Grade 10 Agriculture – Crop Protection: Weed control Quiz

Striga is a parasitic weed that attaches to maize roots, sucking water and nutrients and causing severe stunting and yield loss. The others are competitive or invasive but not root-parasitic on maize.

Changing crops alters the growing conditions and planting times, interrupting weeds adapted to a particular crop. It does not instantly remove all seeds or make herbicides obsolete.

Pre-emergence herbicides are applied to the soil to prevent weed seeds from germinating. Other options describe times unrelated to the pre-emergence use.

Hand hoeing is affordable and effective for smallholder plots in Kenya. Aerial spraying and soil steaming are impractical or expensive; weekly deep ploughing is unnecessary and may damage soil structure.

IWM uses multiple complementary methods to manage weeds sustainably. Relying only on herbicides or monoculture increases weed problems over time.

Young crops have limited root and canopy development, so early weed control prevents yield losses. Weeds continue to grow later if not controlled.

Biological control uses living organisms to reduce weed populations. Fertilizer, burning, or herbicide application are not biological methods.

Continuous use of the same mode-of-action selects for resistant weed biotypes. While herbicides can affect non-target organisms, resistance development is the key risk.

Purple nutsedge has underground tubers (nutlets) that resprout if not completely removed. Striga is parasitic, but does not regrow from tubers; amaranthus and clover do not have such tubers.

Velvet bean grows quickly, shades the soil, outcompetes weeds and adds organic matter and nitrogen. Leaving land bare or continuous monoculture encourages weeds rather than suppressing them.

Selective herbicides target certain weed species (e.g., broadleaf weeds in cereals) while sparing the crop. Non-selective herbicides kill most plants they contact.

The weed seed bank is the reservoir of viable weed seeds in the soil; managing it is key to long-term weed control. The other options are incorrect definitions.

Seeds hitchhike on tools, boots and machinery; cleaning reduces spread. The other practices may actually help spread weeds or have unrelated effects.

Weeds compete for light, nutrients and water, leading to stunting and reduced yield. Better growth or no change would not indicate harmful weed competition.

Immediate thorough rinsing and removing contaminated clothes reduces exposure. Wiping with soil, delaying washing, or using diesel are dangerous and ineffective.

Early weeding prevents weed competition when the crop is young. Weeding after weeds are mature or after harvest is too late to prevent yield loss; heavy rain makes hoeing ineffective.

Mulch forms a physical barrier, suppressing weed emergence and conserving moisture. It does not chemically burn weeds or intentionally increase weed germination.

Parthenium causes dermatitis and respiratory problems and is a troublesome invasive. Clover and sesbania are not typically allergenic in the same way; volunteer maize is simply crop seedlings.

Conservation tillage leaves residues that suppress weeds and maintain soil health. It does not instantly kill all weeds or prevent moisture entry; its goal is balance between weed and soil management.

Managing Striga requires integrated approaches including resistant varieties, crop rotation (especially with non-hosts), and good crop establishment. Single herbicide use is ineffective for root parasites; irrigation won't reliably control Striga.

Hand-weeding reduces chemical exposure but needs labour; herbicides reduce labour but pose risks if misused. The other statements are false.

Using multiple control tactics and rotating herbicide modes of action reduces selection pressure for resistance. Repeated use of the same herbicide promotes resistance.

Cultural practices modify crop management (e.g., spacing, timing) to disadvantage weeds. Spraying timing, burning, or leaving residues are not standard cultural practices for shading-based suppression.

Labels provide correct dosage, timing, safety precautions and crop compatibility to prevent misuse. They are not optional or secret and mixing chemicals without guidance is dangerous.

Organic systems avoid synthetic herbicides; manual weeding and organic mulches are suitable alternatives for organic farmers.

Allowing weeds to set seed replenishes the soil seed bank, worsening problems in following seasons. The other choices are incorrect outcomes.

A weed is any plant growing in a place where farmers do not want it and that competes with the crop for light, water and nutrients, reducing yields.

Weeds compete with crops for essential resources such as water, light and nutrients, which reduces crop growth and yield, especially on small farms with limited inputs.

Striga (witchweed) is a parasitic weed that attaches to roots of cereals like maize and sorghum, causing severe yield losses in Kenya if not managed.

Pre-emergent herbicides are applied to the soil surface or incorporated before weeds emerge to stop germination or kill seedlings as they sprout.

Post-emergent herbicides are applied to actively growing weeds (after emergence) and may be selective or non-selective depending on the product.

Selective herbicides target certain weeds while leaving the crop largely unharmed, making them useful in crops like maize or tea when used correctly.

IWM combines methods—such as crop rotation, timely hand weeding, mulching and careful herbicide use—to control weeds sustainably and reduce resistance.

Weeding early—often within the first 3–6 weeks for many crops—reduces competition and prevents weeds from producing seeds that replenish the weed seed bank.

Mulches (e.g., crop residues) block light and reduce weed germination while helping conserve moisture and improve soil conditions for crops.

Rotating crops changes planting times, canopy cover and soil disturbance, which can reduce weeds that are adapted to a single cropping system.

Repeatedly using herbicides that act the same way selects for weeds with genetic resistance; rotating herbicide modes and methods reduces this risk.

PPE such as gloves, long clothing, boots and a mask protect the applicator from skin contact and inhalation of toxic herbicide sprays.

Calibration helps measure output per area so the correct herbicide rate is applied—too much can harm crops and too little can give poor weed control and resistance.

The weed seed bank is the reserve of viable weed seeds in the soil; managing it (by preventing seed set) reduces future weed problems.

Mechanical control includes physical removal of weeds such as hand pulling, hoeing or tillage to uproot and destroy weeds.

Allelopathy involves plants releasing natural chemicals that inhibit other plants; farmers can sometimes use allelopathic cover crops to reduce weeds.

Resistant varieties and rotations with legumes or trap crops reduce Striga seed banks and interrupt its life cycle, helping control this parasitic weed.

Weed seeds hitchhike on tools and boots; cleaning prevents transferring seeds and reduces infestation risk on other farms.

Dry crop residues or grass form a mulch layer that blocks light and suppresses weed germination while conserving moisture. Fresh wet weeds can decompose and allow weeds to regrow.

Weeds can mix seeds and debris with the crop at harvest, reducing quality, market value and sometimes causing additional drying or storage problems.

Pre-emergent herbicides work best when applied at planting or soon after to prevent weed seeds from germinating and establishing.

Regular removal of weeds by hand or slashing plus mulching reduces competition and pest habitats in perennial crops like tea and coffee without harming the crop.

The critical period is the crop growth stage during which weed control is essential to prevent yield reductions; managing weeds outside this window has less effect on yields.

Purple nutsedge reproduces from underground tubers (nutlets) that persist after removal; control requires removing tubers, repeated weeding or appropriate herbicides.

Weeds treated with herbicide can carry residues. The label gives safe disposal instructions—do not feed to animals or compost if residues persist; bag, burn or bury as recommended to protect people and environment.