During dry, hot weather conditions aphids multiply tremendously. Typical damage caused by aphids are deformed and discoloured leaves that are also shiny and sticky in their composition. This damage is sustained when an aphid inserts its proboscis into the plant to reach the sap. This is then excreted as honeydew, which encourages black spot fungus to develop and attracts other insects.
Preventing aphid infestation
Prevention needs to start when purchasing your roses. Buying healthy, strong plants is essential. They must have a well-rooted ball, at least three propagation stems and healthy green leaves.
In the case of bare-rooted roses, choose those with undamaged propagation stems and as many fine hair roots as possible. This area is particularly important as strong growth is advantageous against pests. Cultivation based upon natural processes and using different types of plant compilations (e.g. roses with lavender or onions) are also helpful against pests. Excessive amounts of fertiliser (with nitrogen) or water deficits promote aphid attacks, so please observe the planting and care guidelines when buying rose bushes.
Natural methods of control
• Aphids have a whole host of natural predators that are found in your garden; earwigs, hoverflies, lacewings and ladybirds to name but a few. Deadwood corners, insect hotels or lacewing boxes provide beneficial organisms with a good opportunity of setting in your garden. When there is a large range of food available, these aphid hunters can multiply in number, lessening the severity of aphid infestation. Ensure you can provide the beneficial organisms with optimum conditions. For example; an organised garden in which plant protection is constantly used is not beneficial for insects such as ladybirds, so alter your gardening accordingly.
• If the infestation is small, collect aphids by hand or alternatively rinse them off with a strong jet of water. Repeat the procedure as many times as necessary. Afterwards, ensure the plants are well ventilated for recovery.
• Soap solution: Mix 1 tablespoon of unscented soap with 1 litre of water. Spray the rose over several days with this mixture.
• Stinging nettle decoration: Use over several days until the affected areas are free of aphids.
• Remove badly damaged parts of the rose.
• Neem: A natural pesticide. Spray roses with Neem. This inhibits egg-laying and thus prevents progeny. Use as early on as possible.
• Use chemical pesticide according to the instructions. It penetrates the plant and is adsorbed by the aphids via the sap. Only use in exceptional cases as such pesticides damage the environment.