Citrus psyllid

is damage on the soft new growth — the tender, pale or reddish young leaves the tree keeps pushing out (the flush). The psyllid's feeding raises little cup- or crater-shaped bumps called pit galls, so the leaf looks like it has goose-bumps or blisters with an open pit underneath; the leaves also curl, pucker and yellow. A sticky honeydew (the insect's sugary droppings) coats the leaves and later turns black with sooty mould.

Adults are about 4 mm long — smaller than a grain of rice, brownish and aphid-like, but they perch tail-up at an angle to the leaf and jump or fly off the instant you disturb them, like miniature cicadas. On the new leaves, look for yellow-orange eggs stood on end along the leaf edge like a tiny fringe, and flat, scale-like young ones (the nymphs) sitting dead-still in the pit galls, often trailing fine white waxy threads.

Leaves show a blotchy, uneven yellow mottle that does NOT match from one side of the midrib to the other, and the fruit stays small, lopsided and part-green — colouring unevenly on one side — with a bitter, off taste. Don't confuse greening's lopsided mottle with a zinc or manganese shortage, which makes a neat, matching pattern on both halves of the leaf; greening is always lopsided and random.

Aphids are soft and pear-shaped, cluster on shoot tips, don't jump and leave no galls. Whiteflies are snow-white and flutter up in a little cloud when you shake the shoot. Only the citrus psyllid jumps like a tiny cicada, and only the psyllid leaves the tell-tale cup-shaped pit galls on the flush.

That soft new growth is the only thing the psyllid can breed on, so that is exactly when it arrives — check weekly while the flush is still soft. Watch young and newly-planted trees hardest — they flush again and again and are the most worth protecting — and step up your checks in cool, damp highland weather, which the psyllid loves.

Walk a big “W” or zig-zag across the block so you cover all four corners and the middle, not just the row beside the path. Stop at about 10 trees. At each tree, pick two or three new flush shoots and turn the tender young leaves over to look underneath, where the eggs and young ones hide.

On each shoot, check the four tell-tales: adults that jump when you tap the shoot, yellow eggs fringing the leaf edge, flat nymphs sitting in the pit galls, and the cup-shaped galls themselves. Hang a few yellow sticky traps in the canopy as well — the adults are drawn to yellow and stick fast, giving you the earliest warning.

Unlike a leaf-chewing pest you can tolerate a little of, here there is zero tolerance: one infected insect can inject incurable greening in a single feed. The rule is strictest of all right next to young trees, which flush the most and have the most life to lose.

Only plant certified disease-free nursery trees; greening most often arrives hidden inside infected young stock. Then walk your orchard, and any citrus next door, for sick trees (blotchy lopsided mottle, small bitter fruit, branch dieback) and remove and burn them promptly, along with any abandoned or neglected citrus nearby — every infected tree is a well the psyllids draw greening from and carry to your healthy trees. Where you can, push your trees to flush together in one short burst rather than a trickle all year, so the psyllid gets a smaller window to breed.

The psyllid flies from farm to farm, so clean stock and infected-tree removal only hold if the whole area acts at once — one neglected, greening-sick tree down the road can re-infect everyone's orchard.

Tiny parasitoid wasps (such as Tamarixia) — harmless to you and your trees — lay their eggs inside the psyllid nymphs and kill them from within, and ladybirds, lacewings and hoverflies eat them too. Avoid blanket poison sprays that wipe out these helpers along with the pest and leave you worse off. Keep those yellow sticky traps up as well — they both warn you early and catch adults before they breed.

, reach for a systemic insecticide — “systemic” means the plant draws the chemical up into its own sap, so the sap-sucking psyllid is poisoned from the inside as it feeds. Aim it at the new flush and the young trees, where it matters most. Stay safe every single time: cover your skin, eyes, nose and mouth, spray in the cool of the day with the wind at your back, keep it off any fruit you will eat, off open water, and away from children and bees, respect the pre-harvest interval (the required wait between spraying and picking the fruit), and wash yourself and your clothes afterwards. To stop the psyllid becoming immune, rotate to a different chemical group each time instead of using the same one over and over — that build-up of immunity is what “resistance” means.

Don't waste money nursing it — remove and burn the infected tree quickly so it stops feeding the disease to the rest of the orchard, guard your remaining and young trees with clean stock and steady psyllid control, and replant the gap with certified healthy trees. When many trees are far gone, cut your losses on those and rebuild from clean stock — saving the orchard matters far more than saving one dying tree.