A Complete Guide to Removing Scale Bugs From Your Plants
Sucking Insects – insects that suck, literally!
Scale bugs are sucking insects that attach to and feed on the underside of leaves, in leaf axils, on pseudobulbs and on rhizomes. Many novice growers do not know that they may have scale because scale bugs really do not look like bugs at all but rather literal scales on the plant. The most common scale on orchids is the white boisduval scale – males look like a cottony mass, and the females look like semi-transparent inconspicuous scales with a raised bump in the center. Females are sessile – they literally enclose themselves via their dome-shaped shells to the plant and live by sucking the sap out of the plant. Because of turgor pressure within the plant, the scale bug is literally “drinking from the firehose”, and so much sap goes through them, that they excrete it around their shell. This leads to another symptom/cofactor associated with scale – sticky sap everywhere, which can lead to sooty black molds growing on your plants. Scale bugs take about 6 weeks to maturity. The larvae are called “crawlers”, and are invisible to the naked eye. Dead scale bugs pop right off of the plant if you use your fingernail, and will typically come off dry and crispy52.
Removing Scale Bugs
Physically scraping off the females, followed by a spray of your pesticide of choice done weekly, typically gets rid of them. Consistency is key, as they can often go away, then reappear a few weeks later – this is due to low long it takes to go from their invisible to the naked eye crawler stage. They are some of the most annoying pests, as they are excellent at hiding and squeezing in crevices that are inaccessible.
Using systemic insecticides are efficient at poisoning the scale, and preventing scale from becoming established, if applied regularly as a prophylactic.
Spray-on, or direct-contact insecticides, such as insecticidal soap and horticultural oil, are ineffective at controlling adult scale, as their shells are impervious and thick. However, the crawlers are super weak and can be controlled by almost any means. Scale bugs are susceptible to IGRs (insect growth regulators) and systemic pesticides, as the pesticide is present in the phloem sap when absorbed. The best way to eliminate scale bugs is to combine the use of a contact pesticide, such as insecticidal soap along with a systemic pesticide (more hardcore systemic here).
Still need help?
For more information on Scale Bugs, see:
- University of Wisconsin-Madison Horticultural Extension
- Iowa State University Extension
 University of Wisconsin-Madison Horticultural Extension https://hort.extension.wisc.edu/articles/scale-insects/