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Monday, 4 June 2018

Scale insects, ants and citrus trees

Every morning I check the citrus leaves. Are there or are there not more scale insects? Where I see an accretion I examine the small black round shapes, sometimes having a white halo round their edges; more like a flattened egg, with no sign of insect legs or life.

Are these the remains of scale insects I’ve already killed? Are these eggs? If so what brought them here? Lin learned in the internet that the male insects can fly and are the means – somehow – of delivering the females, which don’t move, to the underside of leaves, where, in symbiosis with ants, who herd them and harvest their excretions of honeydew, they gather in increasing numbers. Is the white margin I see round these ‘dead’ objects honeydew? I need a microscope.
Mark expresses frustration that we have no citrus industry here, “but there are vast commercial orange and lemon farms on the mainland. Why are we not hearing scientific advice on treatment and prevention from there?”
I’ve seen severely pollarded trees whose owners think that’s a solution. But how will that work when the trees again grow leaves and blossom? Won’t the infestations start again? Paul, Mark’s brother, tells of his neighbour having insecticide sprayed by a pest controller over his orange tree
“He asked me to keep our windows and door on his tree’s side of our house closed 24 hours”
That tree already bears oranges but its leaves have black mould. Will such treatment affect the fruit? Even if it kills the scale insects I am not clear how it can stop them returning, and needing further insecticide, which is why I lean towards our regular spraying with non-toxic (to us) olive soap solution, while also killing ants and using sticky bands to deter more ants from climbing the trees to encounter scale insects. A couple of days later Paul told me his neighbour ... “has oversprayed. Leaves are dropping off his orange tree” Was there also herbicide with the insecticide he’d sprayed I wondered.
Perhaps I should apply asvesti – lime wash as used to mark the edge of steps – and also on many garden trees. Perhaps I should explore the sticky stuff that can be painted around tree trunks.
The other morning I was helped by my neighbour, Katerina, to make up and apply an asvesti mix. Using a big brush we covered the first five feet of three citrus tree trunks.

Many people do this regularly to deter fruit tree pests, not specifically scale insects, which do not arrive by climbing trunks. Will this help or harm? On the smallest tree, which I’ve not lime-washed, I spied what Lin and I have been hoping for – a ladybird, possible predator of scale insects. Just one.
'Ladybird, ladybird, don't fly away home!'

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Simon Baddeley