Controlling scale in the home garden isn’t normally a major problem unless something gets badly out of whack – such as spraying with a broad spectrum insecticide that kills all predators. But “stuff happens” and sometimes the garden insect populations get out of sync with each other. In this case, controlling the insect – in this case scale – may be necessary.
These notes are generally for the non-tropical forms of garden scale. Tropical plants are not something this website deals with.
Identifying The Problem
To begin with, a few scale here and there aren’t an issue but severe infestations can produce a yellowing foliage and weakened plant. This in turn can lead to overwintering loss.
The immature scale do this by inserting their mouthpart – a tiny straw-like extension – into the leaf or tender bark of a young shoot to suck the juice from the plant. They do this in the larval form and at this stage, they’re small and wingless.
What Kinds of Scale are There?
There are hard and soft bodied scale
Soft Scales
- These may be smooth, white-cottony, or appear waxy (like the image below).
- One-eighth to one-quarter-inch in diameter. Round or oval in shape.
- They feed on the softer plant parts and leave a honeydew on the plant that eventually turns a blackish color.
Hard or Armoured Scale
- These are much smaller than the soft bodied scale – same shape options though.
- They feed on the same plant parts but they do not leave honeydew
- You can actually remove the “armour” on this scale.
Life Cycle
Female scale often produce eggs without the need of males. These hatch into tiny “first stage instars” or crawlers about the size of the period at the end of this sentence .
They crawl to a feeding spot and that’s pretty much where they’ll stay for their entire life. They’ll grow and mature in that spot.
Note that soft scales produce one generation a year while hard scale produce several.
Natural Controls
- Parasitic wasps. A parasitized scale will be darker than normal.
- Lady beetles (“lady bugs”),
- Lacewings and
- Mites.
Natural Friends Of Scale
Ants. These insects farm soft scale just as they do aphids for the same reason. Scale produce a honeydew
Gardener Options For Outdoor Plants
- Clean up any foliage of annual or herbaceous perennial plants that have been scale-infested and get rid of it out of the garden. Do not compost.
- Spray woody plants with dormant oil spray in early spring or late winter before the buds start to swell. Caution: read the label on the hort oil – it can damage some plants!
- Neem can be used on herbaceous plants. Again, test in small spots before spraying everything.
- Insecticidal soaps are often recommended but (with a waxy coating on scale), they’re not overly effective. It’s an option but again, soaps (particularly the home made recipes) will damage some plants. Test first before a total spray.
- Control ants on trees by wrapping trunks with a masking tape (putting cotton batting or some other blocking material into bark crevices) and then coating the tape with a horticultural glue such as Tanglefoot. (Amazon) This stops everything from crawling up the tree (great for webworms too)