Integrated Weed Management (IWM) includes five main methods of weed control. They are: preventive, cultural, mechanical, biological and chemical.
Preventive control minimizes the introduction of new weeds into an area by such measures as using weed-free seed and soils and removing flower heads before they have gone to seed.
Cultural control is made up of three parts: competition, which means that desired plants have the competitive advantage over weeds; rotation, which is the planting of different crops in the same field yearly; and smothering, wherein ground covers such as Pachysandra, are planted to help reduce weed growth in landscaped areas by smothering, which deprives weed seedlings from light, moisture, nutrients and space.
Mechanical control is comprised of: hand weeding, such as would be used in the home garden or new lawns; hoeing, which is most effective with shallow root systems of annual weeds; tillage which involves machinery, such as cultivators and rototillers and is best used to control weeds in row crops; mowing, which can reduce seed production and dispersal; smothering or mulching, as detailed earlier; and dredging or chaining, which is used in aquatic weed control by attaching chains and dragging them behind a boat, to pull out the weeds.
Biological control is comprised of three parts: classical control, which is the introduction of a control agent which naturally feeds on these weeds; inundative control which includes the introduction of natural enemies such as viruses and bacteria that would produce diseases in them; and herbivore management, which uses animals like sheep, goats, ducks or fish to graze selected areas.
Chemical controls include five parts: preplanting, which uses herbicides on prepared seedbeds, prior to the crops being planted; preemmergence, which uses herbicides after the crop has been planted but before the seedlings have emerged; postemergence, wherein the herbicide is applied after the crop or weeds emerge; and finally seed treatment, wherein seeds can be treated with chemicals and/or fungicides before planting occurs.