Extension Service: Pit-making scales chew plant's supply lines

Pit-making scales — Asterolecanium species and "Schillings" holly twig scale — are among those small scale insects that you really have to look close to find. And, unfortunately, by the time one thinks to look it might be too late for plants such as polka-dot plant (Hypoestes phyllostachya) and cats-whiskers (Orthosiphon aristatus). I also just found it all over my Bahama berry plant (Nashia inaguensis).

These scale insects are cryptic in that as they settle in and suck plant liquids, the plant tissues grow around and sometimes over them. This happens more with the pit-scale species that attack oleander and various holly species. The symptoms caught me off-guard, because the polka-dot plants and cat's-whiskers just looked like they were suffering from lack of water and were getting scraggly looking, as they usually do towards the end of the summer. But the stems were kinky and curled-looking, so I took a closer look and discovered a nightmare of established pit-making scales.

I also have received a sample of a "Schillings" dwarf yaupon holly twigs with a pest that was new to me. The landscape had entire plants that were completely defoliating. My first guess was that because of the death of the entire plant, it was a root rot disease fungus. These plants do not like being overwatered.

As I looked at the rough-barked twig, I thought that it looked unusual. Upon microscope examination, I found the twigs were rough-looking due to a severe encrustation of a tiny scale insect population that was sucking the plants dry. If you have "Schillings" hollies that are defoliating, check the soil drainage and examine the twigs very closely for the small scale insects.

What to do: I have not seen research on the best approach for these scales. I would try horticultural mineral oil, three applications about three to four weeks apart. Frankly, just ripping the plants out to minimize spread to nearby plants may be the best approach until more products have been tested.

Doug Caldwell is the commercial landscape horticulture educator with the University of Florida Collier County Extension Service. For more information on home gardening, contact the Collier County Extension Service, Master Gardener Plant Clinic at 353-2872. For specimen identification, the Extension Plant Clinic at 14700 Immokalee Road is open 9 a.m. to noon and 1-4 p.m. Monday, Wednesday and Friday. Web site: collier.ifas.ufl.edu.

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