Importance of Pesticides for Growing Rice in Sub-Saharan Africa Leonard P
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International Pesticide Benefit Case Study 101 July, 2014 Importance of Pesticides for Growing Rice in Sub-Saharan Africa Leonard P. Gianessi ice is the most rapidly growing food commodity in Sub-Saharan Africa. Traditionally, rice was grown as a subsistence crop by R smallholders and largely consumed on the farm. In recent years, demand from urban consumers for rice as a storable and easily prepared food has increased tremendously. Greater use of pesticides on farms in Sub-Saharan Africa has great potential for increasing rice production. INTRODUCTION Portions of the grain head are white in contrast to the In Sub-Saharan Africa (SSA) total rice consumption over green or tan color of healthy grain. This “blasted” the period 2000-2012 increased from 12MT to 24MT. appearance is caused by sterile or blank grain. In SSA, a African rice production has not been able to keep up blast disease outbreak can cause the loss of about 35- with demand and nearly 37% of the rice consumed in 50% of rice yield, and in serious outbreaks, 100% rice 2 SSA is imported at a cost of US$5 billion per year yield losses have been recorded. Rice farmers have draining foreign currency reserves. This reliance on food abandoned imports is a very risky, expensive and unsustainable some inland strategy and it may lead to severe food insecurity and valleys in civil instability.1 The risks became clear in 2008 during SSA because food riots in major African capitals in protest against of high blast 3 high rice prices caused by rice-exporting countries pressure. banning exports. Many African countries have Recent embarked on ambitious programs to boost their rice increases in production capacity.1 rice blast Rice Blast on Leaves. epidemics in SSA are associated with changes in climate A recent assessment by AfricaRice concluded that the and with increased use of fertilizers. In demonstration highest impact in benefitting rice production in SSA plots, the incidence of blast in plots without fertilizer would be provided by research addressing weed was one-seventh to one-half of that in plots that infestations followed by research addressing rice received fertilizer.4 Thus, blast constitutes a serious diseases.1 Research on insect control ranked 6th among constraint to intensification as a great part of the the research priorities, following research on soils benefit due to fertilizer application is lost by the (fertility), birds and rodents, and climate-related increase of the damage due to the disease.4 constraints (drought). Evaluations of fungicides in SSA for control of rice blast FUNGICIDES have been ongoing since the 1970s.The research has Farmers in SSA perceive rice diseases to be of high shown that under high blast pressure, application of importance with 21% identifying rice blast as a major fungicides at the right time results in significant yield constraint on production.1 Blast spores are present increases. Recent research in a blast-conducive year-round and can infect the rice plant at any growth environment in Burkina Faso resulted in rice yield stage. Foliar lesions reduce the leaf area available for increases of 44-124% following the application of a 4 photosynthesis. Blast stops nutrients and water from single fungicide treatment. The AfricaRice Center in a getting to the kernels, stopping kernel development. Production Handbook for Nigeria recommends fungicide 1 sprays on rice in areas conducive to fungal diseases.5 In point, where they feed while secreting a substance that Kenya, these fungicides are readily available in the inhibits the formation of panicles. Affected tillers do not market.2 In 2009, when Kenya was highly affected by produce a single grain of rice. Heavily infested fields blast, the government provided some of these may produce no grain at all. Studies over a five year fungicides to farmers for free.2 period with insecticides revealed that controlling the African rice gall midge prevented yield losses of 19, 17, INSECTICIDES 11, 11, and 3%.9 Insect pests substantially reduce rice yields in SSA. The estimates of rice yield loss due to insects in Africa range HERBICIDES 1 between 10% and 15%. The damage differs regionally According to surveys, African farmers see weeds as the by country and rice variety and in some years may most serious problem in rice production with 70% of 1 exceed 90%. African rice farmers identify the African farmers identifying weeds as a major constraint.1 (Every rice gall single rice farmer identified weeds as a problem). midge as a When weeds are not controlled, rice yield losses up to major 100% occur. Many rice fields have been abandoned due problem on to heavy weed infestation. 30% of their farms while Hand weeding is the traditional method of weed control stem borers on rice farms in SSA; this is labor demanding and 10 are a major requires about 125-172 hours/hectare per weeding. problem on Whiteheads caused by stem borers Two weedings by hand within 14-40 days after planting 19% of the farms.1 Tunneling of stem borer larvae have been recommended. Weeding is frequently severs tillers thus reducing their number through the inadequate or delayed, often due to labor shortages or 11 formation of “deadhearts.” Damaged shoots do not conflicts for time between on- and off- farm activities. produce a panicle and thus produce no grain.6 Feeding Farmers usually weed the rice crop at least once, of stem borers during the reproductive stage causes a though this is often delayed. Research has shown that severing of the developing panicle at its base. As a yields from farmer-weeded plots were significantly less result, the panicle is unfilled and whitish in color; rather (41%) than researcher-weeded plots. than filled with grain and is known as “whitehead.” A In a survey of rice farmers in Cote d’Ivoire, 53% of single insecticide spray based on thresholds of farmers reported that their rice fields were not always deadhearts or whiteheads resulted in yield increases of weeded.12 A reason given for this by almost two-thirds 10-18% and a cost benefit ratio of 1:17.4.7, 8 of the farmers was that weed infestation may be so The African rice gall midge has become more common severe that weeding was not always worthwhile, since the 1970s with outbreaks associated with rice-rice therefore the field would be effectively abandoned. double cropping and increases in fertilizer applications. Almost 80% of farmers said that if weeds were less of a The African rice gall midge looks like a mosquito. problem, they would increase the area of land under 12 Fertilized females can lay up to 300 eggs. When the rice cultivation. Uncontrolled weeds in SSA rice fields eggs hatch, the larvae migrate to the plant’s growing account for yield losses estimated at 2.2 million tons per year.11 2 Research with recommended herbicides in comparison Box 1: Herbicide success in Ghana to farmer weed control practices in Senegal and “For improving rice production in Ghana, the Ministry of Mauritania resulted in rice yield increase of .9-1.0 Food and Agriculture (MOFA) has made six key t/ha.13 The value of the increased production was 4.4 recommendations including the use of herbicides for times the cost of the herbicide treatments. With weed control. A 2012 survey in Ghana revealed high herbicide applications, the cost of weed control in rice herbicide use with 84% of rice area treated. The yield of can be about 50% lower than with hand or hoe plots with herbicides is significantly higher than of plots weeding.14 Herbicide use reduces weeding time by 88- without herbicides. For irrigated plots with fertilizer and certified seed, there was a 3.1 ton/ha difference 97% in comparison to hand weeding.15 Since farming in between plots with and without herbicide. For lowland Africa is essentially limited by the availability of labor, rain-fed areas, the difference was 1.4 tons/ha and for rather than the availability of land, any reduction in the upland areas the difference was 2.2 tons/ha. Farmers labor required for weeding would free farmers to using herbicides in Ghana save 55% in comparison to the expand their cultivation and therefore grow more rice. cost of hand-weeding. The entry of inexpensive herbicides into Ghana has made it cheaper to purchase and use herbicides than to spend much time or hire labor for weeding. The diffusion of herbicides in Ghana is wide and farmers are learning about it from other farmers. Half of farmers report that they knew about herbicide use and its benefits from advice by or observing other farmers’ plots. 32% of farmers said they had received information about herbicides from MOFA, 18% received information on herbicide use from visits by African women handweeding a rice field. agents or researchers and 11% from projects by donors Weed scientists and botanists at CIRAD and AfricaRice or NGOs. The adoption of herbicides by rice farmers in developed an interactive on-line weed identification Ghana suggests that if a technology is beneficial, it can spread rapidly among farmers.”16 tool (AFROweeds) to assist in weed management in rice. WARDA and IFDC developed a curriculum for Integrated were used on none of the rice acres in two regions and Rice Management in inland valleys of SSA consisting of a 83-100% of the acres in four regions.14 A survey of 13 technical manual and a facilitator’s guide including a rice-growing regions in Nigeria revealed no use of module on the use of herbicides. The AfricaRice Center herbicides.17 Fungicide application is almost non- in a Production Handbook for Nigeria includes herbicide existent in the rice fields of the SSA.