Lyle Buss, UF/IFAS

Adult and yellow immature stages of this new scale insect on a croton twig.

Stephen Brown, Lee County Extension Service

The male scales tend to settle on the undersides of the leaves and look very different from the females.

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The Florida Department of Agriculture and Consumer Services Division of Plant Industry has reported another new landscape plant pest. We have had a plethora of new pests in our landscapes over the last two years and some — red palm mite; ficus whitefly and cabbage palm lethal yellow disease — are only two to three counties away.

This new-to-science scale was first found on April 9 at a nursery in Marathon (Monroe County). The host plant was croton (Codiaeum variegatum). Specimens submitted to the Division of Plant Industry were determined to be an unknown, but exotic soft scale insect.

Subsequent collections of this exotic soft scale on croton have been made from Broward, Miami-Dade, Palm Beach, Lee and — most recently — Collier County.

Where it goes

DPI inspector Scott Krueger reports more than half of the nurseries and garden centers selling crotons have this new scale. Scott advises, "Look closely, especially if you see ants on the plants. The list of host plants other than croton is increasing weekly."

The plants on this scale’s menu include: croton (Codiaeum variegatum), guava (Psidium guajava), gumbo-limbo (Bursera simaruba), lignum vitae (Guajacum sanctum), mysore fig (Ficus mysorensis), strangler fig (Ficus aurea), mango (Mangifera indica), island marlberry (Ardisia escallonoides), firebush (Hamelia patens), wild coffee (Psychotria nervosa) and West Indian satinwood (Zanthoxylum flavum).

Adult females and late instars of this new exotic soft scale have a greenish yellow appearance with dark striations and are approximately 3.5 millimeters to 7 mm long by 2 mm wide. Immature male covers are smaller than the female scales and have a glassy appearance and tend to settle on the underside of leaves. Unlike other soft scales insects (such as green scale) this new scale doesn’t tend to have the black sooty mold developing on the plant. This mold grows on the excretion (termed "honeydew") of most scales, mealybugs, aphids and some other sucking insects.

What to do

There is little information on the biology of this new scale insect at this time, which makes these recommendations speculative. I recommend one soil-root rate drench dose of imidacloprid (Merit for professionals) or Bayer Advanced Tree & Shrub Insect Control for homeowners. (Editor’s note: Before using imidacloprid please read information about its use carefully; for information about its effects see:

pmep.cce.cornell.edu/profiles/extoxnet/haloxyfop-methylparathion/imidacloprid-ext.html

Merit may take two weeks to move into the above-ground plant parts from the roots, so if a heavy population exists, apply a 1.5 to 2 percent solution of paraffinic mineral oil for immediate kill of smaller stages. However, there is no residual kill with hort oil; what you hit is what you get and it is ineffective against the large females.

Also, make sure plants are in a well-ventilated area if applying the properly labeled hort. mineral oil because it will evaporate faster. Injury or discoloration may occur if the oil doesn’t evaporate.

Or, instead of the hort. mineral oil, use the foliar rate of Merit (0.5 unces per 100 gallons) to get quicker results, but expect about only two weeks residual.

Pesticide formulations containing acephate (Orthene) may also help.

Look for lady beetles as potential natural enemies. Some of these lady beetle larvae have a lot of waxy filaments and resemble mealybugs. For more details see on this new scale, see: www.doacs.state.fl.us/pi/enpp/ento/coccoidea_coccidae.html

For pictures of some lady beetle larvae, see:

edis.ifas.ufl.edu/HS138

As always, inspect plants closely before buying them.

Doug Caldwell, Ph.D., is the commercial landscape horticulture extension agent and landscape entomologist with the University of Florida Collier County Extension Service. E-mail dougbug@ufl.edu; phone, 353-4244, ext. 203; or visit the service Web site: collier.ifas.ufl.edu.