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Weeds are the quiet thief of a wet year. Leave them in your maize all season and they can cut your yield by 22-41% — but you only have to win the first few weeks, and this guide shows you exactly how.
More rain means more money on the table, and more weeds racing you for it. On a plot that would fill 20 x 90 kg bags of maize, that 22-41% loss is roughly 4 to 8 bags gone — income you never see. Here is how to keep the harvest yours.
Why are there so many more weeds in my maize this wet year?
Warm, wet El Niño soil wakes up far more weed seeds, so they sprout thicker and grow back faster every time you clear them.
Weeds are not just untidy — they steal exactly what your maize needs:
- Water: weeds can take 20-40% of your soil moisture.
- Food: they can rob 30-50% of the fertiliser you apply — in one cereal trial, weeds stripped about 46 kg of nitrogen per hectare in the first five weeks, plant food that should be building your maize.
- Light: tall weeds shade young maize, leaving it thin and weak.
Zone note: In the moist savanna and highlands, grasses and broadleaf weeds explode after heavy rain. In the drier Sudano-Sahelian and semi-arid zones, the bigger enemy is Striga on tired soils — more on that below.
How long do I need to keep my maize weed-free?
As a widely used rule of thumb, keep your maize clean for roughly the first 3 to 6 weeks after it comes up — about the 3-to-8-leaf stage. This is the critical weed-free period: weeds that grow with the crop in this window do the most damage, and clearing them here protects almost all your yield.
Photo: Sergej / Pexels
No-tool field rule: your maize should always stand taller than the weeds around it in the first six weeks. If the weeds are reaching the height of your maize leaves, you are already late.
Beat weeds before they start — the stale seedbed:
- Prepare your land and let the first rains or a light watering wake the weeds.
- Wait 1-2 weeks for that first flush to sprout.
- Kill it shallow with a hoe (deep hoeing only brings up more seeds) or a knock-down spray.
- Plant into a much cleaner bed.
This empties the top of your soil's weed "seed bank" before your crop is even up.
Is it better to hand-weed or use herbicide?
Both work — the best method is the one you can finish on time. Late weeding is the biggest yield-loser: hand-hoeing one hectare (2.5 acres) takes about 300-400 hours, roughly 40-50 labour-days — so line up your labour before the rains, not after.
Photo: Magda Ehlers / Pexels
| Method | Labour per hectare (2.5 acres) | Best for | Watch out for |
|---|---|---|---|
| Hand hoe | ~300-400 hours (40-50 labour-days) | small plots, close work around plants | back-breaking; easy to fall behind in a wet year |
| Animal-drawn cultivator | as little as ~40 hours (about 90% less) | wider rows, larger plots | space rows for the animal; still hand-weed within the row |
| Herbicide + one cultivation | ~31-34 hours (about 90% less) | on-time control within the first 6 weeks when labour is short | read the label, wear protection, correct dose |
(Labour figures: FAO.)
Mulch to smother weeds: a thick layer of dry grass, maize stover or leaves blocks light so fewer weeds sprout, and it holds the rain your maize wants. Be honest about the trade-off: without enough mulch or herbicide, total labour under conservation agriculture can climb — one Zambian study found it rise from 27 to 81 labour-days per hectare, with hand-dug planting basins the most labour-hungry method. So keep at least about 30% of the soil surface covered (roughly 2-3 tonnes per hectare of dry grass or stover) and pair mulch with early weeding while it builds up. See building soil that holds water and conservation agriculture.
What is the purple weed with pink flowers in my maize?
That is Striga hermonthica — purple witchweed — a parasite that plugs into your maize roots and drinks its food and water. It costs African farmers about US$1.2 billion a year and attacks nearly a quarter of the continent's maize land.
How to spot it in the field:
| What to check | What Striga shows |
|---|---|
| Flowers | small bright pink to rose-red flowers, 6-10 on a spike |
| Plant | slender, 30-100 cm tall |
| When & where | emerges 3-6 weeks after your maize, in patches on the poorest, driest soil |
| Your maize | yellows and wilts even when it rains — the theft is underground; bad patches lose 30-100% of the crop |
Why it's stubborn: each seed pod holds several hundred seeds and one plant carries many pods — so a single Striga plant sheds tens of thousands of dust-fine seeds that can survive 10-20 years in the soil. So the goal is to stop it seeding and starve it out over seasons:
- Pull it by hand before it flowers, and burn it — never let it set seed.
- Feed your soil. Striga thrives on tired, low-fertility land; manure and nitrogen weaken it.
- Rotate or intercrop with a legume or trap crop — cowpea, groundnut, soybean or cotton — that makes Striga seed germinate and die with no maize to attach to.
- Push-pull: intercrop maize with Desmodium (a legume). Its roots trigger "suicidal germination" of Striga seed, and farmers report three to four times more maize. It also cuts stemborer and fall armyworm.
- Ask your agro-dealer for Striga-tolerant (IR) maize seed for badly infested land.
How do I spray weed killer without damaging my maize?
Herbicide is one good tool — not magic. Used with one cultivation it can cut weeding to about 31-34 hours per hectare, but the wrong dose wastes money or scorches your crop.
- Match type to timing: pre-emergence goes on clean, moist soil before weeds and maize show; post-emergence goes on small, growing weeds.
- Read the label, every time — the crop, the dose per litre and per hectare, and the pre-harvest interval (the days between spraying and harvest). Measure, don't guess; more is not better.
- Calibrate with no tools: fill your knapsack with 15 litres, spray a measured strip at your normal walking pace, and see the area it covers. Now you know your litres per hectare and can mix the label rate correctly.
- Protect yourself (PPE): gloves, covered arms and legs, closed shoes and eye cover; spray with the wind behind you; never clear a blocked nozzle with your mouth; wash with soap after.
Your next step this week
Walk your maize today and check one thing: is the crop taller than the weeds? If not — or if the first weeds are breaking through — weed now, this week, while you are still inside that critical first-six-weeks window. Line up your labour or your sprayer before the next big rain, not after it.
