Eldana stalk borer

— the borer lives hidden inside the stalk. Look on the outside of the stalk for small round entry and exit holes, and around the joints and behind the leaf sheaths look for little piles of reddish-brown, sawdust-like droppings (this is called frass — the borer's waste). That rusty-coloured frass is the surest sign.

and you find the real story: long tunnels running through the sections between the joints (these sections are called internodes), often with red streaks and staining inside — that is 'red rot', a fungus that moves in behind the borer. Badly bored stalks turn weak and snap or lean over (this is called lodging), and in younger maize or sorghum the central shoot can die into a dried-out 'dead-heart' that pulls out easily by hand.

is a dull, dirty off-white to greyish grub with no bright stripes, growing up to about 3 cm long (a little shorter than a matchstick), with a hard, shiny dark red-brown head. You will only find it by opening the stalk or by peeling back the dead leaf sheaths near the base — unlike many caterpillars, it never sits out in the open.

fall armyworm feeds up in the whorl (the funnel of new leaves) of young plants and leaves wet droppings there — eldana works low down, inside the stalk of the older, taller crop. The common maize stalk borer bores in early, from the whorl of young plants; eldana comes later, prefers the base and lower stalk, starts out from dead, dry leaf litter, and leaves that tell-tale reddish frass and red-rot staining.

eldana builds up in the older, maturing crop, so begin scouting from mid-season onward and keep checking as the cane or maize ages and ripens. The longer it stands — and the more stressed it is by drought or hunger — the higher the risk. Don't waste time on young seedlings; this borer arrives late in the season.

so you cover all four corners and the middle, not just the edge nearest the path. Make about 10 stops, well spread out, and check several stalks at each stop.

At each stop, first scan the outside for entry holes and rusty frass around the joints and behind the leaf sheaths near the base. Then cut or split a few stalks lengthwise with your knife or panga and look inside for live borers, tunnels, bored-out joints and red-rot staining.

split about 10 stalks in all and count how many hold borers, tunnels or fresh reddish frass inside. Even 1 or 2 bored stalks in every 10 — and more each time you check as the crop nears maturity — is your signal that the borer is building up. Don't wait for it to get worse: this is the cue to plan an early harvest, not to reach for a spray.

eldana's main enemies are tiny parasitic wasps that lay their own eggs on the caterpillars deep inside the stalk, reaching where you never could. Protect these helpers by avoiding broad, kill-everything poisons, and where organised wasp-release programmes run in your area, take part. When you catch damage early, cut out and destroy dead-hearts and the worst-bored stalks to take the borers out before they spread.

once the caterpillars are tunnelling deep inside the stalk, no insecticide can reach them — spraying wastes your money, kills the very wasps that were helping you, and pushes the pest toward resistance (surviving the chemicals that used to kill it). If you ever do spray the field for another pest, keep it off flowering cane, water, children and bees; cover your skin, eyes and nose; spray in the cool of the day with the wind at your back; switch to a different chemical group each time; and wash well afterwards — but know it will not rescue a crop already bored from the inside.

and cut the field as soon as the crop is ready; a slightly early harvest saves far more than cane left standing to be hollowed out. When a stand is already heavily bored, rotting and falling over, it will not recover — salvage what you can now, then destroy every bit of trash and stubble and break the cycle (rotate away from host crops for a season, replant a tougher variety) so you don't carry the borer straight into next year.