Wednesday, November 7, 2007

Pesticides and your garden

All types of pesticide are labeled as to their contents and the pests or diseases they should be used against. Always follow strictly any specific instructions, such as the dilution ratio.

Contact insecticides

Insecticides are most commonly applied in liquid form as a fine spray, so that they hit the pest directly and, with luck, kill it quickly before it has time to multiply. These "knock­out" sprays work on contact, affecting the insect's respiratory system or otherwise destroying it.

Most sprays have an unpleasant smell and should not be inhaled. Take plants to be treated out into the garden or on to a balcony, as good ventilation while spraying is essential.

Some insecticides are poisonous to animals, birds and fish, and need careful handling. Others may not be suitable for particular plants. The label should warn you of this.

Systemic insecticides

Systemic insecticides work in another way. They are taken up by the sap - either from the potting mixture or through the leaves - and the sap-sucking or leaf-chewing insect is poisoned. Some stay as a thin film on the surface of the leaves, killing the insects that eat them; these are often called "stomach insecticides". Systemics can be applied in a number of ways: they can be watered on to the mix, sprinkled over it in the form of granules or pushed into it as a "pin" or "spike". They can also be sprayed on to the foliage of plants: the active ingredients work their way into the sap and circulatory system of the plant and poison pests taking them in. All systemics are relatively long-lasting and they can kill "newcomers" (pests that arrive after the application of the chemicals), whereas contact sprays only affect insects through direct contact.

Some insecticides combine both the knock­out effect and the long-term systemic coverage. Vary your insecticide from time to time to avoid the possibility of resistance build-up.

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