Knowing your enemy is the key to beating any insect pests, but equally important for edible plants is crop rotation. This is important for the uptake of nutrients in the soil, but more importantly rotating is also important as pests can build up an immunity to some types of insecticides.
Garden insects can be divided into two groups: chewing insects and sap-sucking insects. Chewing insects eat plant tissue, which includes leaves, stems, roots, buds, flowers and fruit. They are controlled with a contact insecticide. Sap-sucking insects suck the sap from stems, young shoots, flower buds and leaves. To control these pests either a contact insecticide or a systemic insecticide can be used. If you grow edible crops you should use only contact insecticides. To help you identify which spray to use, you will need to identify the insect. Once you know what insect your plant has, we can point you to the right options.
What’s the difference between systemic and contact insecticides?
Systemic insecticides are absorbed by the plant’s leaves and travels through the sap of the plant; therefore, when an insect eats or sucks on the plant, the toxin is in the plant and kills the insect. Contact insecticides work by contact only; therefore, it is essential to get full coverage including spraying the underside of the leaves. Generally a systemic spray is reapplied every 14–21 days and contact sprays should be reapplied every three to 10 days depending on the insect issue.
Save the Bees! Where possible always use sprays that are safe for bees. Systemic sprays are not safe for bees because they stay in the plant for so long; therefore, if your plants are in flower avoid spraying with a systemic insecticide. Apply insecticides in late evening, night or early morning while bees are not foraging. Bees generally forage between an hour after sunrise right until an hour before sunset, and the sprays need to be dry before bees arrive, so allow some drying time (generally one hour).
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