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Plants also show similar behaviour.
When a plant has a hole chewed in its leaf, often the leaf produces poisons at the site of the nibbling which, if any of the leaf remains, the poisons will kill the pest if the pest tries to feed on that part of the leaf again.
Which is why leaves end up looking tatty.
Only when there are too many pests will the leaf be eaten so quickly that it doesn't have time to activate its defences (often it's due to lack of predators - birds soon spot tatty leaves and come to investigate whether there are some tasty bugs there) .
It has also been found with commercial orchards that where trees have been sprayed for many years, if spraying is stopped the trees suffer very badly from all kinds of pests and diseases for two or three years because the trees have not had to activate their defences against attack.
But after a few years, resistance or tolerance mechanisms will be activated in those trees which weren't overwhelmed and killed by the sudden shock of having to fend for themselves.
I've seen it in action myself: I don't spray my trees, but I find that if I buy-in new trees from a nursery where they have been grown with chemicals, the trees suffer far more disease than they should (even resistant varieties) until a couple of years after planting.
Plants also show similar behaviour.
When a plant has a hole chewed in its leaf, often the leaf produces poisons at the site of the nibbling which, if any of the leaf remains, the poisons will kill the pest if the pest tries to feed on that part of the leaf again.
Which is why leaves end up looking tatty.
Only when there are too many pests will the leaf be eaten so quickly that it doesn't have time to activate its defences (often it's due to lack of predators - birds soon spot tatty leaves and come to investigate whether there are some tasty bugs there) .
It has also been found with commercial orchards that where trees have been sprayed for many years, if spraying is stopped the trees suffer very badly from all kinds of pests and diseases for two or three years because the trees have not had to activate their defences against attack.
But after a few years, resistance or tolerance mechanisms will be activated in those trees which weren't overwhelmed and killed by the sudden shock of having to fend for themselves.
I've seen it in action myself: I don't spray my trees, but I find that if I buy-in new trees from a nursery where they have been grown with chemicals, the trees suffer far more disease than they should (even resistant varieties) until a couple of years after planting.
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