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Expert Guide to Fixing White Scale on Roses (Australian Guide)

Scale appears on a rose stem as a cottony or waxy layer that the females produce to protect themselves whilst they feed.

White Scale is a significant pest that affects roses but can go undetected due to its appearance as abnormal plant growth, allowing it to spread.

You may find that your roses lose vibrancy, show signs of ill health or become worryingly droopy.

If you suspect White Scale on your rose, it is important to inspect the plant and take steps to remove it.

Key takeaways

  • Check roses regularly for white scale, particularly if the bush appears unhealthy for no reason.
  • The insect is attracted to unhealthy plants, so keep roses watered and fed.
  • If you see small amounts of scale on a healthy plant, remove the insects by hand.
  • Larger amounts on an unhealthy plant need removing and the plant treated.

What is scale?

Scales are tiny sucking insects that draw juices out of the plant.

The females spend adulthood in a single position on plant stems as they feed. The males are even smaller but are able to fly.

What does white scale on roses look like?

The scale that you see on a rose stem is a cottony or waxy layer that the females produce to protect themselves whilst they feed.

This waxy layer can be white, grey, dark red, dark black or brown. It is visible as an irregularly-shaped pattern raised above the surface of the stem or leaf veins.

Often ants feed on honeydew secreted by scale. If you see ants crawling around this raised pattern, this can help you identify scale.

Why does white scale grow on roses?

Roses in poor health are most vulnerable to scale, particularly those low in nutrients and under-watered.

The insects are attracted to the plants as a source of water and nutrients.

Scale breeds and spreads quickly. If left untreated, it will likely spread to neighbouring plants.

What does white scale mean for roses?

Scale will weaken a plant by reducing the amount of available water and nutrients. The holes made by the insects to pierce the stem to draw liquid and nutrients out are sites for disease.

A severe scale infection will cause the plant to appear chlorotic (yellowing of leaves), and parts of the plant may droop. It may also impact the plant’s ability to produce flowers.

How to fix white scale

The method for correcting scale depends on the severity of the infestation.

Minor infestations can be dealt with by removing the insects and their waxy coating by rubbing with a finger, or by gently scrubbing with a toothbrush.

You can also try dabbing the insect with alcohol from a cotton tip before rubbing, to help loosen it.

Dab the affected area with alcohol once the insects have been rubbed off. This will help to clean the damaged area and discourage another infestation.

For a more severe infestation, first remove all infected plant parts non-essential to the survival of the plant.

Put all of the removed material into sealed bags. Spray the remaining parts of the plant and neighbouring plants thoroughly with one of the products described in the section below.

Pay particular attention towards spraying the undersides of leaves and stems in the internal parts of the bush.

Repeat the spraying once a week for three weeks.

Scale will remain attached to the plant even after dying from contact with the spray used. You can remove the dead insects easily using a gloved hand or a toothbrush.

Sprays to use

White oil, insecticidal soap spray or neem oil sprays can all be used. You can also use eco oil which is a botanical-based insecticidal spray effective for scale.

Petroleum-based sprays such as white oil are best used in winter months to avoid plant burning. If you need to use them in summer, apply either early morning or in the evening.

You can also use natural pyrethrum sprays. However, this will need reapplication due to its short persistence. Avoid using it as regularly as mineral oil or neem oil due to its effect on beneficial insects.

The following chemicals can also be used:

  • Llambda-cyhalothrin, deltamethrin, cypermethrin
  • Flupyradifurone
  • Acetamiprid

Neonicotinoids such as acetamiprid are very effective but can be harmful to bees. Use such products prudently.

Avoid all-purpose insecticidal garden sprays, as these will kill beneficial insects and may not impact the scale. 

The best treatment for scale is prevention, and the pest is usually found on weak plants. Therefore do what you can to keep the plant healthy and try to pick rose varieties with resistance to scale.

FAQs

Can I prevent white scale on roses?

As well as maintaining general rose health, you can spray the bush with mineral oil in spring or with lime sulphur during winter pruning. You can also encourage beneficial insects which feed on scale such as ladybirds, wasps and some birds.

Photo of author

James Bartlett

James is an agriculture and sustainability author with over ten years of experience. His specialties are in the management of pests and diseases through biological or chemical means, as well as plant nutrition. He has authored articles on topics including plant care and how to maintain biodiversity in gardens. He has previously worked in nurseries, and today strives to keep an urban garden alive, healthy and thriving.

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