Principles of weed control are;

a) Prevention

b) Eradication

c) Control

d) Management

A. Preventive weed control

• Avoid using crop that are infested with weed seeds for sowing
• Avoid feeding screenings and other material containing weed seeds to the farm animals.
• Avoid adding weeds to the manure pits
• .Clean the farm machinery thoroughly before moving it from one field to another. This is particularly important for seed drills
• Avoid the use of gravel sand and soil from weed-infested
• Inspect nursery stock for the presence of weed seedlings, tubers, rhizomes, etc.
• Keep irrigation channels, fence-lines, and un-cropped areas clean
• Use vigilance. Inspect your farm frequently for any strange looking weed seedlings. Destroy such patches of a new weed by digging deep and burning the weed along with its roots. Sterilize the spot with suitable chemical.
• Quarantine regulations are available in almost all countries to deny the entry of weed seeds and other propagules into a country through airports and shipyards.

Weed free crop seeds

It may be produced by following the pre-cautionary measures:

• Separating crop seeds from admixture of crop & weed seeds using physical differences like size, shape, colour, weight / texture & electrical properties.
• Using air-screen cleaners & specific gravity separators, which differentiate seeds based on seed size, shape, surface area & specific gravity.
• Through means of Seed certification we can get certified seeds and can be used safely because the certified seeds contain no contaminant weed seeds
• Weed laws are helpful in reducing the spread of weed species & in the use of well adapted high quality seeds. They help in protecting the farmers from using mislabeled or contaminated seed and legally prohibiting seeds of noxious weeds from entering the country.
• Quarantine laws enforce isolation of an area in which a severe weed has become established & prevent the movement of the weed into an uninfected area.
• Use of pre-emergence herbicides also helpful in prevention because herbicides will not allow the germination of weeds

B. Eradication (ideal weed control rarely achieved)

• It infers that a given weed species, its seed & vegetative part has been killed or completely removed from a given area & that weed will not reappear unless reintroduced to the area.
• Because of its difficulty & high cost, eradication is usually attempted only in smaller areas such as few hectares or few thousand m2 or less.
• Eradication is often used in high value areas such as green houses, ornamental plant beds & containers. This may be desirable and economical when the weed species is extremely noxious and persistent as to make cropping difficult and economical.

C. Control

• It encompasses those processes where by weed infestations are reduced but not necessarily eliminated.
• It is a matter of degree ranging from poor to excellent. In control methods, the weeds are seldom killed but their growth is severely restricted, the crop makes a normal yield.
• In general, the degree of weed control obtained is dependent on the characters of weeds involved and the effectiveness of the control method used.

D. Weed management

• Weed management is a system approach whereby whole land use planning is done in advance to minimize the very invasion of weeds in aggressive forms and give crop plants a strongly competitive advantage over the weeds.