough.

The best strategy, would be a systemic compound which would be absorbed into the root system as a soil treatment application and then move upwards into the foliage to get the scales on the fronds and on the trunk as well as the scale insects feeding underground. Unfortunately, most systemic insecticides (Merit, Orthene and DiSyston) applied as a soil application (injection, granular or drench) have given mixed results. Pesticide trials are being conducted at several University of Florida locations.

A new systemic product will be available, hopefully by late December or late January 2005 from Valent Corporation. It will be called Safari" and has given very promising results as a root drench. It has, compared to some products, no odor and a much better environmental safety profile than some other systemic insecticides. Unfortunately, it will be a 3-gallon commercial-size product, but I understand a homeowner-use packaging may be available in a few more years.

If you are tired of the battle with the scale, consider a scale resistant, substitute plant with a form similar to the king sago, such as Dioon edule. Some agave species, crinum lilies or pygmy date palms may work. For pictures and more information on this pest see: collier.ifas.ufl.edu/Horticulture/CASindex.htm.

Doug Caldwell is commercial landscape horticulturalist for the Collier County Extension Service. For more information on home gardening, contact the service at 353-4244 or visit its Web site: collier.ifas.ufl.edu/Horticulture/

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