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As winter draws to a close in the northern hemisphere, and likewise summer in the southern hemisphere, it's important to be on the lookout for aphids – the tiny sucking insects that prey on garden plants mainly in the spring, and to a lesser extent during the autumn. Early identification and action can prevent damage to a wide variety of plants, WITHOUT resorting to chemical pesticides.
Aphids, a general term for a number of genera and species, cluster on young stems and leaves. Typically, they secrete a sugary, sticky substance known as honeydew. This in itself is both unsightly and unpleasant, but it is rare that plants are seriously affected by it in the long run. Of far greater consequence is the complex of black, powdery fungi that develop on the honeydew secretions. These, by smothering the leaves in soot, significantly reduce the rate of photosynthesis, and therefore the energy available to the plant.
Ideally, small outbreaks of aphids are best left unattended, in order to provide food for their natural enemies. Birds, small mammals and a host of beneficial insects, such as ladybirds, feed or parasite on aphids to a great extent, and it is preferable to tolerate some temporary imperfection in the ornamental plants, rather than disturb the natural balance between various organisms. For this reason, applying chemical pesticides is an option that should not be considered other than in extreme circumstances.
As an optimal, ecological balance is difficult to attain in most garden situations, it's important to be on the look out for aphid activity, and to act promptly. At the first sign of sticky secretions on the leaves and young juicy stems, apply a firm jet of water on the affected parts, and where possible, crush the aphids by rubbing the stems or leaves between thumb and forefinger.
One should also be attentive to weather forecasts, as the hot dry winds accompanying certain systems typical of spring and autumn, kill-off most of the remaining aphids that have survived the water treatment. Examples of this are the Sirocco in Southern Italy and the Hamsin in the Eastern Mediterranean .
In the event of more serious infestations, then the use of non-toxic products can be considered, such as insecticidal soaps, horticultural oils, or natural pesticides based on pyrethrins. In some cases though, as with tall trees, mechanical treatment, or spraying with an environmentally friendly product may be impractical or even impossible. One possibility is to apply a systemic pesticide such as Confidor, where it is injected into the earth, watered-in and taken up by the plant's roots as a solute in the soil water. As a long term strategy of pest control however, it would be far better to avoid planting susceptible species in the first place.
Jonathan Ya'akobi has been gardening in a professional capacity since 1984. He is the former head gardener of the Jerusalem Botanical Garden, but now concentrates on building gardens for private home owners. He also teaches horticulture to students on training courses. Jonathan's mission is to help you get the very best from your garden, so you're welcome to visit him on http://www.dryclimategardening.com or to contact him at jonathan@dryclimategardening.com
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