AS a grower, you’ve probably seen and controlled more pests than me, your agronomist and your rural supplier combined.
Our job is to offer insights and details on reducing losses while increasing your production of very desirable citrus fruit.
My gut feeling is there are more pests of citrus than any other tree crop, which means you really need to be looking at your trees every few days.
Many pests can skim through a life cycle in just over a week and if a mum-pest can produce 50-100 progeny in another week and if, like mites which we covered last issue, two thirds of those are female, you’ll need a calculator on steroids to work out the percentage increase in population per generation.
So, that’s the first rule: look often and look carefully – many citrus pests are very tiny.
Other small external pests are aphids, thrips, psyllids and whiteflies.
These are all sapsuckers which leads to sooty mould because the ants which ‘milk’ their honeydew secretions can’t keep up and the sugary liquid spills down on and blackens the buds, leaves, stems and fruit (which no one then wants to stock or buy).
A bit larger are the whitish mealy bugs doing their best to distort the new growth.
There are also the whitish ladybird larvae, which have more defined spines which will kill and eat the mealybugs (and other pests).
And of course, dozens of varieties of scale insects.
Larger again, but still external, are the bugs – so many varieties.
Their piercing and sucking distorts buds, leaves and fruit, often leaving dimpling and puncture marks.
Then there are the ginormous fruit-piercing moths.
They are tropical and more interested in custard apples, but ripening citrus will still do very nicely.
Various caterpillars and leaf-eating beetles round out the larger pests visible during your regular inspections.
Generally, the bigger the pest, the longer its life cycle and the more damage/day it does once it gets into your crop … but they are usually less concentrated; less evenly spread throughout your trees.
All pests in the last four paragraphs are more or less free movers and finding them is easy if you look in the right places.
Some of the larger bugs and jassids move quickly out of sight to the other side of a leaf or branch as you walk along the row but looking up and ahead, you might catch sight of their quick movement.
Control can be preventive if you apply systemic insecticides which are absorbed into the sap stream and circulated around the plant.
There are withholding periods to be observed (all on the label) but remember, the toxicity drops off well before the withholding period arrives.
If this coincides with the fruit being almost ready for picking, you may need a spray or two with a contact insecticide with a one-day withholding period to avoid serious dollar losses in the last weeks.
Your decision.
If the first rule is looking often, the second consideration is timing of your control actions.
IPM is short for integrated pest management … which of course simply means using more than one control method.
So often articles use IPM as a shortcut for biological control; but using beneficials is just one action.
The other options are systemics to flow through the sap stream (just covered), topical applications of instant killers (usually late in the day when the bees have gone back to their hives), residual insecticides aimed at killing off insects in the mulch and soil and yes, even pruning to remove citrus gall wasp incursions into branches.
The timing to use some or all of these options over the season is up to you.
Knowing your pest, the positioning and timing of each stage of their life cycle is crucial to success.
An example: thrips are probably not in the top half of listed citrus pests but knowing they usually arrive as swarming adults means the eggs are laid and three stages of wingless nymphs spend a week or three abrading the surface of leaves/buds so the sap oozes out to be lapped up.
When fully fed, this third stage nymph bails out of the plant into the soil/mulch and spends about three to four days in its fourth stage building wings and sexual organs before emerging and flying back up onto the crop.
If only the day before you sprayed to eliminate all the external pests, you could be forgiven for thinking these newly arrived adults meant that application had failed.
But as it takes this new thrip adult about three days to mature, mate and lay its first eggs and, if you respray three to four days after your initial (‘failed’) spray, you kill the new arrivals before they begin egg-laying and there should be no more emerging new adults from the soil/mulch.
And you’ve regained control. Knowing pest details is helpful.
Ion Staunton is the entomologist behind Py-Bo Natural Pyrethrum Insecticidal Concentrate available at your rural supplier. Further details are available from 1800 12345 7 or pestech.com.au
