Weeds have been known since the ancient times. Weed are unwanted plant that grow along with the main crop in the field. Weed are considered as cumbersome for successful agriculture production. Due to crop-weed competition the crop yield losses are generally high in agriculture production. So, in order to minimize such losses farmers are practicing several weed management strategies which includes prevention, eradication, control (mechanical, cultural, biological and chemical method). The cultural methods are expensive and time consuming so, farmer have to move towards other alternative methods of weed control Varga et.al (2000). Furthermore, due to rising labor cost and non-availability of labor for manual weeding during the critical period of weed control has contributed to use of herbicides. Herbicides not only timely and effectively controls the weed but also offer a great scope for minimizing the cost of production Varga et.al (2000). Control methods are applied after the emergence of weed on the field while prevention methods of weed control are adopted before sowing the crops. Generally, there are two objectives: 1. To prevent the entry and establishment of weed species in an area.2. To prevent the spread of weed or to limit the weed build up in a field. These objectives are referred as prevention. And any method that are applied before sowing the crop to prevent there entry , establishment and spreads comes under the prevention category. Focusing on second objective of preventive measures of weed control we can say that some cultural methods such as crop rotation or crop diversification, stale seed bed, tillage system, cover crops ( used as green manures or dead mulches),soil solarization, irrigation and drainage systems and crop residues managements can be included under preventive methods of weed control. In practice, weed management strategies should integrate indirect (preventive) methods with direct (cultural and curative) methods. The first category includes any method used before a crop is sown, while the second includes any methods applied during a crop growing cycle. Methods in both categories can influence either weed density (i.e., the number of individuals per unit area) and/or weed development (biomass production and soil cover). However, while indirect methods aim mainly to reduce the numbers of plants emerging in a crop, direct methods also aim to increase crop competitive ability against weeds.The success of prevention depends on awareness of the problem, species, effort, Co-operation, area. •Most effective where adopted against a single species on a large area on a cooperative basis. In conclusion we can say that farmers have several preventive methods in their arsenal that they can put together to build up a good weed management strategy. Preventive weed control is permanent weed control and usually require community action. it. For this process, a collective or joint effort and commitment is required.

1. Preventive measures of weed control
Presented by :
Sudha Neupane
Department of agronomy
AFU, Rampur, Chitwan

2. Introduction
•Weeds may be defined as plants other than crop plant or any unwanted plant grown in
the main field with crop plants.
•Weeds not only grow with the main crop but also compete with main crop for basic
necessities like sunlight, nutrients, space and water etc. and cause a yield reduction in
agricultural production (Das 2008).
•Weeds interface with utilization of natural resources, are harmful, prolific, persistent,
competitive, and even poisonous, economically detrimental and can grow under adverse
climatic conditions.
• Some weeds release toxins that inhibit crop growth; others may harbor insects, diseases,
or nematodes that attack crops.

3. •Yield losses caused by weed (33%) accounts more than any other agriculture
losses caused by pathogens (26%), insect pests (20%), storage pests (7%),
rodents (6%) and others (8%) in India (Yaduraju et al. 2015).
•Weeds account for about one-third of the total losses caused by agricultural pests
(DWR, 2015).
•Weeds are impossible to totally eliminate from the main field as they spread
through many ways like dispersal of dormant seeds, vegetative propagules etc.
(Singh et al., 2014).
•So, as to prevent the losses caused by weed it is essential to follow effective
weed management strategies.

4. Objective
 To study the preventive measures of weed control
 To study the merits and demerits of preventive measures of weed control
Methodology
The study was carried out using the secondary sources of data. Rigorous desk study was
conducted for the literature collection on Preventive weed control. Various research papers,
review articles, and reports studied thoroughly for the compilation of this study. The study
aimed at knowing about the preventive measures of weed control.

5. Pre-requisite of a successful weed management programme
• Knowledge of the biology of weeds
• Nature of weed problem
• Must be planned for the whole farm
• Must follow up programme of weed prevention measures

6. Steps taken prior to choosing weed control strategy
• Identify the weed problem
• Know what control methods are available
• Evaluate the benefit/risk of each method/combination of methods
• Choose the methods: most effective with least harm to himself and environment
• Know the correct use of weed control method

7. Weed management strategies
• Preventive Measures
• Eradication Methods
• Management/Control Methods

8. Prevention: Prevention means stopping a new weed from invading an area or
limiting a weed buildup in a field.
• Preventive measures includes all measures to deny the introduction,
establishment and spread of weed.
• All practices that help discourage the weeds from becoming a problem over time, form
the subject of weed prevention.
• No weed management programme can be successful if adequate and timely preventive
measures are not taken.

9.  One year of seeding is seven years of weeding
• Nature has provided weeds with a number of devices that help them to be disseminated
widely.
• The troubles that weeds create in crops, soil and water bodies are therefore, summed in
the adage ‘one year of seeding is seven year of weeding’.
Prevention is better than cure
• To avoid a situation of one year of seeding is seven years of weeding, a wise step is to
follow the principle of ‘Prevention is better than cure’.
• Keeping in view the economic and practical feasibility, the preventive weed management
measures should be followed to check their menace.

10. Preventive measures of weed control
1.Quality seed: The first and the most important weed management approach in any crop
is the use of clean crop seed. The seed contaminated with weed seed is a good source of
spread of weeds. It becomes hard to separate the weed -seed from the crop seed.
• For example, cruciferous crops like radish, cauliflower, cabbage, broccoli etc. are well
mixed with the seed of (Argemone Mexicana) .Crop seeds infested with weed seeds may
introduce problematic weed species to a new field and increase the seed numbers in the soil
weed seed bank.
• Thus, crop seed that is free from weed seed should be sown to prevent the entry of weed in
new areas.

11.  Weed free crop seeds may be produced by following the pre-cautionary measures:
 Separating crop seeds from admixture of crop & weed seeds.
 Using air-screen cleaners & specific gravity separators.
 Through means of Seed certification.
 Weed laws are helpful in reducing the spread of weed species & in the use of well adapted
high-quality seeds.
 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.

12. 2. Clean implements
• While operating agricultural implements like cultivator, harrow, and seed drill etc.
in weed infested field, care must be taken that multiplication part of weed such as
rhizome, bulb, tubers, stem is not being carried along.
• The machinery used for tillage, sowing, harvesting, or threshing operations should also
be cleaned before moving it from one field to another.
• The agricultural implements should be cleaned properly before use. Only then these
should be used in other fields. This will helps in controlling spread of the weeds.

13. 3.Removal of weeds along canal and irrigation channel
• Weed seed get transported through water and reach the field. Removal of weeds
growing along the sides of canal or irrigation channel is necessary to prevent weed
invading in the field.
• Periodical clearance of weed vegetation established along canal and irrigation channel
prevents it from invading the field.
4.Care in transplanting of seedling/plantlets: Many horticultural plants like
all transplanted vegetables, flowers, and fruits are transplanted in the field with soil
attached to their root. Infestation of soil with weed may contaminate a new field. While
purchasing nursery plants ensure that the nursery is free from weeds. (Avoid weed seed
entry via earthen balls).

14. 5. Use of well rotten manure: Weed seeds have good viability & may also remain viable after
passing through animals resulting in contaminated manure.The seed of (Convolvulus arvensis )
remain viable for as long as 50 years. Doob (Cynodon dactylon) and motha (Cyperus rotundus) seed
viability lasts for two and five years, respectively. Screenings used for feed should be finely
ground, cooked or pelleted to ensure destruction of all the weed seeds
• For making manure the cow dung is generally heaped. If the heaping period is short, the seed do not
lose its viability and grows in the field whereever manure is applied. So only well rotten FYM
should be used.
• Composting temperature of 65-95ºC should be maintained for 4-5 months to devitablize weed
seeds.
In addition to FYM Vermicompost may also be a potential source/medium of weed seed dispersal.

15. Weeds Infesting FYM

16. 6.Avoiding passing of cattle from weed infested area: Grazing
in weed infested field followed by allowing passage of cattle in new field favors
dissemination of weed seed.
• Some weed seeds such as Bidens Pilosa, Spiny pigweed and stick to the legs and skin of
the animals and get transported to some other place where it germinates and grow as
a weed.

17. 7. Quarantine Laws: Plant quarantine is defined as the legal enforcement of the measures
aimed to prevent pests or weed from spreading or to prevent them from multiplying further
in case they have already gained entry and have established in new restricted areas.
Quarantine laws impose legal restrictions on the movement of the agricultural material. If
there were adequate quarantine laws, the Parthenium and Argemone which widely grows
in vegetable and flower field may not have entered Nepal. Creating isolation between
widely weed infested area and new area is essential by enforcing and observing quarantine
properly.

18. Table no 1: Classification of cultural practices potentially applicable in an integrated weed
management system for organic farming, based on their prevailing effect.
Source: Barberi,(2002), https://www.fao.org/3/y5031e/y5031e0e.htm

19. Success of prevention depends on-
•Awareness of the problem
•Species
•Effort
•Co-operation
•Area
•Most effective where adopted against a single species on a large area on a cooperative
basis

20. Merits of preventive measures of weed control
1. Eradication of noxious weeds
2. Easier maintenance and lower the cost of production.
3. More permanent control of weed.
4. Elimination of traffic hazards
5. Elimination of health hazards
6. Improved utility services
7. Improved beauty

21. Demerits of preventive measures of weed method
1. Preventive weed programs usually require community action through enactment and
enforcement of appropriate laws and regulations.
2. Practical difficulty in adoption.
3. Immediate and quick weed control is not possible.
4. The success of preventive weed management programs varies with weed species, its
biology, means of dissemination and the amount of effort needed to be applied.

22. Conclusion
Farmers have several preventive methods in their arsenal that they can put together to
build up a good weed management strategy.
Preventive measures of weed control is permanent weed control and usually require
community action.
 For this process, a single year and single man approach will not work rather a
collective or joint effort and commitment may be required for more than a year is
required for the success of preventive weed control methods.