Weed Management lecture notes

1. PRINCIPLES OF WEED MANAGEMENT
Prepared By: Dr Pooja Goswami
Assistant Professor (Agronomy)
College of Agriculture, Balaghat

2. Principles of Weed Management:
Principles of weed control are;
a) Prevention
b) Eradication
c) Control
d) Management
1. Preventive Measures:-Prevention is a concept as well as a method approach of weed control
/management. The popular saying “Prevention is better than cure”. Of medical Sciences
could bit modified to “Prevention is better than intervention.” Prevention simply means
stopping weeds from infesting an area. Prevention requiresa set of practices rather than a
single peactice to tacle the introduction and spread of weeds Such areas may be local,
regional or national in size. No weed control programme is successful if adequate preventive
measures are not taken to reduce weed infestation. It is a long term planning so that the weeds
could be controlled or managed more effectively and economically than is possible where
these are allowed to disperse freely. Following preventive control measures are suggested for
adoption wherever possible & practicable.
(1) Use Weed free crop seeds:- one important way the weeds spread on the
farmlands is through crop seeds, contaminated with the weed seeds. Some weed seeds
always go with certain crop seeds, for example, Avena fatua and Brassica spp. with
small grains. The prevention of weeds that disperse with the crop seeds can be
achieved in two ways, viz. (I) by the production of weed free crop seeds at the
Government farms or at the farmer’s field itself, and (II) by cleaning the crop seeds of
weeds before storage as well as at the time of sowing.
(2) Avoid contamination of manure pits:- It is a common practice of adding mature or
even blooming weeds and their vegetative propagules to manure pits in the hope of
recovering their manurial value. In most cases the weed seeds do not lose their viability
in the manure pits and the resulting farm-yard manure serves as a notorious source of
adding weed seeds to crop land.
(3) Prevent Movement of weeds with other farm resources:- Do not permit livestock
to move from the weed-infested areas directly into clean areas because they can
always drop weed seeds and fruits attached to them or those ingested by them earlier.
The farm machinery, for similar reason, should be cleaned properly before moving it

3. from one field to another. Same is true of the movement of nursery stock, gravel, sand,
and soil from weed-infested areas to the new ones.
(4) Keep non-crop areas clean:- The irrigation and drainage ditches, fence lines, farm
boundaries, bunds, and other like un-cropped areas are often neglected by farmers.
These places offer a perpetual weed nursery for the cropped plots. This should be
prevented by extending the weed control efforts to non-crop areas on the farm.
(5) Keep vigilance:- A farmer should inspect his farm areas periodically for some
strange looking weed seedlings. The search for them should be extended into standing
crops even if herbicides or cultivators were used to control weeds there. No sooner than
any strange looking weed seedling are noticed, they should be uprooted by digging as
deep as their roots may have penetrated the soil, and the soil in these spots should be
treated with a suitable sterilant.
(6) Legal measures:- Legal measures are necessary to check inter-state and inter-
country movement of noxious weeds if the cost of having to control additional 21 alien
weeds is to be saved. Unfortunately, thus far, in most parts of the tropical and sub-
tropical world, noxious weeds have not been subjected to strict quarantine laws. This
has resulted in the introduction and spread of some of the costliest weeds of the world.
2. Eradication:-
Weed eradication is complete removal of all live plant parts and seeds of a weed
from an area, which may be a field/farm/village/geographical region, depending upon
the need. Although very attractive, it is a very expensive adventure sine it will often cost
more than the land was worth. Moreover, total destruction of weeds is considered
undesirable even from crop fields since many weeds harbor predators of crop pests, or
secrete in soil nematicides, while all of them hold soil nutrients against their leaching
losses during fallow periods. Heavy expense of weed eradication is justified against
noxious weeds such as Striga, Cuscuta, and Lantana spp., and some perennial weeds
likes Cyprus rotundus, Cynodon devtylon Convolvulus arvensis Circium arvense etc. to
prevent their dispersal to additional millions of hectares of useful land and water bodies.
Against the common weed, we employ only control measures. But when required, a

4. weed eradication programme should begin when the weed growth is still limited. Once
the weed has invaded large, continuous areas, its eradication becomes uneconomical.
The weed eradication is accomplished in more than one year; it requires intensive initial
efforts to destroy all plant parts followed by many years of vigilance to prevent the new
weed seedlings from establishing into adult plants. For eradication programme,
whatever chemical opted should be nonselective and should act through soil since soil
needs to be sterilized . Several soil sterilants e.g methyl bromide, metham, EPTC,
Naclo3, cloropicrin and dagomet (DMTT) for the purpose. In variance with it, weed
control is an every year, constant rate programme. Of course, with proper preventive
measures, efforts required to control weeds can be reduced to a very low level, in due
course of time.
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.
Weed Management:-
Weed control aims at only putting down the weeds present by some kind of physical or
chemical means while 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.
Management means to maintain/manage a population below threshold level
Weed control methods are grouped into cultural, physical, chemical and biological.
Every method of weed control has its own advantages and disadvantages. No single
method is successful under all weed situations. Many a time, a combination of these
methods gives effective and economic control than a single method.