3rd Africa Rice Congress Theme 2: Intensification and diversification Mini symposium: Enhancing productivity through improved water and weed management Author: Rodenburg

1. Labor-saving Weed Management Tools for Lowland Rice:
Comparing the Use of a Pre-emergence
Herbicide, Rotary Weeders and Hand Weeding
Jonne Rodenburg
Kazuki Saito
Runyambo Irakiza
Derek W. Makokha
Kalimuthu Senthilkumar
Africa Rice Center

2. Introduction
• Weeds: important yield reducing factor in
rice in sub-Saharan Africa (SSA)
• Total annual production losses: 2.2 Mt
• Annual economic impact: 1.5 billion USD
• Hand weeding: 30-70% (250–780 man hour
ha-1) of total labor demand
• Weeding 1 ha: walking 10 km head down
• Labor-saving weed management technologies
are a necessity
• Rotary weeders and herbicides
• Time gains never comparatively quantified

3. Materials & Methods
•
•
•
•
Bagamoyo, Tanzania
RCBD, 4 replicates, 2 seasons
Plot size: 6
8 m
Treatments:
1. Hand weeding at 21, 42 DAT
2. Straight spike floating weeder
(A) at 21, 42 DAT
A
3. Twisted spike floating weeder
(B) at 21, 42 DAT
4. Pre-emergence herbicide
(Oxadiazon: Ronstar) at 4 DAT,
hand weeding at 42 DAT
• Rotary weeding between rows
followed by hand weeding in rows
• Data: Weed management time, weed
biomass and rice yields
B

4. Results
Twisted-spike weeder
2012
Straight-spike weeder
2013
PE herbicide
Hand weeding
0
100
200
Time (seconds m-2 person-1)
• Significant
(P<0.001) time
reductions
observed with the
rotary weeders
and herbicide
application
compared to hand
weeding
Time savings compared
to hand weeding (%)
2012
2013
Twisted-spike weeder
40
56
Straight-spike weeder
32
49
PE herbicide
88
97
• Time savings: 3256% (weeders),8897% (herbicide)

5. Results
2012, 21 DAT
Twisted-spike weeder
2012, 42 DAT
Straight-spike weeder
2013, 21 DAT
PE herbicide
2013, 42 DAT
Hand weeding
• Weed biomass dw:
o lower (P<0.05) in PE
herbicide plots at
21 (both years) and
42 DAT (2013)
0
6
12
18
Weed dry weight (g m-2)
• Rice grain yields:
Twisted-spike weeder
2012
o 2012: no differences
Straight-spike weeder
2013
o 2013 > 2012
PE herbicide
Hand weeding
0
5
Yield (t ha-1)
10
o 2013: PE herbicide
significant (P<0.05)
higher than any
other treatment

6. Discussion
• Significant time savings with PE herbicide
and rotary weeders on 48 m2 plots
o implications for larger areas still unknown
• Herbicide application:
o yield and weed control advantage
o knowledge intensive, market
dependent, expensive; health/environmental
risks
• Rotary weeders:
o no yield or weed control advantage,
availability of weeders, row
planting, manpower
requires
o relatively cheap and easy, compatible with
IWM, GAP

7. Conclusions
• Correct use of herbicides can reduce
farmers’ time for weed management
• Rotary weeders: more time- and manpowerdemanding than herbicides, but reduce
weeding time by at least a third compared
to hand weeding
• Differences between weeders, hence they
should be locally adapted
• In the long run rotary weeders are more
cost-effective, environmentally benign
than herbicides
• Suitable component technology for
resource-poor rice farmers in SSA

8. Way forward
• Agronomy
o studying yield advantages, long-term effects
o participatory on-farm rotary weeder tests in
11 countries
• Mechanization
o local adjustments
o motorized rotary weeder
o (more) blacksmith training workshops
• Social science
o impact on gender relations
• Economics
o economic analyses of weed management options
• Phytopathology
o effects of on disease spread

9. DVD
Farmer-to-Farmer Instruction Videos
on Effective and Labor-Saving Weed
Management in Lowland Rice
• 4 multi-language videos:
o Effective weed management
o Rice transplanting
o Safe and correct use of herbicides
o Using the rotary weeder in lowland
rice
• Technical drawings of rotary weeders and
line-makers
• Farmer training modules on Integrated
Rice Management (PLAR-IRM)
Copies available at the AfricaRice booth (this conference)

10. Thank you - Merci - Na som djita
Hartelijk dank
-ご静聴ありがとうございました