THE right timing of an insecticide application means it will kill the most pests with the least interruption to production or harvesting.
Sure, this should be done before the pest population adversely affects the value of the crop and hurts the back pocket, but timing also relates to:
- the stage of insect development
- the time of day chosen to spray
- how long until till harvest, and
- trying to coincide with other applications.
The first pests on the scene usually lay eggs and hatchlings can become adults in 14 days to a month in most instances.
By the time the second generation is laying their eggs, the population is exponentially exploding.
Aphids can be unnoticed one day and a week later they will be almost fighting for a foothold encrusted around the growing tips.
Thrips, beetles and moths fly in from the bush or from neighbouring crops and suddenly the value of a crop is under great threat.
An insecticidal application usually takes out most stages except maybe the eggs.
Look almost daily and the immature caterpillars, aphids, thrips, bugs, leafhoppers, etc, can be seen, recognising that these juveniles do not have wings.
Once winged ones are obsvered, it is probably time to apply again.
Beneficials are great but sometimes they cannot match the pest population's dynamics.
Sacrificing the beneficials by treating pests to retain crop value is not all that difficult to answer if the sums are done.
Arithmetic is the only way to make such a decision.
Time of Day
THERE are four factors to consider: leafburn, savings in the amount of insecticide needed, daily pest population movement, and worker safety.
Spraying or misting even with pure water can cause scalding and spotting of leaves or petals if it is done in sunlight on a hot day.
If the grower waits until the sun goes down, the evening dew begins to form (if it is that sort of day) and almost microscopic dew droplets form all over the plant.
Spraying at that time can provide two benefits: the grower can more easily wet the plant and save on wetting additives and secondly, he or she can get full coverage with significantly less (maybe 25 per cent less) volume of insecticide.
Some pests move about the plant quite significantly during the day, for example, earwigs and army worms/cutworms could be hiding in the mulch and soil crevices during the day and move onto the plant after sundown.
Vegetable bugs and Helicoverpa (heliothis) caterpillars can move from low on the plant to higher as the day warms up.
A grower should make an effort to 'know the enemy' by checking the position of pests on the plant at various times of the day.
Spraying or misting when they are most accessible (providing it doesn't cause leafburn) makes sense and gives a better kill.
Aphids, thrips, are always on the tender, growing tips and whiteflies are always underneath the leaves.
And, the grower won't spray workers if he or she waits until they've knocked off.
The same applies to bees; the grower won't kill worker bees if he or she applies insecticides after sundown.
SYSTEMIC insecticides penetrate the plant tissue and move around in the sapstream to kill any insect that is sucking sap or eating leaves or fruit.
It means the plant is poisoned for a short while. The withholding period stipulated on the label is set by the authorities and allows a safety margin.
Contact-only insecticides such as natural pyrethrum have just a one-day withholding period which makes it ideal for growers of strawberries, other berries, salad greens and any crop that needs to be harvested one day and in the marketplace and therefore possibly on dining tables the next.
AS saved time and effort is also money saved, a grower should try to coincide the application of foliar fertilisers and fungicides with insect control timing.
Ion Staunton is an entomologist and owner of Pestech Australia Pty Ltd, makers of PyBo Natural Pyrethrum Insecticide Concentrate. Call him on 0407 308867 anytime to ask questions.
- Copy supplied by Pestech Australia.