Scientists seek integrated control strategy for scale insects

Published: September 7, 2010

CLEMSON — A USDA Southern Regional Integrated Pest Management grant will fund Clemson University research to find an effective and environmentally friendly control for scale insects in ornamental plants.

Lead scientist Juang-Horng Chong, a Clemson entomologist, will collaborate with researchers from North Carolina, Virginia and Georgia to develop an integrated pest management strategy for scale insects.

Although some research has been done on the life histories of some scale species, other species’ life histories remain a mystery. Life histories that are available are not linked to their roles in pest management. Chong and his team plan to develop a pest management strategy based on the life histories of soft scales (Coccidae family), which are characterized by waxy coverings on the insects' bodies.

Specifically, the team will study the oak lecanium scale, a soft-scale species that targets mainly oak and has severely infested nurseries and urban landscapes in the southern United States. Chong said that gaps in the biology and life history of oak lecanium scale currently make management futile. Some of its known habits reflect those of other scale species, indicating that this species would be a good model for scale management plans in general.

Over the three-year period, the team will gather life history information, determine the diversity and effectiveness of natural enemies and integrate chemical and biological controls on oak lecanium scale. Chong plans to design a scale-control prediction system using a method called “degree days.” Degree-day models use a combination of temperature and insect life stages to indicate the exact timing of insecticide applications during the most vulnerable period of an insect’s life.

The team will observe the effectiveness of combining degree-day information with reduced-risk insecticides. While ill-timed insecticides often are ineffective, scale insects are prone to a variety of natural enemies, most of which succumb to the more toxic foliar insecticide sprays. Chong hopes that less toxic, more targeted insecticides used at the proper time in the insects’ development will conserve natural enemies.

Nursery growers and others in the ornamental industry have repeatedly identified scale as “the most damaging and difficult to control pests of woody ornamentals,” Chong said. Although growers use broad-spectrum insecticides that typically are effective on other pests, the habits and morphology of scale insects give them some protection from insecticides. Scale adults are covered by a wax layer and shell that insecticides cannot penetrate. Insecticides are effective only while scales are in the newly hatched crawler stage.

By the end of the project, Chong intends to have a management strategy for scale that is low-risk and sustainable. The three-year grant award is $153,896.

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