How weeds spread.
Weeds spread by seed, seed is easily dispersed by the wind, or by birds. Burrs, bulblets and roots are other methods.
Weeds are either monocots or diocots. Monocots have one leaf on germination, usually parallel veins (most grasses are monocts) . Diocots are broad leaf weeds such as clover, these have a network of veins.
Weeds may be annuals, biennials or perennials.
Annual weeds live for one year and then die, they are spread by seed. So prevent seeding.
Biennial weeds produce seed in their second year of life. So again prevent seeding.
Perennial weeds are root based, or bulb based, they can seed and also spread by runners or bulbs. Breaking and dropping roots when removing them can cuase further spead. You need to prevent seeding and destroy or remove the root system.
NON CHEMICAL CONTROL
Hand weeding is encouraged as this can be done at any time and saves on chemical use.
Mulching is a great way to prevent weeds from growing.
Close planting, weeds love open ground so close planting can help supress weed spread.
Check introduced plants and (potted plants) for weeds.
Prevent weeds from flowering, dig, cut mow or cut but do not let them flower.
Use a hoe to dig weeds to the surface on a hot day, this can kill roots.
See a weed, remove it as soon as possible, before the root system develops.
By far the most popular chemical controls are Selective weed killers and Systemic weed killers based on glyphosate.
Selective weed killers taget different weeds, such as bindi and clover, or broad leaf weeds.
Systemic weed killers will kill just about anything they come into contact with.