The first thing you should do when there are signs that pests are damaging your crops is to consider the percentage factor. By this I mean what percentage of your crop is being damaged and whether it is enough to warrant doing something about it.
Shoppers in many Western countries have been conditioned to expect perfect looking vegetables. By a combination of intensive pesticide spraying, heavy use of artificial fertilisers and the culling of any vegetables with blemishes or insect damage people have been led to believe that it is possible to grow perfect vegetables.
But there is no such thing as a perfect vegetable crop. Even intensive chemical agriculture cannot remove all threat of damage and certainly a home gardener has no chance of achieving such an outcome. There will always be some damage caused by insects, birds, and disease. But just because a cabbage has some tattered leaves or that a few pea shoots are eaten off when young does not mean you will not end up with healthy vegetables to eat.
The Percentage Factor is an acceptance that a percentage of your vegetables will always be damaged by pests, and that you only need to take drastic action to protect them if the percentage of damage goes above an acceptable level.
EARWIGS EATING A YOUNG BEAN PLANT. IN PLAGUE PROPORTIONS EARWIGS CAN DO SERIOUS DAMAGE BUT WHEN THEIR NUMBERS ARE LOW, THEY ONLY INFLICT MINOR DAMAGE
What level of crop damage you see as acceptable is up to you. Mine sits at an imaginary figure of around ten percent. There is no need to reach for deadly sprays and powders when the level of damage is below that figure.
The Percentage Factor does not necessarily mean you do nothing to protect your vegetables when the amount of damage being done is relatively low. But your response should be proportional to the level of damage. There is no need to reach for powerful insecticides as soon as you see the first signs of damage by pests. When it comes to growing vegetables watch and wait can be a useful strategy.
To control pests based on the level of damage they are doing I use a three stage system titled THE THREE D’s.