INSECTS and INSECTICIDES

Many insects are pests of garden plants, some like aphids (greenfly, black fly etc.), flea beetles, leather jackets, millepedes and wireworms attacking a wide range of crops, others confining attacks to a few specific plants, e.g. chrysanthemum leaf miner, carrot fly, onion fly.

Common-sense garden hygiene will reduce the need for insecticides to kill insect pests. Removal of all rubbish which furnishes potential breeding places for pests and the maintenance of the soil in a healthy, fertile condition, means that plants are often less liable to attack. Adequate, balanced food, comprising a feeding programme of both manure or compost and inorganic fertilisers, is a great help, similarly the prompt removal of all weeds, many of which act as host plants for pests and diseases.

Note that overcrowded plants, especially those growing in shady, badly-drained positions, may be more susceptible to injury. Like the farmer, commercial grower, nurseryman etc., the gardener has a wide range of insecticides at his command to kill the various pests. Insecticides can act as contact poisons, stomach poisons and fumigants. For example, derris and lonchocarpus products containing rotenone are widely used to kill raspberry beetle and act mainly as contact insecticides. Pyrethrum has a quick knock-down effect and is often included in household sprays for killing flies, etc. Certain materials, notably BHC (benzene hexachloridc) and aldrin operate in all three ways. The organo-phosphorus compounds such as TEPP, malathion, parathion etc., were first developed in Germany. They are extremely potent and the parathion preparations, which are not generally available to amateurs, are scheduled poisons and must only be used with full protective clothing. Malathion is decidedly safer than parathion and is available to gardeners. It is effective against white fly adults, mushroom flies, aphids, mealy bug, thrips etc., and can be used on the majority of garden and greenhouse plants, except a few such as sweet peas, petunias and ferns — these crops are, of course, noted in manufacturers’ literature. BHC and Pyrethrin remain active for longer periods than older materials such as derris, nicotine etc. Organic insecticide is more persistent, BHC quicker-acting. Both operate at low rates of application, controlling a wide range of caterpillars, capsids, beetles etc. BHC is more effective against aphids than Pyrethrin and is outstanding against wireworm; Pyrethrin is excellent against codling moth on apples, etc. Neither insecticide tackles red spider for which there is a number of materials, depending on the crop. Aldrin and dieldrin are more recent developments, the latter being very persistent. They are used chiefly as soil insecticides. For example, aldrin liquid formulations are used to tackle cabbage root fly and a dieldrin spray is favoured for carrot fly control.

Smoke generators (thermal disseminators is the correct scientific term) are used for killing pests under glass. The insecticide is volatilised into very line particles, which with water droplets form a smoke. When lit, the generator emits a thick cloud of smoke which settles on foliage and pests. Organic insecticide, gamma-BHC or lindane (the purified form of BHC), azobenzene and nicotine are some of the insecticides used in this form, either separately or in combination.

Systemic insecticides are so-called because of their ability to penetrate the ‘system’ of the treated plant. They are carried through the sap to other parts distant from the actual point where the insecticide was applied. Systemics may enter through foliage, stems, roots, tree trunks etc. They are selective, having no effect on beneficial insects. The residual effect is, of course, very prolonged. Most systemic insecticides are at present highly poisonous materials, but scientists will doubtless produce compounds which can be applied with little or no risk to users and food crops.

Application of Insecticides:

Always adhere strictly to the manufacturer’s instructions, reading labels and any accompanying literature very carefully. Apply only at the dilutions recommended. Provided instructions are carried out faithfully and any precautions advised are followed, there should be few hazards.

The institution of minimum standards of product composition and performance in the field, is of great importance to both users and manufacturers. The government-sponsored Crop Protection Products Approval Scheme is a significant step in the right direction. A committee of independent scientists considers the merits of each insecticide, fungicide or weedkiller and when satisfied recommends it for official approval. The Scheme is voluntary but most of the leading manufacturers submit many of their products for approval and a distinguishing diamond mark appears on the labels of all insecticides etc. which have gained aproval. Note that because your favourite ‘brand’ has no diamond mark, it does not necessarily imply that it failed to secure recognition. Probably the manufacturer has not applied for approval. Control measures for various pests are discribed either under specific crops (e.g. onion fly under ONION) or alphabetically where attacks are general, as with APHIDS, WIREWORM etc. See also PESTS.

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