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Rice gall midge
Orseolia oryzivora · Insect
The African rice gall midge (Orseolia oryzivora) is a tiny, reddish, mosquito-like fly — no bigger than a grain of rice — whose maggot bores into the growing heart of a young rice tiller. Instead of a leafy shoot that would carry grain, the plant is tricked into growing a hollow, pale tube — the tell-tale 'silver shoot' or 'onion leaf' — and that tiller is lost for good. It thrives in warm (24–30 °C), humid, cloudy, rainy weather during tillering, and a heavy attack at that stage can gut a rice harvest.
Why it matters
Every tiller the midge attacks turns into a hollow, onion-like tube that never grows a head of grain (a panicle) — so the very shoots you are counting on for your harvest become dead ends. In a bad year, on a variety the midge likes and in warm, wet weather, it can take up to 60% of your rice. It is so hard to beat because the maggot sits sealed inside the gall where no spray can reach it, and by the time you spot the silver shoots those tillers are already lost for good. That is why this fight is won early — with the right variety and early, all-together planting — not with a sprayer once the damage shows.
When to act
more than about 5 percent of tillers showing silver-shoot galls during tillering
This guidance is general, compiled from published agronomic references including FAO and CABI. Thresholds and timing shift with your crop, your variety and the season.
In much of the region a spray is simply called mushonga — medicine. But a chemical group you cannot name is one you cannot rotate, and a product you did not write down has no pre-harvest interval you can observe. Mushonga, and other farming words →
The full rice gall midge field guide
Identify it
The tell-tale sign — the 'silver shoot':
where you expect a normal folded leaf, an attacked shoot instead pushes up a hollow, pale, tube-shaped growth that looks just like an onion or spring-onion leaf — round, smooth and silvery-green. It stands taller than the healthy leaves around it, and that shoot will never carry a head of grain.
The whole hill looks wrong
a badly hit plant stays short and grassy and throws out lots of extra thin shoots to replace the lost ones — but many of those are galled too, so the hill is crowded with shoots yet carries almost no grain.
The midge itself is hard to see
the adult is a delicate, reddish, mosquito-like fly about the size of a rice grain (3–4 mm) that flies only at night and does not bite. The maggot that does the damage is a tiny pale-pink grub hidden down inside the tube, behind the leaf sheath — so you will almost always find the gall, not the insect. At the tip of an older silver shoot you may even spot the empty, papery skin the adult left behind when it flew off.
Tell it apart from the stem borer
a stem borer kills the central shoot and leaves a dead, dry, brown shoot ('deadheart') that pulls out easily, while gall midge leaves a living, hollow, silvery tube that stays standing and green.
Tell it apart from hunger (a nutrient shortage)
too little feeding yellows the whole plant evenly, while a silver shoot is one distinct, separate tube standing among otherwise green leaves — not a general yellowing.
Scout for it
When to look
watch hardest during tillering — the few weeks after the crop establishes, when the plant is throwing out its shoots. This is the stage the midge attacks, so this is when scouting counts. Look even harder after a spell of warm, cloudy, rainy, humid weather, which is exactly what the midge breeds in.
How to walk it
go right into the field — not just the edge by the path — and walk a big 'W' shape so you cross all four corners and the middle. Make about 10 stops along the 'W'.
What to check at each stop
look closely at a hill or two for silver shoots — the hollow, onion-like tubes standing up among the normal leaves — and count how many of the shoots you look at are galled.
The danger line — more than 1 silver shoot in 20 (5%):
if, while the crop is tillering, more than 1 shoot in every 20 you check is a silver shoot, the midge is above the safe level — act now on what you still can and plan hard for next season. Below that, keep checking every few days until tillering is over.
Control it
Prevent it — start with the right seed
Your single strongest tool is to plant a gall-midge-resistant or tolerant rice variety suited to your area. ('Resistant' = the plant shrugs the midge off; 'tolerant' = it still yields even when attacked.) Ask your extension officer or a trusted seed supplier which local varieties stand up to gall midge.
Plant early and all together with your neighbours
Get the crop through the tender tillering stage before midge numbers build up in the wet season. Avoid late or staggered planting, don't crowd the stand, and go easy on nitrogen fertiliser — a lush, dense, late crop is exactly what draws the midge in.
Cut off the midge's hiding places
Clear out volunteer ('ratoon') rice, wild rice and grassy weeds in and around the field — these are the alternate hosts (other plants the midge breeds on) that carry it into your crop. After harvest, plough in or burn the stubble and ratoons so the midge has no bridge to the next season.
Protect your free helpers, and rogue out galls
Tiny parasitic wasps (parasitoids — wasps whose young feed on the midge's eggs and grubs inside the galls) can wipe out most of a midge population on their own. So do not blanket the crop with broad insecticides, which kill these wasps and only make the next attack worse. Where you find silver shoots, cut them off and bury or burn them to stop new midges emerging.
Don't reach for a spray — it can't win this one
Once the galls show, no insecticide helps: the maggot is sealed inside the tube where no chemical reaches it. Worse, a broad poison kills the parasitic wasps and bees and puts the person spraying at risk — for no gain. If anyone tries to sell you a spray for gall midge, keep your money; and if you ever must spray this field for another reason, cover your skin, eyes and nose, spray in the cool of the day with the wind at your back, keep it off food, water, children and bees, and wash well afterwards.
If it keeps spreading, or you're too late — cut your losses
Keep cutting and burning every galled shoot and clearing grassy weeds to protect the healthy tillers that are left. When a field is badly hit, harvest the healthy tillers you have, then destroy the stubble and ratoons. For the next crop, switch to a resistant variety and plant early and all-together with your neighbours — that, not a sprayer, is what actually breaks the midge.
Catch rice gall midge before it costs you the harvest
This guide is the general answer. Divisi works out yours — the week to scout your own field for rice gall midge, and what to do the day you find it.
Crops it affects
Plan the crops it attacks
All planting calendars, country by country
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Frequently asked questions
How do I identify rice gall midge?
The tell-tale sign — the 'silver shoot':. where you expect a normal folded leaf, an attacked shoot instead pushes up a hollow, pale, tube-shaped growth that looks just like an onion or spring-onion leaf — round, smooth and silvery-green. It stands taller than the healthy leaves around it, and that shoot will never carry a head of grain.
When should I take action against rice gall midge?
more than about 5 percent of tillers showing silver-shoot galls during tillering
How do I control rice gall midge?
Prevent it — start with the right seed. Your single strongest tool is to plant a gall-midge-resistant or tolerant rice variety suited to your area. ('Resistant' = the plant shrugs the midge off; 'tolerant' = it still yields even when attacked.) Ask your extension officer or a trusted seed supplier which local varieties stand up to gall midge.
Which crops are attacked by rice gall midge?
Among the crops covered here: Rice.