Weed Control and Issues in
Developing Countries
Peter R Hobbs
609 Bradfield
Department Crops and Soil Science
Challenge for Agriculture
• To increase food production sustainably to
meet food security needs of a growing
population now and in the future while at
the same time minimizing the effects on
the environment and improving the
livelihoods of those involved in agriculture
• Improve the efficiency of natural resource
use needed for agriculture
Convergence
of opinions
• Demand for food - increasing
• Harvested area - possibly shrinking
• Traditional sources of productivity growth
– are they exhausted?
• More competition for blue water
• More severe weather as a result of GHG
emissions and global climate change
• In addition, there is resource and
environmental degradation?
Resource Poor Farmers?
Subsistence Farmers?
• Not produce enough food to feed their
family or market any excess. Nutritional
quality of food produced can also be poor.
• Lack basic infra-structure to transport,
store and sell the food they grow
• Lack income and access to credit to invest
in new technology
• Little capacity to manage risks associated
with technology
South Asia
Pakistan
Nepal
IGP
Bangladesh
India
Indo-Gangetic Plains
• The population of South Asia is over 1.5
billion and increased at 1.8% per year over
last 6 years. 27.3 million more mouths to
feed each year!! 75K/day; 3,116/hr
– (IRAQ = 23 million; NY + Mass = 25m;
• More than 400 million are poor (< $1/day)
• The per capita rice-wheat growing areas
have shrunk from 1200 m2 in 1961 to less
than 700 m2 in 2000.
• Demand for rice and wheat will grow at 2.5%
per year in the next 20 years. This has to
come from yield growth.
Source: Indian Census Report
Population Dynamics
Rice plus wheat area per capita
1400
1200
1000
meter square
R+W
800
Rice
600
400
Wheat
200
19611971198119912001
Census years
Compound rates of decrease for decade shown as a % per year for rice+wheat area
Population density in RW area
of Indo-Gangetic Plains
RW area population = 280 million
RW area pop density = 517 /sq km
Green area population = 430 million
Green area pop density = 452 /sq km
Source: Dave Hodson, GIS Lab, CIMMYT
RW zone
Mid-hills North
Transition South
Rice-wheat systems in South Asia
• Rice and wheat grown in the same
calendar year in S. Asia (13.5 m ha’s)
– Rice in the wet monsoon summer and wheat
in the dry cool winter
– Rice grown by puddling soil and transplanting
seedlings
– This creates a problem for the next wheat
crop because of poor soil physical properties
– This also affects soil biology
R-W Systems Calendar
Summer
Month
Winter
J F M A M J J A S O N D J F M A
Wheat
Wheat
Rice
Rice-1
Wheat
Wheat
Rice-2
Rice
GM
Wheat
Rice
Wheat
NR
Wheat
Wheat
There are also rotations of RW with Sugarcane
NR = potato, vegetable, legume, oilseed
Phalaris minor issue
• This WAS a major problem in NW India
and Pakistan in wheat in the 1990’s.
• Herbicide resistant Phalaris to Isoproturon
started show in early 1990’s
• It became a major problem by mid-1990’s
• Need for integrated weed management
approaches –
– rotations, tillage, seed, variety etc.
Promote Integrated Weed
Management Systems
•
•
•
•
•
•
•
•
Hand weeding
Rotations – use of a fodder crop
Inter-cultivation
Mulching – allelopathic properties of some
residues and cover crops
Prevent seed set of weeds
Clean seed
Use herbicides when needed in proper manner
Etc.
Crisis in Haryana (and Punjab, UP)
• Herbicide tolerant Phalaris minor
seen as early as 1992-93 wheat
season
• Crisis level reached by 1995-96
• In affected fields, Phalaris
populations up to 3000 plants/ m3
– wheat crop squeezed out
Photo: LW Harrington
• Problem spreading fast into
neighboring states
Phalaris minor
(little seeded canarygrass)
A desperate search for solutions
• Improved management - crop
rotations, timely sowing, clean
seed, etc. of limited help
• New herbicides
• Zero tillage (?)
• Major role played by R.K.
Malik, Haryana Agricultural
University
Photo: LW Harrington
1800
1800
1600
1600
1400
1400
1200
1200
1000
1000
800
800
600
600
400
400
200
200
0
0
5800
5800
5600
5600
5400
5400
5200
5200
5000
5000
4800
4800
4600
4600
ZTPOP
ZTPOP
CTPOP
CTPOP
ZTYIELD
ZTYIELD
CTYIELD
CTYIELD
1997-98
1997-98
1998-99
1998-99
1999-2K
1999-2K
Year
Year
2000-01
2000-01
2001-02
2001-02
Grain
GrainYield
Yield(kq/ha)
(kq/ha)
Phalaris
Phalarispopulation
population(no/m
(no/m2) 2)
Grain yield of wheat and population of Phalaris under zero and conventional tillage.
Another pleasant surprise
• It took the Phalaris crisis for
farmers to try no-till
• Result of farmer trials – huge
enthusiasm for cost reduction
• Increasing number of projects,
farmer trials
• Traveling seminars helped
promote awareness in1998
• Private sector kept improving
implements
Photo: LW Harrington
Means and ends keep changing!
• No till originally seen as a
means of advancing sowing
dates
• Breakthrough with farmers
came with no-till as a means of
helping control Phalaris minor
• Essential local manufacturers
were involved and linked to
farmers
• Continued farmer interest in
no-till as a means of reducing
costs
Photo: LW Harrington
New Herbicides
•
•
•
•
Topik -- Clodinafop
Puma -- Fenoxyprop
Leader – Sulfosulfuron -- Sulfonylurea
Grasp -- Tralkoxydim
• Need to be applied with a sprayer – low
quantities active ingredient used per
hectare used (10-50 grams/ha)
No-Tillage with Inverted-T
• Based on inverted-T
coulter from NZ
• Good where no loose
residues including
anchored straw
• Locally made and low
cost
• Can adapt present farmer
machinery
• Uses 15-25% less water
• Less weeds germinate
• Service providers means
small farmers can use
No-Till
Conventional
Phalaris population over time
2500
b
2000
Phalaris population
b
1500
a
1
96-97
97-98
a
b
1000
a
500
0
NT
CT
Tillage s ys te m
98-99
Herbicide Application Using
Knapsack Sprayers essential
A. Miller and R. Bellinder, Cornell University,
in cooperation with Dr. R.K. Malik (HAU), Dr. L.S. Brar
(PAU) G. Singh (GBPUAT Pantnagar) J. Ranjit (NARC)
and Dr. P. Hobbs (CIMMYT)
Resource poor farmer systems for
herbicide application
Los Banos, Philippines. Puddling rice soils with carabao
Rice planting methods
Weeding in Rice
Taiwan
Girls weeding rice
No-till rice-wheat
• In order to get the full benefit of no-till
wheat, also need to no-till rice
– Problems of weeds because difficult to pond
water when no puddling
– Traditionally hand weeded
– Tedious and usually done by women
• One solution would be to introduce
herbicide resistant rice varieties
• Use of cover crops
Other Future Issues Rice
• Better 0-till and DSR varieties
– Oryza sativa by O. glaberimma crosses
– Chromosome substitution lines
• Use of Genetic Engineering
– Roundup ready rice
– Blast resistant rice
– Drought tolerant rice
• Improved equipment for seeding rice
Herbicide Tolerant (HT) Rice
Weed Control: Mechanical, Herbicides
Herbicides:
Broad Spectrum – ie. Glyphosate, Glufosinate
Narrow Spectrum – ie. 2,4 - D
LD50 = 4320 mg/kg
DDT = 115
Parathion = 30
Bt = >5000
Herbicide Tolerant (HT) Crops
•
•
Gene Source: various bacteria
How does it work:
1. Insert gene for herbicide de-toxification
2. Replace herbicide target with gene that is
resistant to herbicide
Benefit of HT to Environment?
• Depends on Herbicide not GM Plant
• Post emergence broad spectrum Roundup
herbicide replace numerous narrow
spectrum herbicides that are more toxic
– Depends on breakdown product of herbicide
in plant/soil
• Allows farmer to practice no-till and
conservation agriculture practices
Negative issues
• Weeds used for fodder
• Employment of the poor for weeding
• Availability of technology to resource poor
farmers:
– Credit to buy sprayer and herbicide
– Training in proper use
– Spurious products on the market
– Extension of improved system poor
Maize in Zambia -- Traditional
Zambia – Basin System
Conservation Agriculture
Residue retention distinguishes
Conservation Agriculture from
conventional farming systems,
which are characterized by leaving
the soil bare and unprotected,
exposed to climatic agents.
The soil cover is not incorporated
into the soil by tillage.
(FAO, 2002)