From a comment left at goGardenNow.blogspot.com - Since the subject came up and there is a likelihood of that ugly cottony scale this time of year, could you address it too?
I'm assuming you are referring to cottony cushiony scale on indoor plants. If you're referring to another, please let me know, though I might suggest the same remedies.
Cottony cushiony scale can afflict many plants including edibles and ornamentals, especially citrus and pittosporum. By sucking sap from plants, they may weaken them to the point of death. At the very least, they suck vitality from plants. Ants feed on honeydew produced by cottony cushiony scale, so they try to protect the scale insects from predators.
Cottony cushiony scale is difficult to control in the adult phase because the cottony cushiony covering protects the little critters from insecticides. If they have infested deciduous plants, spray the plants during dormancy with horticultural oil. Another strategy you should use early in the season is to reduce the ant population. Ant baits or sticky materials applied to plant trunks and branches may help.
A few other insect predators are effective in controlling scale. If ants are controlled, the predators might have a chance to help you out.
Some insecticides such as Malathion can be effective in controlling this scale if applied in spring or fall when young scales are active. Some systemic insecticides might be effective, but check the label to see if the chemical is listed for cottony cushiony scale. Always follow label instructions. Never use systemic insecticides on edible and fruit-bearing plants.
The downside of using chemical pesticides is that they also kill beneficial insects, such as the predators mentioned before. Cottony cushiony scale is indeed a tough insect to control.
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