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SATSA Mukhapatra - Annual Technical Issue 18 : 2014
48
ISSN 0971-975X
Invited Paper
Weed Prevention for Quality Seed
Production of Crops
B. Duary*
(Received: January 15, 2014; Revised: January 31, 2014; Accepted: February 09, 2014)
Department of ASEPAN, Institute of Agriculture (Palli Siksha Bhavana), Visva-Bharati, Sriniketan 731 236,
Birbhum, West Bengal, India, *E-mail: bduary@yahoo.co.in
ABSTRACT
Weed management is the most important aspect while producing good quality
seed and maximizing crop yields. Weed problems start with weed seeds. The weed
seed contaminants in crop produce cause quality deterioration and weed seeds in grain
crops perpetuate when the seed is replanted. Global climate change, increased use of
tractor and power tiller, intensive cultivation etc. have been aggravating weed problems.
Again problem of specific weeds like
Echinochloa crusgalli, E. glabrescens
and weedy
rice in rice;
Phalaris minor, Avena ludoviciana
and
Lolium temulentum
in wheat; and
many vegetatively propagated weeds in other crops have been a great concern to the
farmers. An integrated approach must be used to effectively manage weeds. Among
different management approaches, weed prevention is most effective to deal with
weeds. There are many ways to prevent weeds in agricultural activities like preventing
introduction through contaminated seed / feed and movement of machinery / farm
animals, use of well decomposed farm yard manure / compost, keeping irrigation
channels and surroundings clean, managing weeds in nurseries, enforcement of plant
/ weed quarantine laws etc. With perspective to globalization, quarantine will play an
important role in checking the entry of new weeds. In recent past, five quarantine
weeds have entered in India through food grains imported with relaxed phytosanitory
condition and distributed through public distribution system. Some of these have already
been detected in southern states of the country. Therefore, the first and foremost step
is to prevent the entry of new weeds in new areas.
Key words : Crop seed production, Objectionable weed, Quality seed, Quarantine
weed, Weed prevention.
Introduction :
Weeds are omnipresent. It is a part of
each and every agro-phytocoenosis. Weeds
continue to be a perennial and constant threat
to agricultural productivity and profitability
despite decades of research and development
SATSA Mukhapatra - Annual Technical Issue 18 : 2014
49
of modern weed management practices for
their elimination. Recently the problems of
weeds are being aggravated due to many
reasons like shortage / high wages of labourers
especially with the introduction of National
Rural Employment Guarantee Scheme in India
and non-availability of suitable weed
management tools and implements in the
hands of farmers, climate change, import of
food grains etc
.
The increased use of power
tiller and tractor has aggravated the problem
of weeds like
Commelina benghalensis, C.
nudiflora, Marsilea quadrifolia, Paspalum
scorbiculatum, Jussiaea repense, Cardenthera
uliginosa
and
Cynodon dactylon
which
propagate mainly through vegetative means
(Duary and Mukherjee, 2013). While passing,
these machines cut and make these weeds
into pieces which further grow and multiply
as separate individuals. Many new weeds
which were less important are emerging in a
big way. Weeds having mimicry with crops
like
Phalaris minor
,
Avena ludoviciana
and
Lolium
temulentum
in wheat, and weedy rice,
Echinochloa colona
,
E. crusgalli
,
E. glabrescens
,
Sacciolepsis
sp. in rice are emerging as a big
threat as they are not manageable by farmers’
existing manual method of weed management.
The term ‘weed’ always has a negative
connotation not only by its presence as a plant
but as a seed also. Actual weed problems start
with weed seeds. The weed seed contaminants
in the crop produce cause quality deterioration
and weed seeds in grain crops perpetuate
when the seed is replanted. Weed seeds serve
as a primary source of new populations on
the site of their production or elsewhere. Weed
problems would be much less complicated if
weed seeds merely fell off plants and gravity
alone determine their destination. The
colonization of new areas by most of the weeds
is by movement of weed seeds. Once seeds
have been produced, they disperse in space
by several methods. The opportunity for
biological invasion begins with seed dispersal,
and many weed species possess well-adapted
appendages to assist in long distance
movement of their seeds. The movement of
most of the weeds from one location to the
other is mainly through their seeds. In nature,
their distribution is facilitated by winds, water
or animal’s movement. However, globalization
and World Trade Organization (WTO) regime
result into the free flow of food grains and
other commodities across borders that enhance
the possibility of movement of weed seeds
along with food grains from one country to
other. The rapid spread of weeds by human-
induced mechanism seems to be the important
one for weed spread and even greater than
that of most natural mechanism including those
of water, wind or animals. Human-induced
spread is now considered to be the main reason
for new weed incursion globally (Mack and
Lonsdale, 2001; Adkins, 2013). Survival of
any weed species depends on production of
sufficient number of viable seeds, and
therefore, prevention of entry of weed seeds
and seed production is the key to eliminate
the future weed problems. Failure to prevent
SATSA Mukhapatra - Annual Technical Issue 18 : 2014
50
seed entry and seed production of weeds results
in increasing number of seeds in soil, weeds
in each crop and weed seed contaminants in
crop produce.
Weeds compete for light, space, CO2,
nutrient, moisture etc
.
and share with essential
resources which are limited to the particular
habitat and ultimately reduce the growth, yield
attributes and yield of crops. Any plot for seed
production should be kept weed free to avoid
weed seed contamination. Controlling weeds
in a seed production plot is crucial, because
weeds result in a loss of crop yield and quality.
Weeds also act as alternate hosts for insects
and diseases, reduce nutrient use efficiency,
lower the efficiency of irrigation system and
impair quality and quantity of harvest. Other
important ways of interference are by
allelopathy, increasing cost of seed production
due to additional cost involved in weed removal
/ control. The quality is affected due to weed
interference by reduction of size, shape, colour,
weight of individual seed etc
.
by competition
as well as by admixture of weed seeds with
crop seeds.
Importance of Weed Prevention :
Weed management is important in seed
production in order to produce high quality
seed and maximize yields. During seed
cleaning and conditioning, large amounts of
valuable crop seeds can be lost when removing
weed seeds. All management factors such as
field selection, crop rotation, tillage, seed
source, cultivation, irrigation, herbicides and
harvest methods must be used together
(integrated) to effectively control weeds.
Among these, weed prevention is the most
effective method of dealing with weeds. Once
a weed has entered into an area and becomes
established, eradication is far more expensive
and it is likely that greater resources will be
required to control its further spread and reduce
its impact. The first step in weed prevention,
and the most cost-effective means of
managing weeds is preventing the entry of
new weeds. It is much easier to treat weeds
when present in small numbers than when they
are well established. The importance of weed
spread prevention has grown with the
recognition that the spread of most weeds
occurs through similar pathways, such as the
movement of goods, animals and vehicles
contaminated with weed seeds.
Ways of Weed Prevention :
There are many ways to prevent weeds in
agricultural activities which are well known
including restricting the opportunity for new
weeds to invade and spread. Some important
of these are as follows:
Preventing introduction through
contaminated seed and feed :
It is always advised to use clean and pure
seeds of crops as possible. Seed should be
certified and purchased from some authentic
sources. The local market seed should be
avoided or must be cleaned properly before
sowing. Some of the weeds have mimicry while
seed formation and often results in the harvest
of weeds with crop and thus mixing of weed
seeds goes on year after year. A typical
example is
P. minor
in wheat seed production.
SATSA Mukhapatra - Annual Technical Issue 18 : 2014
51
There are also several weeds, called satellite
weeds, whose seeds are exactly similar in
shape, size and look with that of crop seeds
and it is very difficult to separate them out
once mixed with the crop seeds. This similarity
is responsible for unwanted admixture of crop
and weed seeds. Recently, as high as 100 g
of seeds of
P. minor
in 5 kg of wheat grain
have been detected in West Bengal from the
wheat samples collected from different
households supplied through public distribution
system (PDS). The food grains are mainly
supplied from north-western India where
P.
minor
has developed resistance to isoproturon,
sulfosulfuron, clodinafop and other herbicides.
The imported food grains are distributed
through PDS and spread from household
surroundings to crop field
via
manure pits.
Again some farmers use the food grains
received mainly for consumption purpose as
seed materials by misconception and thus the
weed seeds enter into the crop field. Not only
the
P. minor
,
but also the other weeds like
L.
temulentum, A. ludoviciana, Malva
sp.
etc.
have entered from traditional wheat growing
areas to non-traditional wheat growing areas
including West Bengal through supplied food
grains. In wheat, seed rate being 100-120 kg
ha-1, an admixture of weed seeds to the level
of 1% as sometimes recommended for certified
seeds, will put exactly 1.0-1.2 kg weed seed
in one hectare. Ideally this should be ‘0’ for all
weeds, as quality of crop seed at the time of
sowing is a parameter that can be readily
controlled. Although a figure of 1-3 seed(s)
sqm.-1 may seem insignificant, it is important
to control the level of weed introduction at
seeding time through efficient seed cleaning
procedures. This is especially so if the
introduced seed is herbicide-resistant. Weed
seed infestation in crop seed is an important
parameter with respect to the introduction of
weed seeds that may well be multiple or cross-
herbicide resistant. Even extremely low levels
of weed seed contamination are significant
due to resistance mechanisms of weeds.
In India,
P. minor
contamination to the
tune of 2-3 g kg-1 of wheat has been observed
in some wheat seeds commercially available
in the market for household consumption (Das,
2008). Farmers should use genetically pure
crop seeds and other propagating materials
free from weed seeds. Some weed species
which have been designated as objectionable
weed (a noxious weed whose seed separation
is difficult once mixed with crop seeds) under
the Indian Seed Act, 1966 and their maximum
permissible limits and the permissible limits
of total (composite) weed seeds in foundation
and certified seeds of crops have been assigned
(Table 1). Crop seeds like maize, cotton,
soybean, groundnut and pea having bigger size
are less prone for contamination / admixture
with weed seeds which are usually very small
in size, while crops like pearl millet, mustard,
lentil, sesame and forage crops on account of
their small seed size are more vulnerable to
have admixture with weed seeds (Table 2).
Higher the weightage given to a crop in the
Score Card, the greater is the chance of
admixture of weed seeds with that crop and
vice versa
.
SATSA Mukhapatra - Annual Technical Issue 18 : 2014
52
Crops
Objectionable weeds
Permissible we
ed seed admixture limits
Objectionable weeds
(No. kg-1)
Total weeds
(No. kg-1)
Foundation
seed
Certified
seed
Foundation
seed
Certified
seed
Rice
Wild rice / red rice
(
Oryza sativa
var.
fatua
)
2
5 or
0.01%
10
20 or
0.1%
Wheat
Field bind weed
(
Convolvulus arvensis
) /
littleseed canary grass
(
Phalaris minor
)
2
5 or
0.01%
10
20 or
0.1%
Oat Wild oat (
Avena fatua
/
A. ludoviciana
)
2 5 10 20
Maize
-
None
None
None
None
Sorghum
-
-
-
5
10
Black gram
-
-
-
5
-
Green gram
-
-
-
-
10
Chickpea
-
-
-
None
None
Grass pea
-
-
-
5
10
Lentil
-
-
-
10
20
Mustard
Mexican poppy
(
Argemone mexicana
)
5
10 or
0.1%
10
20 or
0.5%
Soybean
-
-
-
5
10
Sunflower
Wild sunflower
None
None
5
10
Linseed
-
-
-
5
10
Niger
-
-
-
10
20
Safflower
Wild safflower
None
None
5
10
Sesame
-
-
-
10
20
Cotton
-
-
-
5
10
Jute
-
-
-
10
20
Berseem Chicory
(
Chicorium intybus
)
5 10 or
0.05%
10 20 or
0.5%
Lucerne Dodder (
Cuscuta
spp
.
) 5 10 or
0.05%
10 20 or
0.5%
Fenugreek
Melilotus alba
2 5 or
0.01%
10 20 or
0.2%
Lettuce
Lactuca serriola
2 5 or
0.01%
10 20 or
0.2%
Cucurbit
Cucurbita
spp.
None
None
None
None
Amaranth
Wild amaranth
5
10
10
20
Table 1. Crops and their associated objectionable and total weed seeds along with
their maximum permissible limits in foundation and certified seeds of cropsa
aModified after Jaya Kumar and Jagannathan (2003) and Das (2008)
SATSA Mukhapatra - Annual Technical Issue 18 : 2014
53
Table 2. Weightage to weed seed contamination allotted in Score Card for judging
quality of some crop seedsb
Crops Marks (%) Crops Marks (%)
Barley 35 Forage legumes 55
Wheta 35 Forage grasses 45
Oat 35 Cowpea 30
Sorghum 25 Soybean 10
Cotton 0Potato 0
Maize 0Linseed 12
bModified after Dungan and Bolin (1950) and Das (2008)
Preventing introduction through
movement of machinery and farm animals :
Movement of unclean equipment or
machinery from a noxious weed-contaminated
area to a non-contaminated area should be
restricted. The farm machineries like tillage
and harvest implements are another source
which weed seeds get into crop field. They
should be cleaned properly and the soil sticking
to the implements particularly ploughs and
tractors must be removed before it is carried
to another field. Several weed seeds entangle
/ adhere with the furs and skin of animals by
means of some hook-like structure and
dispersed. So, similar precautions should be
taken. Though these are very small efforts towards
weed prevention but have significant impact.
Well decomposed farm yard manure /
compost :
One of the main sources of adding weed
seeds in soil is the undecomposed farm yard
manure (FYM). Always well decomposed /
rotten manure free from weed seeds should
be used for seed production. However, a well
decomposed FYM may contain viable weed
seeds at various stages of decomposition. The
cattle and other livestock cannot completely
digest the weed seeds and pass viable weed
seeds along with their dung / litter. As the
importance of organic farming and organic
seed production is being increased day by day,
the use of organic matter and the fermentation
process needs to be improved or other superior
methods of composting should be explored.
Even after vermicompost of
Parthenium
the
viable seeds have been noticed when used in
crop field (Sarkar, 2014). Again the growth
and reproduction of various weeds to different
levels and sources of organic matter in the
context of organic seed production should be
critically examined.
SATSA Mukhapatra - Annual Technical Issue 18 : 2014
54
Clean irrigation channels :
The farmers many a time ignore to keep
the surroundings of the crop field clean specially
irrigation channels, bunds, roadsides, fences
and other areas, which are important sources
of entry of weed seeds or propagules into main
field. The seeds are carried with irrigation
water to the crop field. Weeds of those areas
should be controlled occasionally before
flowering to prevent seed formation and
perpetuation.
Weed control in nurseries :
One important mechanism of weed spread
is from the nursery to mainland with
transplanted seedlings. Appropriate weed
control measures should be adopted in the
nurseries of rice and vegetables. This assumes
greater importance for weeds like
E. crusgalli,
E. glabrescens
and other grassy weeds in rice.
Plant / weed quarantine :
Many regions of the country have flora
that contain a high proportion of introduced
species. Some of them become aggressive
weeds in their new surroundings and succeed
rapidly in invading particular habitat and
replacing indigenous species. The weed
problems will likely to increase due to increased
emphasis on high input agriculture.
Globalization may bring new weed problems
while importing or exporting agricultural
commodities as per the WTO agreement. The
most aggressive invasive weed species are
Chromolaena odorata, Lantana camara,
Mimosa
sp. and
Mikania micrantha
in forest
and grasslands;
Parthenium hysterophorus
in
non-cropped situations;
Eichhornia crassipes
in water bodies; and
P. minor
and
Avena fatua
in cropped areas. In addition to this, a number
of weeds have been found to be highly invasive
in arable agriculture. These species have
entered India either accidentally or deliberately
and have posed serious threat to environment,
agriculture and health of human and animal.
The first line of defense against weeds,
especially invasive species, is prevention, which
by and large depends on legislation backed
up inspection procedures. But, unfortunately,
this has not been put into real practice in our
country. A regulation is always required to
check both inter-state and inter-country
movement of weeds, especially noxious and
pernicious weeds with enforcement of laws.
So far, weed law exists only in Karnataka in
India, which declared
Parthenium
hysterophorus
as a noxious weed. It should be
strictly enacted across the states and countries.
Weed quarantine law enforces isolation of an
area where a serious weed has established
and prevents further movement of weeds into
non-infested area. Plant Quarantine Order
issued in 2003 imposes regulation on the
import of plants, plant products, soil, earth,
clay, compost, sand, peat etc. Consignment
of plants or plant products such as seeds of
cereals, pulses, oilseeds, fodder etc. will not
be permitted for import if found infested with
noxious weeds.
The import of wheat in India for
consumption purpose is regulated from the
SATSA Mukhapatra - Annual Technical Issue 18 : 2014
55
phytosanitory point of view under Plant
Quarantine (Regulation of import into India)
Order, 2003. According to the phytosanitary
regulation of this order, import of wheat
should be free from quarantine weeds listed
in Schedule VII of this order. Consequent upon
the policy decision taken by the Government
of India, about 6.2 million tons of wheat was
imported during 2006-07 by the Ministry of
Food (Anon., 2010). The import was mainly
for PDS from various countries such as
Australia, Russia, Canada, Ukraine, Hungary,
France, Kazakhstan, Romania, Bulgaria,
Netherlands and Argentina. The wheat was
imported through seaports of Chennai,
Cochin, Tuticorin, Mumbai, Visakhapatnam,
Kakinada, Kandla, Mundra and Mangalore.
These entry points are located either in the
non-wheat growing areas or non-traditional
wheat growing areas. Further, imported
wheat had been distributed by the Food
Corporation of India and private traders
through rail wagons and truck to the various
parts of the country.
According to the relaxed phytosanitory
condition for the import of wheat following the
Department of Agriculture and Cooperation
(DAC)’s Order, 2006, the wheat consignment
would require to certify to contain less than
average 100 quarantine weed seeds in 200 kg
of samples drawn as per the prescribed
procedure. Consequent upon the relaxation of
phytosanitory specification, many countries
were able to export wheat grains to India
meeting the relaxed phytosanitory conditions.
During the import of huge quantity of wheat,
large numbers of quarantine weed seeds were
intercepted by the plant quarantine officers at
the time of inspection of the consignments
(Table 3 and 4). Out of large number of weed
seeds, five have been assessed as important
with medium to high weed risk assessment
(WRA) value. The imported wheat seeds were
distributed in different districts of the country
through PDS. The seeds of these five invasive
weeds have spread throughout the country with
the distributed wheat seed. It is expected that
in the subsequent years they will germinate and
spread throughout the country.
Table 3. Number of quarantine weed seeds intercepted through imported wheat from various
countries
Source: Anon. (2010)
Weed intercepted
Country
of export
Quantity of
consignm ent (t)
No. of weed seeds intercepted
(sample size of wheat)
Cenchrus tribuloides
Australia 1,00,000 30 (575 kg)
Solanum carolinense
Australia 1,00,000 33 berries, each contain ing an
average of 25 see ds (525 kg
Viola arvensis
Russia 2,00,000 101 (200 kg)
Cynoglossum officinale
Russia 2,00,000 1 (200 kg)
Ambrosia trifida
Russia 46,000 9 (224 kg)
)
SATSA Mukhapatra - Annual Technical Issue 18 : 2014
56
Table 4. Total quantity of quarantine weed seeds intercepted through imported wheat
Weed intercepte d Weight (g) of
weed seeds (per
100 seeds)
Quantity of weed
seeds estimated
the consignm ent (kg)
Cenchrus tribulodies
3.1 165
Solanum carolinense
0.44 693
Viola arvensis
0.06 184
Cynoglossum officinale
- -
Ambrosia trifida
2.88 0.05
Source: Anon. (2010)
Unrestricted distribution of whole wheat
grains for human consumption throughout ten
states of country including West Bengal with
multiple rural outlets may pose serious threat
to the wheat growing areas. In West Bengal,
the wheat was distributed in all the districts
through PDS.
Majority of quarantine weed seeds
intercepted through imported wheat
consignment (even within the permissible limit)
have the capacity of germination in non-wheat
growing areas also and further spread to wheat
growing areas through air, water, transport,
planting materials, etc. Thus, these weeds not
only pose serious threat to Indian agriculture
in terms of affecting agricultural production
in wheat as well as other crops, but may also
pose serious health problems as evidenced in
case of introduction of
Parthenium
weed seeds
along with imported wheat from USA. Out of
these weeds,
Solanum carolinense
has already
been reported to spread in some of the
southern states like Tamil Nadu, Karnataka
etc.
Conclusion :
Weed is a part of each and every agro-
phytocoenosis. It will continue to remain so.
Further, the weed problem is likely to be
aggravated with changing perspective of
climate change, globalization and changes in
crop production technologies. Substantial
losses in quantity as well as quality of crop
seeds occur due to weed infestation.
‘Prevention is better than cure’ is very much
true for weed management point of view,
especially for quality seed production. Existing
quarantine system in India must be
strengthened. Strict quarantine law must be
enforced to check the entry of new weeds,
because many noxious weeds of other
countries are not yet reported in India but
those have the potentiality to grow in our
country.
SATSA Mukhapatra - Annual Technical Issue 18 : 2014
57
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pp. 19-30.
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901 pp.
Duary, B. and Mukherjee, A. 2013.
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