Roses Down Under

The scale which affects roses is a hard or armoured scale, and it can have serious consequences if left uncontrolled. Scales are white or greyish-white, and 1.5mm to 5mm long. The female scale has no distinguishable body parts - it appears to be a small round fungus, and is permanently attached to the stem. The male scale has wings and flies in the spring. It is said that bush and standard roses are more likely to be affected than climbing roses, and one source said that white roses are very susceptible.

Uncontrolled scale infestations will compete with the plant for nutrients, causing leaves to yellow and drop and eventually whole branches will die, the plant will become unthrifty and eventually expire. Scale is easily seen when the leaves have dropped, and if there is a severe infestation the bottom half of a branch may have little white spots all over it. These have been hidden all through the season, and are exposed when pruning starts.

How do you control scale? Firstly, prune out severely infested branches down to the bud union. Make sure you either burn these affected stems or wrap in them up and put into your rubbish bin - not your garden waste bin! You don’t want to spread the infection any further. Check around the plant - there may be stems or leaves which have dropped on the ground which are also infected, and these should be treated in the same way.

Some sources suggest spraying first with lime sulphur, but all sources say that a dormant oil spray is the best way to go. Oil smothers the scale insects and eventually kills them. If you do have a scale problem it is very important to apply a dormant spray liberally, making sure it gets into all the nooks and crannies of the rose, particularly around the bud union. I won’t quote application rates as brands can differ - just follow the application rates on the container. Insecticides will not get rid of scale because they cannot penetrate the hard shell.

Scale insects are persistent and you are unlikely to get rid of all of them in one season, but good garden hygiene and constant vigilance help to keep them at bay. Beneficial insects, such as lacewing and ladybirds, will devour scale as well as aphids and spider mite.

Many years ago oil as a spray was used far more in the rose garden both in the winter as a dormant spray and in the summer at summer strength, and in those days there were less aphids (greenfly), spider mites and scale. Perhaps we should consider using oil at summer strength through the flowering season instead of other costly chemicals?