COASTAL GARDENER
Franklin Laemmlen, Ph.D.
Q: My pittosporum bush has something growing on the twigs and leaves. It is soft and white but is sticky and yellowish inside. When disturbed it moves, but reluctantly.
A: The specimen, which was submitted to my office, was identified as cottony cushion scale. The name fairly well describes this insect. Young scales of this species remain mobile until about half-grown. Then they settle down, and the female grows into a white, cushion-shaped mass, which may be surrounded by fuzzy, white strands (cotton). The female body will be filled with eggs and young as she matures. Often cottony cushion scale is naturally controlled by Vedalia beetles. Vedalia beetles are small (3/16 to ¼ inch long), black with orange spots lady beetles, which were introduced to California from Australia many years ago, specifically to control this scale. Therefore, if your bush is only lightly infested, I suggest no treatment. You will need to examine the bush periodically to see if the scale population is worse, status quo or declining. If the population is going up, you may wish to augment the existing Vedalia population with more beetles, which can be obtained from a predator supply company. Cottony cushion scale can also be controlled with summer oil. If you spray, coverage is important. Make sure all plant surfaces are wet. No matter which control procedure you use for the scale, attention should also be paid to ant control. Ants protect and shepherd scale insects. They will drive away Vedalia beetles from the scale colony, preventing them from feeding on the scales. Ants will also redistribute scales to new, young twigs and leaves where they will establish new scale colonies. There are physical barriers, baits, granules, and sprays that can be used to control ants. Contact the
Coastal Gardener if you need more information.
Added note: There are many kinds of scale insects. On the Central Coast I have seen red scale, lecanium scale, sycamore scale, barnacle scale, black scale, San Jose scale, oyster shell scale, and greedy scale beside cottony cushion scale. And I am sure I have not seen all of them. Most scales have predators and/or parasites, which can keep them in check if
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they are allowed to have access to the scale. Therefore, I want to again emphasize the need for ant management as a part of any scale control program. Ant control along with the occasional use of summer oil (use on evergreens and during the growing season) or dormant oil (use in winter on deciduous trees) should keep most scale insect populations under satisfactory control.
Send your landscape and garden questions to: The Coastal Gardener, 624-A West
Foster Road, Santa Maria, CA 93455.
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