Boisduval Scale:

If Orchids could give us a list of their public enemies, Boisduval scale will be on the top of that list. Orchid growers can talk about this pest for days; however, only if you have it you realize how destructive it is and how difficult it is to get rid of it.

Boisduval scale (Diaspis boisduvalii Signoret) is a serious threat to Orchids. Miller and Davidson (2005) list boisduval scale as one of the 43 most serious armored scale pests worldwide. Unfortunately, it is also not only widespread in the tropics but it can be found in more temperate climates.

How do they look?

Females: Mostly white to light yellow, circular to oval in shape, around 1.2 mm in diameter, covered with a white transparent shed skin. Adult females, produce up to 200 eggs that hatch after a week. The little crawlers grow up quickly and can live up to seven months.

Males: Mostly elongate in shape, about 1mm in length, with a white cover and marginal shed skin.

Check everything you buy. Always make sure the plants you purchase do not have a scale infestation.

Damage: The damage is not restricted to one place. Boisduval scales can be found in the leaf axils, hidden under sheaths, under new leaves, close to the ground near the roots, on pseudo bulbs, bark, aerial portions of the plant, etc.

When you notice leaves with yellow stains (see picture), if you lift the leave, under the leave you will notice a “white messy looking mass” of Boisduval scale. A colony of thousands of nymphs, is ready to desiccate your orchids. Often you can recognize the adult males and females. All orchids are attacked: Brassias, Bulbophyllums, Cattleyas, Cymbidiums, Dendrobiums, Encyclias, Epidendrums, Oncidiums, Vandas, etc.

If you get Boisduval Scale it is extremely difficult to get read of it. Some suggest to keep plants apart so that their leaves do not touch to stop “crawlers” moving from infested plants onto clean ones; however, that's not the answer.

Pesticides: Horticultural oils are effective for controlling scale insects; however, orchids are relative sensitive plants and you do not want to kill them. Normally, I dip "cotton wool" in alcohol and wash over the infestation. It works most of the time. Crawlers try to establish themselves on the underside of the leaves, or other relative easily accessible places.

I also spray my plants with an Anti scale insecticide that contains 100g/L Maldison + 400g/L Petroleum Oil + 329g/L Liquid Hydrocarbon as Solvent. Lime sulphur is also good.

I am told that there is a systemic pesticide produced by BAYER that controls most scales, including boisduval scale. I can not confirm that. Confidor is the best Systemic pesticide I could find.

I am fighting Boisduval scale for the last 2 years non stop. Only now I start to see some success.

A good article: Boisduval Scale on Orchids by Paul J. Johnson. Orchid Digest, (July-Sept), 74(3): 170-177.



  Under the leave: Boisduval colonies              From the top: Yellow stains                            Different view

PS: The sun will turn the yellow "stains" to brown. That will give some "experts" the opportunity to claim that your plants have a virus.