Weed and Pest Control – SS1 Horticulture and Crop Production Lesson Note (Second Term)

Weed and pest control is the use of farm methods to stop weeds and pests from reducing the size and quality of a harvest.

Behavioural objectives

By the end of the lesson, students should be able to:

1. define weeds and pests;
2. state four harmful effects of weeds on crops;
3. name the four groups of pests and give an example of each;
4. describe cultural methods of controlling weeds and pests;
5. name the types of farm chemicals and state the safety rules for using them.

What is a weed?

A weed is any plant that grows where it is not wanted, such as grass growing in a bed of carrots.

What are the common types of weeds?

Weeds are grouped by leaf shape and by life span.

• Grasses: narrow leaves with parallel veins, as in Bahama grass and speargrass.
• Broad-leaved weeds: wide leaves with branching veins, as in goatweed and waterleaf (when it grows where it should not).
• Sedges: grass-like weeds with solid, three-sided stems, as in nutsedge.
• Annual weeds: complete their life cycle in one season, as in goatweed.
• Perennial weeds: live for many years and regrow from roots or stems, as in speargrass and Bahama grass.

Why are weeds harmful?

Weeds are harmful because they compete with crops for the things the crops need to grow.

• They take water and nutrients: they use the water and fertiliser meant for the crop.
• They block sunlight: tall weeds shade small seedlings, so the seedlings cannot make enough food.
• They hide pests: insects, rats and snakes shelter in bushy, weedy farms.
• They spoil the look of gardens: weeds make a flower garden or lawn look untidy.
• They raise the cost of farming: more labour or chemicals are needed to remove them.

What is a pest?

A pest is a living organism, mostly an insect or an animal, that bites, sucks or destroys crops.

What are the types of pests?

There are four groups of pests: biting and chewing insects, piercing and sucking insects, boring insects and vertebrate pests.

1. Biting and chewing insects: they have mouthparts that cut leaves, as in grasshoppers and beetles.
2. Piercing and sucking insects: they push a needle-like mouthpart into the plant and suck the sap, as in aphids and whiteflies.
3. Boring insects: they dig holes into fruits, pods or stems, as in the pod borer on beans.
4. Vertebrate pests: larger animals that eat the crop or harvest, as in rats, birds and monkeys.

What damage do pests cause?

• Holes in leaves: chewing insects leave leaves looking like lace.
• Fruit rot and early fruit drop: boring insects open the way for rot.
• Wilting and stunted growth: sucking insects remove sap from the plant.
• Spread of diseases: some insects carry disease from plant to plant, as mosquitoes carry malaria.
• Loss of stored and standing crops: rats and birds eat grain and seeds.

What is the difference between a weed and a pest?

A weed is an unwanted plant that competes with the crop. A pest is an animal that feeds on or damages the crop.

What is cultural control?

Cultural control is the use of good farming habits to reduce weeds and pests without using chemicals.

What are the cultural methods of controlling weeds?

• Hand pulling: pulling weeds out by the root with the hands.
• Hoeing: using a hoe to cut or scrape weeds off the soil.
• Mulching: covering the soil with dry grass so weeds get no light to grow.
• Crop rotation: changing the crop grown on a piece of land each season so weeds do not build up.
• Use of clean seed: planting seed free from weed seeds.
• Close spacing: planting crops near enough that their shade keeps weeds down.

What are the cultural methods of controlling pests?

• Timely planting: planting early so the crop is strong before the pest season starts.
• Hand picking: removing caterpillars and snails by hand and destroying them.
• Farm sanitation: keeping the farm clean and removing rotten fruits and crop residues that attract pests.
• Crop rotation: breaking the life cycle of pests that attack one kind of crop.
• Trapping and scaring: using traps for rats and scarecrows for birds.

What other methods of control are there?

Besides cultural and chemical control, farmers also use biological and legal methods.

• Biological control: using the natural enemies of a pest, as in ladybirds feeding on aphids.
• Legal control (quarantine): laws that stop infested plants or seeds from being moved into a new area.

What is chemical control?

Chemical control is the use of farm chemicals (pesticides) to kill weeds and pests when other methods are not enough.

• Last resort: use chemicals only when hands and tools cannot cope.
• Risk: chemicals can harm people, animals and water if used wrongly.

What are the types of farm chemicals?

There are four common types of farm chemicals: herbicides, insecticides, rodenticides and fungicides.

What are the safety rules for using farm chemicals?

1. Read the label: follow the dose and instructions on the container.
2. Wear protection: use a face mask, gloves and boots, and never spray in school uniform.
3. Mind the wind: never spray against the wind, or the chemical blows back into your face.
4. No eating: do not eat, drink or smoke while spraying.
5. Wash up: wash your hands and body with soap after spraying.
6. Store safely: keep chemicals away from the kitchen and out of reach of children.
7. Dispose of containers: never reuse empty chemical containers for food or water.

Which control method should you use?

Choose the safest method that will solve the problem.

Evaluation

1. Define a weed and a pest.
2. State four ways in which weeds harm crops.
3. Name the four groups of pests and give one example of each.
4. List three cultural methods of controlling weeds.
5. What is a herbicide? Name two other types of farm chemicals.

Assignment

1. Explain why chemical control is called the last resort. List four safety rules for spraying chemicals and give one cultural method of controlling pests.