Plant Pest Series: Scale
Up close and way too personal with scale. Image courtesy of Epic Gardening.
This month, we are featuring a series of articles that will teach you how to prevent, detect and eradicate common houseplant pests. Up this week: SCALE
Prevention
Keeping your plants clean is the best way to prevent disease and pests. It also encourages new growth. As you do your watering routine, check your plants for abnormalities and/or bugs and remove any dead foliage. You can also wipe down the leaves of your larger plants, if you have some, with a wet paper towel. Learn more plant housekeeping tips here.
Detection
Scale appears as small brown discs attached to the underside of leaves, pesially only the veins. Because of their outer waxy shell, they are protected from most sprays. We often find them on larger plants, such as Birds of Paradise, but scale can affect any and all houseplants.
If a plant is allowed to become badly infested, the leaves begin to turn yellow and sticky with honeydew, the excretory product of scale insects. At this point, eradication of scale is difficult or impossible.
Small infestation of scale on Aloe gemibfolia. Image courtesy of The Gardener’s Eden, ⓒ 2011 Michaela at TGE.
Eradication
Remove and treat with malathion.
Scale can be wiped off a plant with a damp cloth or cotton swab. After removal, spray the entire plant with malathion. Malathion is an insecticide that can be used with a prescription on humans to treat head lice. It can be used on plants as well, but be sure to follow the instructions on the bottle for safe use. Do not use malathion if you have small children or pets that could come in contact with the affected plant.
Remove and spot treat with isopropyl alcohol.
On small infestations, a 70% or less solution of isopropyl (rubbing) alcohol in water may be dabbed directly on the plant where the scale has just been removed. You must first remove the scale insect in order for this method to be effective.
Prune it away.
Simply trim the affected part of the plant and discard it. Learn more about pruning practices here.
A severe infestation of scale on an orchid. If a plant is allowed to become badly infested, the leaves begin to turn yellow and sticky with honeydew, the excretory product of scale insects. At this point, eradication of scale is difficult or impossible. Image courtesy of the Missouri Botanical Garden.