Labor-saving Weed Management Tools for Lowland Rice: Comparing the Use of a Pre-emergence Herbicide, Rotary Weeders and Hand Weeding

Jonne RodenburgKazuki Saito

Runyambo IrakizaDerek W. Makokha

Kalimuthu Senthilkumar

Africa Rice Center

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

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

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

A

B

Results

Time savings

compared to hand

weeding (%)

2012 2013

Twisted-spike weeder 40 56

Straight-spike weeder 32 49

PE herbicide 88 97

• Significant (P<0.001) time reductions observed with the rotary weeders and herbicide application compared to hand weeding

• Time savings: 32-56% (weeders),88-97% (herbicide)

Hand weeding

PE herbicide

Straight-spike weeder

Twisted-spike weeder

0 40 80 120

160

200

2012

2013

Time (seconds m-2 person-1)

Hand weeding

PE herbicide

Straight-spike weeder

Twisted-spike weeder

0 1 2 3 4 5 6 7 8

2012

2013

Yield (t ha-1)

Hand weeding

PE herbicide

Straight-spike weeder

Twisted-spike weeder

0 6 12 18

2012, 21 DAT

2012, 42 DAT

2013, 21 DAT

2013, 42 DAT

Weed dry weight (g m-2)

Results

• Weed biomass dw: o lower (P<0.05) in

PE herbicide plots at 21 (both years) and 42 DAT (2013)

• Rice grain yields: o 2012: no

differenceso 2013 > 2012o 2013: PE herbicide

significant (P<0.05) higher than any other treatment

Discussion

• Significant time savings with PE herbicide and rotary weeders on 48 m2 plotso 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, requires availability of weeders, row planting, manpower

o relatively cheap and easy, compatible with IWM, GAP

Conclusions• Correct use of herbicides can reduce

farmers’ time for weed management• Rotary weeders: more time- and

manpower-demanding 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

Way forward

• Agronomy o studying yield advantages, long-term effects

o participatory on-farm rotary weeder tests in 11 countries

• Mechanizationo local adjustmentso motorized rotary weeder o (more) blacksmith training workshops

• Social scienceo impact on gender relations

• Economicso economic analyses of weed management options

• Phytopathologyo effects of on disease spread

DVDFarmer-to-Farmer Instruction Videos on Effective and Labor-

Saving Weed Management in Lowland Rice

• 4 multi-language videos: o Effective weed managemento Rice transplantingo 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)

Thank you - Merci - Na som djita 

Hartelijk dank

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