1. What is a Weed? A weed is a plant that is growing where it is not wanted, it can have strong and healthy growth, and is able to overgrow valued plants by overcrowding, thus depleting soil nutrients and moisture that would otherwise be available to preferred plants.

2. Examples of weeds Dandelion

3. English Plantain

4. Nettle

5. Poppy as a weed in a field of crops

6. Poppy as a wanted plant in a garden

7. Prickly Pear Cactus

8. Area in Queensland, Australia, covered with prickly pear cactus (Opuntia stricta), which had expanded rapidly after being introduced in 1926.

9. The same area three years later (1929) after the cactus moth (Cactoblastis cactorum) was introduced as a biological control agent for the cactus.

10. Use of pesticide in crop spraying

11. Spraying DDT to get rid of mosquitoes