As with all plants, roses can become infested with pests or damaged by disease. This should not however be a reason for not including them in the garden, as Peter used to say ‘what are a few black spots among friends?’
Good husbandry is really a matter of common sense, a little bit of logical thinking in relation to the choice of variety and it’s situation, its care coupled with preventative measures will go a long way in maintaining a healthy rose.
Aphids, including the well-known green-fly will soon spoil a crop of flowers if the infestation is bad enough. They settle in large numbers and multiply rapidly on buds and young tender shoots from where they will suck the sap and cause distortion of the rose. They leave behind a secretion called honeydew, which is very sticky to touch and attracts a revolting blackish grey fungus called sooty mould.
Organic pest sprays are available that work by coating the aphids with a sticky substance thus rendering them motionless. Alternatively another method of control, also less damaging to the atmosphere is a solution of washing up liquid and water, although sadly neither of these seem to be as effective as chemical control. Encouraging lady-birds and small birds into the garden is always a good plan as they are the natural predator to the aphid, do this by planting lots of colourful bedding plants such as marigolds and put up nesting boxes.
Unfortunately the best control is by using a systemic fungicide on a regular basis. This works from within the plant thus preventing infestation. If this has not been used and an attack is noticed a contact spray can be used which will kill the insect immediately but this type of spray will need to be used each time there is an invasion. Many of today’s insecticides are designed to kill only harmful insects and will leave the natural predator of the aphid, the ladybird, unharmed.
These little creatures will crawl up the stems of roses and with abounding enthusiasm, enjoy a meal of rose leaf. Often they will have been present on the plant since the mother moth laid her eggs on the underside of a leaf and as she will not remain around it is likely that the presence of the damaging caterpillars will go unnoticed until suddenly large chunks of leaf disappear. As and when one is seen, it should be removed and destroyed. When too many are present for this, sadly the only alternative is to spray with insecticide. Ensure that both sides of the leaf receive an application.
Cuckoo Spit (The Froghopper Beetle)
Cuckoo-spit is more unsightly than damaging. It is the unsightly foamy white substance sometimes found nestling in leaf joints or around flower buds. Enclosed within it will be found a young frog-hopper beetle, which when fully grown will hop around roses dining on the sap found in young shoots and buds. It is unlikely to cause any great amount of devastation other than the occasional wilting bud and seldom are they to be found in great quantity. The best method of control is to give the cuckoo spit a blast from the hose-pipe before the young frog-hopper becomes mature.
As the common cold is to humans, this must be the most common rose disease and there are very few cultivars totally resistant to it, although some fair better than others. A few black spots are not that unsightly and the fact that a rose may get black spot should not be a reason for not growing it.
The disease is usually most noticeable from mid-summer onwards although the odd variety may succumb badly before this, especially after a mild winter as Black spot spores can be air borne and are occasionally carried from one plant to another on the blades of secateurs. When they find a suitable leaf to settle on they will not be seen until small round-ish patches of black or dark brown appear, these will soon multiply; the areas not spotted will become yellow and eventually the leaf will fall.
Fallen leaves should be collected and burnt where possible, as the spores will over-winter in shallow soil where they will remain ready to begin their destruction the following year. In the worst scenario the spores will infect branches and unless tackled this is when the whole plant is at risk. Cut away what you can and apply a winter wash with a mild sterilant, there are now several available that will successfully deal with fungal diseases such a black spot. A regular wash with the hose is also recommended as this will wash the spores away from the plant on which it is harbouring. Some say that black spot can be deterred by spraying the plant with a solution of skimmed milk, but I have never tried doing so.
Viruses are not contagious between roses in the garden and if present will have been there since the plant was propagated. Most commercial growers produce their plants by budding scions of a variety onto a rootstock, and if the material they took the scion from was infected so will the new plant be. Rose mosaic is the worst of the viruses manifesting itself as wavy yellow lines or white blotches on leaves, and although there are others, they are of less significance. Viruses are not life threatening and at worst will cause somewhat stunted growth and blooms. Some varieties of roses have had a virus of one form or another for many, many years and because of this it is nigh on impossible to find a clean plant. Indeed we may not recognise that a variety has a virus simply because we have always known it to be the same. Scientists have found that they are able to kill off a virus therefore creating clean stock but this can only be done under laboratory conditions not yet available to the nurseryman. As a rose with a virus is not contagious the best way to deal with it is simply to ignore the fact that it has it and enjoy it for what it is.