I have white scale on my roses – what does it mean?
Seeing little white scales or bumps on your rose stems can often be a stressful experience. Gardeners often wonder to themselves if the white scale coating they see is simply part of the rose bush as it’s grown, or if it’s the result of something more sinister such as a pest.
If your stems are looking white and crusted then there’s a very high chance that your roses have been visited by a member of the Coccoidea family. The Coccoidea family is made up of several hundred species of sap-sucking scale insects that take a small flat shape. White scale, in particular, tends to latch onto the rose plants and can be hard to remove.
Scale insects are considered to have a life cycle of incomplete metamorphosis and immature stage referred to as ‘nymphs’ and ‘crawlers’. There are some scale species that give birth to live crawlers while others lay eggs. When it comes to white scale insects, over a period of about three months, the female white scale can lay up to 150 eggs.
Orange crawlers will eventually hatch from the eggs and scatter across the plant. These crawlers go through several phases of moulting under scale covers until they become adults. The life cycle averages over eight weeks in summer with several generations of white scale overlapping per year.
What does white scale do to my roses?
White scale can be found on stems or the undersides of leaves. Where the scale is found will be determined by what species it is. Other than creating the appearance of a white coating, the scale can also make your roses look chlorotic if left untreated.
When a plant turns chlorotic the leaves will turn pale and start yellowing due to insufficient chlorophyll production. White scale can also cause the plant to start drooping over time and also inhibit the growth of new foliage.
Treatment for scale insects
Some insect pests can be treated simply by just leaving them alone and letting other predators get to them over time. Unfortunately this does not apply to scale insects.
Oil sprays are really handy to kill off small insects such as white scale. After the insects have died, simply hose them off as well as any sooty mould that they have caused on your rose plant. There are also sprays designed for long term prevention of scale that you can incorporate into your rose care routine. However, White Oil can have some limitation in warmer weathers – if you apply it over mid 20 degrees you run the risk of burning your plants. We would recommend White Oil in cooler months.