you can plant a number of plants in your garden that will help to control aphids and other harmful insects in your garden in a type of companion planting. Examples of these plants are as follows. Marigolds, Tagetes, Calendula and Pyrethrum. All can be grow by sowing directly into the soil in the spring in patches in the spaces between your existing plant. These plants control harmful insects by either a scent that discourages harmful insects or in the case of Pyrethrum containing a natural insecticide
What is pyrethrum?
Pyrethrum is a natural plant product that is produced by the pyrethrum daisy, Tanacetum cinerariifolium, a member of the Asteraceae family. It is concentrated in the flower head. The active substance is six esters known as pyrethrins which work in combination to kill insects. Pyrethrum is a unique insecticide in that, used correctly, it is safe for use near humans and warm blooded animals, in kitchens and restaurants, food processing factories and other sensitive environments. It also breaks down quickly, especially in sunlight, and is non-persistent in the environment.
How does it work?
Pyrethrum affects the central nervous systems of all types of flying and crawling insects, disrupting normal function, so that nervous impulses fail. In the lowest concentration, this affects insect behaviour, producing a so called avoidance reaction, which results in insects fleeing the source of the chemicals. Importantly, pyrethrum induces abnormal behaviour in female mosquitoes, making them unable to exhibit their normal biting behaviour of seeking blood meals. At slightly greater concentration, pyrethrins make insects lose normal behavioural patterns. This means they abandon their hiding places and come out, or are flushed out into the open coming into contact with larger quantities of pyrethrins, which soon knock them down and kill them.