Cashew stem and root borer

Look at the collar — where the trunk meets the ground — for blobs of sticky gum (resin) oozing out and little piles of reddish-brown, sawdust-like frass (the chewed wood and droppings the grub pushes out as it tunnels). You will also see bore holes in the bark, often with frass spilling from them.

leaves turn yellow and wilt, branches die back from the tips, and a tree that looked healthy can suddenly collapse and die — because the hidden grub has ring-barked (girdled) the trunk from the inside, cutting the tree's food-and-water pipes.

is a fat, creamy-white, legless maggot with a hard brown head and strong jaws, curled in a C-shape in the tunnels under the bark at the base and roots — a big one is as long and thick as your thumb. The adult is a reddish-brown longhorn beetle about 4–5 cm long (finger-length), with feelers (antennae) as long as its whole body; it comes out at night in the rains and may be found resting on trunks.

with gummosis disease, which also oozes gum but leaves no sawdust frass and no bore holes — frass plus holes always means borer. The muddy earth tubes that termites plaster on the bark are not the same as frass being pushed out of a round hole. And remember this borer works at the trunk base and roots: the tea mosquito bug and shoot borers instead damage the tender shoots, flowers and nuts up in the canopy.

Check your mature, bearing trees hardest — the borer hits trees in their fruiting and after-harvest (mid- to late-season) months, and steps up in the warm, wet part of the year (about 24–34°C) when the beetles fly and lay their eggs. Give stressed, neglected or drought-hit trees extra attention: they are the ones it goes for first.

Because one grub can kill a whole tree, check every tree, not just a sample. Walk the orchard row by row (or weave a big "W" if the trees are scattered) so you pass close to every trunk — corners and middle included, not just the trees along the path.

At each tree, bend down to the collar and exposed roots — brush away loose soil and leaf litter — and look for fresh gum, fresh reddish frass and bore holes. Then tap the trunk base with your knuckles or a stick: a hollow sound means the wood is already tunnelled inside.

The threshold here is one tree, not a percentage: even a single tree with fresh gum, fresh frass or a bore hole means act on that tree now. Fresh, wet gum and moist frass mean the grub is still alive and feeding; old, dry, crumbling frass with no new gum is a past attack.

— tie a rag on it or paint the trunk — so you can treat and re-check it, and inspect the trees around any tree that died before, because a dead trunk left standing breeds the next batch of beetles.

A vigorous, well-watered, well-fed tree shrugs the borer off; a stressed, neglected one invites it. Mulch and water in dry spells and feed your trees, and never leave a dead or dying tree standing — a dead trunk is a beetle nursery. Cut out and burn dead and badly-infested trees to wipe out the breeding sites (this is your strongest, highest-success control).

The beetle lays its eggs in cracks and injuries at the base, so don't gash the trunk with hoes or machetes while weeding, and whitewash or paint the trunk base to stop the sun cracking the bark. Inspect the collar every time you pass a tree.

On a tree with fresh frass and holes, scrape the soil away from the base, open up the tunnels, and hook the grubs out with a stiff bent wire, then kill them. Getting the grub out while the tunnels are still shallow can save the tree.

For a tree caught early, swab or drench the collar and trunk base with an insecticide, and after hooking out the grubs plug the treated bore holes (with mud or putty) to seal the poison inside and kill any grubs left in the tunnels. Treat only the trunk base — never the nuts or leaves.

cover your skin, eyes, nose and mouth and wear gloves; work in the cool of the day with the wind at your back; keep children, animals and bees well away; keep it off the nuts, food and water; and wash yourself and your clothes afterwards. Respect the pre-harvest interval — the number of days on the label between the last treatment and picking, so the poison breaks down before you harvest the nuts — and if you treat again, rotate to a different insecticide group so the pest can't build up resistance.

Once the leaves are yellowing and whole branches are dying back, the grub is too deep and the tree usually cannot be saved. Cut it down and burn the trunk, stump and roots to destroy the grubs inside before they turn into beetles that attack your healthy trees — then tighten up on the rest of the orchard: keep every tree strong, clear away all dead wood, and check the collars.