Positive Developments in Integrated Pest Control for Cotton in West Africa

Dr. Ouola TRAORE, Agro-Soil Scientist, Senior Scientist Institute of the Environment and Agricultural Research (INERA), Cotton Program 01 BP 208 Bobo-Dioulasso 01, Burkina Faso E-mail: [email protected]

Introduction Cotton is one of the leading cash crops in the West African subregion. It employs more than 10 million growers. In 2007, total output came to 1.2 million metric tons on approximately 1.5 million hectares, for an average yield of 800 kg/ha. Lint exports from these countries account for less than 15 percent of world exports but are second highest worldwide, trailing the USA. Yields recorded significant growth of 6 percent annually between 1960 and 1980, versus 2 percent worldwide. Beginning in the 1980s, though, yields virtually stagnated, or even declined. This situation is due to a number of factors: - dismantling of the extension system; - declining soil fertility; - declining world prices for cotton lint; - difficulties with pest control: Cotton is one of the most highly attacked plants in the world. Hargreaves has recorded more than 1,300 insect and acarid species on cotton plants, and this does not include nematodes and mammals. In the absence of pest and disease control, average harvest losses in the West African subregion range between 40 and 70 percent, depending on the agro- ecological zone and the year. This paper reviews integrated pest control efforts undertaken in the West African cotton sector. According to the International Organization for Biological Control (IOBC), integrated control is “a system for controlling noxious organisms that uses a set of methods meeting economic, ecological, and toxicological requirements, with priority given to the deliberate implementation of natural limiting factors and respect for tolerance thresholds.” For the cotton plant, integrated pest control requires full knowledge of the plant’s main pests and diseases and their natural enemies. I. Cotton pests in West Africa Cauquil (1986) classifies cotton pests according to the types of organs attacked on the plant. All parts of the plant are attacked (seeds, roots, vegetative and fruit-bearing organs). The principal pests and diseases of the vegetative and fruit-bearing organs of the cotton plant can be divided into three groups, according to the phenological stage of the plant: 1. Principal seed and root pests 1.1. Principal seed pests Insects of the Tenebrionidae family (Tribolium castaneum) attack the seed during storage. The seed also harbors Pectinophora gossypiella and Cryptophlebia leucotreta caterpillars in areas where these pests proliferate. At sowing, the seed and the young plantlet are attacked by diplopods (millipedes). The most harmful species belong to the genera Peridontopyge and Tibiomus. These species are dark in color, with alternating lighter-colored bands and blackish- brown bands. Their cross-section is round, and they range from 2 to 8 cm in length. Diplopods attack and hollow out the seed. They feed on it during germination. 1.2. Principal root pests These primarily consist of insects and nematodes.
Insects Syagrus calcaratus: A small, shiny blue-black beetle with a tawny orange thorax and lower legs. The orange-headed adults feed on the leaves, in which they leave elongated perforations. The

-1- larvae live in the soil, where they feed on the roots, which they decorticate by making rings around these organs, leading to a characteristic wilting of the plant.
Nematodes Noxious nematodes belonging to the Nemathelminths have been identified in root ectoparasites and endoparasites. They fall mainly within the genera Pratylenchus, Rotylenchus, Meloidogyne, Scutellonema, and Helicotylenchus. 2. Principal leaf pests and their damage 2.1. Phyllophagous caterpillars
Syllepte derogata This is the cigarette-shape “leaf-rolling” caterpillar. It is light green in color, often translucent with a black head. It attacks leaves at all stages of the plant’s development by spinning silky threads. Black excrement can be seen inside the leaf. Infestations of this pest are often localized within the field and may result in spectacular defoliation. It also attacks okra.
Spodoptera littoralis The caterpillar may be brown, yellowish, or gray. It is characterized by two rows of black triangles on the back and a light line on each side. But these triangles may be present only at the front or rear of the body. The eggs are deposited in a pile on the underside of the leaves, where the young caterpillars are born and then begin to feed on the supporting leaves. Older caterpillars perforate the leaves and also attack the reproductive organs. Spodoptera also causes damage to cowpeas, groundnuts, etc.
Anomis flava This is the “surveyor caterpillar,” so called because of its highly characteristic motion. The caterpillar is yellow, with a yellow or greenish-yellow head. It has five, very fine white lines on its back. It attacks leaves only. Damage from these caterpillars consists of circular perforations measuring 1 to 3 cm in diameter in the leaves. 2.2. Phyllophagous beetles
Flea beetles These small, highly mobile insects are of several colors. They make lots of holes in the leaves of young glandless cotton plants. - Nisotra dilecta: blue - Nisotra uniformis: brown - Podagrica decolorata: yellow-orange They are also found on okra, the various Hibiscus (jutes, kenaf, etc.), and sometimes on glanded cotton plants. 2.3. Acarids There are two genera that are cotton pests in the subregion: Tetranychus or red spider mites and Tarsonemus mites, which are the most important. They are tiny, almost invisible to the naked eye, and live on the underside of the leaf.
Tetranychus All the species encountered belong to the genus Tetranychus. They include T. urticae, T. neocaledonicus, and T. falcaratus. They are red in color, hence the name of red spiders. They are not very mobile. They feed on the underside of leaves with a necrosed appearance. They are usually unimportant.
Tarsonemus The most important species is Polyphagotarsonemus latus, which is yellow-white in color and highly mobile. It appears on cotton plants in humid zones (rainfall above 1000 mm/year), especially Benin, Côte d’Ivoire, and Togo. It has a very short biological cycle, multiplies every five days, and causes substantial damage, particularly in damp, overcast conditions. Affected leaves show a number of successive symptoms, depending on the level of gravity: - the underside is dark green, glazed, oily, and shiny; - the sides of the limb roll downward; - the leaves look chapped and torn as if cut by a knife.

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The plant takes on a spindly appearance with few or no fruit-bearing organs. Early or severe attacks result in heavy declines in output. 2.4. Piercing and sucking insects These include the Homoptera and the Heteroptera. The former are the most dangerous. Among the Homoptera, aphids, white flies, and jassids are of concern, while the Heteroptera include, in particular, mirids (Dysdercus sp. and Helopeltis schoutedeni). 2.4.1. Homoptera
Aphids: Aphis gossypii These are yellow, yellow-green, or black-green in color, may be either winged or apterous, and have a very short biological cycle. They are polyphagous. They live in colonies on the underside of leaves that become arched and tense and shrivel downward. The waste matter, consisting of a sweet substance (honeydew), falls on the leaves and gives them a shiny appearance. Microorganisms (mushrooms) may develop on the honeydew and produce a black discoloration on the leaves and the seed cotton: this is called sooty mold.
White flies: Bemisia tabaci The larvae are oval in shape, flattened, and green when they are young but yellowish when they are older. They are attached to the underside of the leaves. The adults are very small insects with two pairs of white wings. They are very mobile and flit around the plant. Large populations cause the leaves to yellow and disturb the plant’s development. As in the case of aphids, they also produce a honeydew that soils the cotton in open capsules. This pest is also highly polyphagous: it can be found on many other cultivated plants, particularly market gardening crops such as tomatoes.
Jassids: Jacobiella fascialis These are tiny green insects with a characteristic, oblique type of motion. They pierce the leaves, which then take on a reddish appearance around the edges. 2.4.2. Heteroptera The genera and species that attack the cotton plant are very numerous in the subregion and particularly in the most humid zones. The main concern is:
Helopeltis schoutedeni This is a mirid with an elongated form and orange-yellow or bright red coloring. It is found mainly in the most humid zones. It attacks the leaves, branches, stems, and capsules and produces brown or black cankers. In the case of early and severe attacks, the leaves become waffled and cracked, taking on the appearance of “claws.” The plant’s growth is slowed as a result. Other Heteroptera of lesser economic importance also bear mention: Anoplocnomus curvipes, Campyloma spp., etc. 3. Principal reproductive organ pests These include both insects and mammals. 3.1. Insects These are classified as carpophagous insects with exocarpal and endocarpal diets. 3.1.1. Carpophagous insects with an exocarpal diet

Helicoverpa armigera The caterpillars are of variable color, with two light lateral lines and small hairs on the body. They attack and cause major damage to the flower buds, flowers, and capsules. The larvae are highly voracious. A single larva can destroy in one day between five and ten reproductive organs, specifically the squares, flower buds, and flowers. The excrement on flower buds and capsules that have been attacked is often abundant and expelled from the organ. In certain cases (second- generation infestation and shortage of the abovementioned organs), the caterpillar may attack young leaves and branches. H. armigera is highly polyphagous (cultivated plants: maize, sorghum, tomatoes, sunflowers, etc., as well as wild plants: Cleome viscosa, etc.).
Diparopsis watersi

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The young, yellowish caterpillar later becomes pale green and squat, with horizontal red lines that grow closer together toward the head. It reaches full growth at 2.5 to 3 cm in length. It is not very mobile and it attacks flower buds, flowers, and capsules by perforating them so that they sometimes remain hanging from the plant by threads. It is much less voracious than H. armigera. After nearly having disappeared from the West African subregion due to the introduction of pyrethroids in the late 1970s, this pest has reappeared at relatively high levels since the reintroduction of endosulfan. This active matter, designed to manage the resistance to pyrethroids acquired by H. armigera, is in fact very inadequate on Diparopsis.
Earias insulana and E. biplaga The squat caterpillars are easy to recognize because they have numerous spines, hence their popular name of “spiny” caterpillars. They attack the terminal buds (topping) and the flower buds, flowers, and capsules. The entry holes are quite large and easily visible. 3.1.2. Carpophagous insects with an endocarpal diet

Pectinophora gossypiella (pink bollworm) Called the pink bollworm because of its color, this caterpillar has segments marked with bands and horizontal lines. Fully grown, it reaches a length of 1 to 1.5 cm. It is sometimes confused with Cryptophlebia. It attacks the flowers and causes a specific symptom: “rosette flowers.” At birth, the caterpillar enters directly into the attacked organ and feeds by preference on capsule seeds, causing damage that is often followed by secondary rot. P. gossypiella lives solely on plants of the same family as cotton.
Cryptophlebia leucotreta The caterpillar is pale gray at full growth and resembles a pink bollworm. It has the same mode of attack and causes the same damage as P. gossypiella (deteriorated seed cotton, orange segment, etc.). The caterpillar’s entry hole into the capsule produces a curl. C. leucotreta is highly polyphagous and also attacks maize, guava, citrus fruit, etc. 3.1.3. Carpophagous Heteroptera

Dysdercus vöelkeri This is a large, red and black mirid, 1 to 1.5 cm in length. The larvae are apterous, while the adults have front wings characterized by two black dots centered on a light brown background and ending in a black band. They are all bright red in color and live in colonies. D. vöelkeri pierces green capsules or those that are already open in order to feed on the seeds. It depreciates the germinative value of the seed and the fiber which it discolors. 3.2. Mammals The arrival and spread of glandless cotton varieties in the mid 1980s caused mammals (particularly monkeys and rodents) to develop an interest in this plant and inflict damage of major economic importance. At the same time, the very high pressure on ophidians, particularly the family of Boidae (Phyton regius), exacerbated the phenomenon with a very high proliferation of rodents on glanded cotton varieties. These rodents belong to the following families, genera, and species: Muridae Mastomys natalensis Myomis dybowskii M. deroii Rattus rattus Arvicanthis niloticus Cricetomidae Cricetomys gambianus C. emini Sciuridae Funisciurus anerythrus F. leucogenys Xerus erythropus Gabillidae Tatera guinae T. kempii They attack all reproductive and sometimes the vegetative organs, which they then consume either within the cotton field or in the surrounding bush. The damage is sometimes very high and may cause growers to lose harvests. II. Principal cotton plant diseases and deficiencies in West Africa 1. Cotton plant diseases Cotton plants are attacked by certain diseases, often of minor importance but which can become major in the case of severe attacks. They include, in particular:
Bacteriosis: The new form that has developed is called “black arm.” All the aerial organs of the plant (leaves, branches, stems, capsules, etc.) are attacked from the beginning to the end of the

-4- cotton plant’s growth cycle. The foliar symptoms are angular, oily blotches, while cankers appear on the stems and rot on the capsules. In varying degrees, depending on location, bacteriosis has attacked virtually all the varieties grown in the subregion for nearly 15 years now.
Floral virescence: This disease leads to a yellowing of the leaves and stems, transformation of floral organs into foliated organs, a greening of the corolla and the stamens, and, finally, a proliferation of branches at the internodes, resulting in spectacular sterility. It is transmitted by an infectious agent akin to the Mycoplasma. The vector is a Homoptera, and the main species is Orosius cellulosus.
Blue disease: Plant growth is slowed down if the attack comes early. The internodes become shorter, the plant takes on a bush-like, sometimes creeping appearance, and the leaf blades become thicker and take on a bluish-green appearance, darker than normal and brittle in texture, with the edges rolled downward; the leaf blades themselves tend to become vertical. In the beginning, the flower-bearing organs are scrawny, and they cease to appear if the attack continues. But if the attack comes late, then the symptoms are confined to the vegetative extremities. 2. Mineral deficiencies and growth accidents
Potassium deficiency: This can be recognized by the presence of yellowish blotches between veins of the leaves, the edges of which turn brown. At an advanced stage, the leaves dry out completely but still hang on to the plant, looking rather like bats. The cotton lint yield and quality both diminish.
Growth accidents: Lightning strikes may cause damage of a natural origin in certain countries and locations. The affected area is always circular (roughly 12 meters in diameter), equivalent to the area covered by 15 ridges spaced 0.8 meters apart. The leaves of the affected cotton plants dry out and fall off the plant, leaving brown, seemingly burned stems. The damage is different from phytotoxicity. Damage from lightning strikes is sometimes wrongly confused with damage caused by insects. III. Principal components of integrated control in West Africa 1. Seed disinfection The seed is one of the most important inputs in the cotton production chain. It must be protected against all forms of aggression that could affect its quality. To achieve good sprouting, the seed must first of all have good germinative capacity. Unfortunately, cotton growers often run into problems of poor sprouting on their farms. The objective of seed disinfection is to preserve seed quality. The principal causes of poor sprouting are: - Abiotic factors: The seed handling and storage conditions must take into account any excessive heat or humidity in order to avoid seed deterioration. - Biotic factors: These include diseases and pests.

Diseases Damping off is by far the most important. This is caused by a complex of pathogenic mushrooms that are either agents carried by seeds (Colletotrichum gossypii, Fusarium spp) or agents found in the soil (Rhizoctonia solan, Pythium spp, Macrophomina phaseoli). Attacks may occur either before or after sprouting. If before, the seeds rot in the soil and do not germinate. By contrast, in the case of damage after sprouting, the seeds germinate but the young plantlets wither and soon die.
Seed and plantlet pests Many insects may cause non-germination or poor sprouting of the cotton seed. Some destroy the seed by consuming the kernel. Others attack the plantlets when they are in the cotyledonary stage. This latter category of seed and plantlet pests includes julids, which hollow out the seeds in the soil or gnaw on the cotyledons or the tigelle of the plantlets. Insects whose larvae live in the soil

-5- also attack the plantlets, typically the small roots (Syagrus, crickets, ants, aphids, and even some caterpillars). 1.3. Seed treatment To obtain good sprouting, the seed must first of all have good germinative capacity, but it must also be protected from attacks by diseases and pests. The principal insecticides and fungicides used in West Africa and their doses are shown in the following table: Table 1: Doses of the principal insecticides and fungicides used in West Africa Active substances Minimum dose Maximum dose (g/kg seed) (g/kg seed) Insecticides Benfuracarb 1 4 Carbosulfan 1.25 2.5 Imidacloprid 2.5 3.5 Thiamethoxam 0.15 1 Chlorpyriphos ethyl 0.5 4 Fungicides Carbendazime 0.7 4 Chlorothalonil 1 - Metalaxyl 0.35 1.6 Propiconazole 0.15 - TMTD - Thirame 0.75 3.2

2. Varietal control The method of varietal control encompasses all the qualities induced in the cotton plant, through traditional selection or modern biotechnology, for the purpose of reducing the impact of certain pests on seed cotton yields. These qualities may involve the production of excrescences on the organs of the cotton plant so as to prevent movements by pests (pilosity) or the production of toxins harmful to pests (VIP and Bt proteins).
A few examples of varietal control and their implementation - Glanded cotton plants Classic cotton plants contain phenolic yellow pigments called gossypol. This gossypol is present in small glands found in the various organs of the plant. The gossypol is used to fight against infestations of beetles that produce small holes in the leaves. The varieties without gossypol (i.e. glandless varieties) are useful for animal feed, through their seeds, but they are strongly attacked by beetles. That is the reason why this type of variety is not widely grown in the subregion. - Cotton plants with pilosity to combat jassids Jassids are small leafhoppers that move around on various organs of the cotton plant. They pierce and suck the sap, often transmitting diseases to cotton plants, as in the case of Orosius cellulosus which transmits a mycoplasmal disease called floral virescence or phyllody. The typical diagonal movement of jassids is greatly obstructed by the presence of pilosity on the organs of the cotton plant. This simple fact reduces the presence of this pest on the cotton plant; in such a case, the pest prefers to look for other plants where it can move around more easily. Today, the impact of jassids (O. cellulosus, which transmits phyllody to the cotton plant) is greatly controlled by the use of systemic seed treatment insecticides such as neonicotinoids (imidaclopride, thiamethoxam, acetamipride), carbamates (carbosulfan), etc. The use of pilose varieties is no longer in fashion, all the more so because infestations of the white fly Bemisia tabaci – a leading cotton plant pest in the subregion since the late 1990s – are greatly encouraged by this type of variety. In fact, the larvae of B. tabaci, once attached to the leaf,

-6- become inaccessible to their natural enemies and are only slightly reached by the insecticides used against them. Research on varietal selection in the subregion should now focus on hairless varieties that make access to B. tabaci larvae easier for natural enemies and insecticides. In Burkina Faso, for example, the FK37 variety has considerably less pilosity than FK290, which is being phased out. Researchers’ efforts to improve varieties in the West African subregion should continue in the same direction. - Genetically modified cotton (GMC) to combat capsule and leaf caterpillars A GMC is a conventional cotton plant that has received a gene enabling it to acquire an additional characteristic. The insertion or transgenesis can be accomplished by physical or biological methods. To protect the cotton plant against pests, the inserted genes come from Bacillus thuringiensis, which is a soil bacterium. The GMCs currently available are effective against most larvae of carpophagous and phyllophagous moths. The toxins produced by the GMCs have no direct effect on piercing and sucking Homoptera including aphids, white flies, and jassids. If necessary, treatments targeting these piercing and sucking insects are warranted. The fact of not using insecticides to control moth larvae encourages the presence of natural enemies. 3. Agronomic control Agronomic control of cotton plant pests includes the whole range of farming techniques used to disturb the development of pests at a given stage of their biological cycle. These techniques run all the way from preparing the field to performing post-harvest operations.
A few examples of agronomic control and their implementation - Early sowing to control second-generation H. armigera Conventional cotton growing depends greatly on the period when the crop is started. Early sowing is recommended in order to avoid rainfall cessation at the time of cotton plant fructification, which would cause a decline in productivity. In regard to phytosanitary protection, early sowing is also recommended, as soon as the rains have begun, to prevent the most sensitive period for the cotton plant from coinciding with second-generation H. armigera, which causes very serious damage at this phase. Two to three generations of H. armigera have been found on cotton plants, depending on the length of the rainy season. This pest’s first phase of proliferation takes place between mid- July and mid-August in the West African subregion and matches the development of the first fruit-bearing organs. Very often, this phase is not especially dangerous because the individual pests are few in number and are more highly sensitive to the insecticides. The second generation is observed between mid-September and mid-October. This is the most dangerous generation because the individuals resulting from parents that survived the first generation develop some tolerance of the insecticides, which makes them harder to control. - Plowing Deep plowing is a way to bring the chrysalises of pests to the surface before the butterflies emerge. These chrysalises are either gathered by birds or dried out by the climate, thus diminishing the number of butterflies to emerge. - Hoeing This operation serves to eliminate weeds in the vicinity of the cotton plant, and thus potential hosts for pests. A well aerated field receives better penetration of insecticide treatments in the various organs of the cotton plant. - Early and staggered harvests Insecticide applications cease several days before the start of the harvest. Piercing and sucking insects such as the aphid Aphis gossypii and the white fly Bemisia tabaci feed on the young buds and produce sweet substances that result in sticky cotton. To avoid this, it is recommended that growers harvest their crop as the capsules gradually open.

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- Destruction of old cotton plants to control Diparopsis, Syagrus, pink bollworm, and diseases If the cotton stems are left in the field after the harvest, some regrowth occurs after the first rainfall. This regrowth provides a refuge for certain pests such as Syagrus calcaratus before the new cotton plants emerge. Once the new field has abundant vegetation, pests easily migrate to it and thus inflict damage. It is therefore recommended that growers pull up the cotton plants or cut their stems after the harvest. 4. Biological control Biological control is defined as the use of living organisms or their products to combat other organisms that are considered harmful. The living organisms typically used are predators, parasites, parasitoids, and entomopathogens. A number of projects have been started in West Africa concerning the biological control of cotton pests, but they have not been continued due to practical and financial difficulties. The efforts made in this area tend to protect indigenous natural enemies by using active substances that spare them. 5. Chemical control

Despite implementation of other components of integrated control (excluding GMC), in West Africa chemical control remains the principal tool for combating cotton pests, particularly capsule caterpillars. The chemical treatment programs currently under way for cotton growing in West Africa are based on the results of large-scale experimentation, repeated over several crop years in various agro-ecological zones. The design takes into account the principal issues, namely the biological cycle of the cotton plant and the dynamics of pest populations. Two main methods of intervention have been developed on the basis of the research results:
calendar-based treatment programs,
threshold-based intervention programs. 5.1. Calendar-based treatment program The principal objective in developing a calendar-based treatment program, or predefined treatment program, was to ensure that cotton plants are protected during the entire period from the start of flowering until the majority of formed capsules have reached maturity. It took into account the very low level of expertise of growers, who did not know how to recognize the pests or manage their supplies of different products. 5.1.2. Types of calendar-based programs In West Africa, since its conception, the principle of protecting the cotton crop through a calendar-based program has involved two variants: the standard program and the windows program. o Standard program The standard program has fallen into disuse by the great majority of cotton growers. It was mostly aimed at protecting the fructiferous phase of cotton plants. The interventions began as soon as the first flowers appeared, roughly 45 to 50 days after sprouting. In general, the recommended treatment schedule was every 14 days. The number of treatments typically came to five or six for growers who adhered to the research recommendations. All the applications were done solely with a binary product (pyrethroid + organophosphorus) or occasionally a ternary product (one pyrethroid + two organophosphorus) throughout the period of protection. Unfortunately, this unvaried approach resulted in the development of resistance on the part of certain pests, particularly Helicoverpa armigera. o Windows program Development of the new calendar-based program, known as the windows program, was motivated by the appearance and then expansion of the problem of resistance to pyrethroids on the part of

-8- the Helicoverpa armigera capsule caterpillar. The principle of calendar-based interventions at 14- day intervals was maintained. Modifications were made in terms of the start-up date for treatments and the products used. The timing of the initial treatment was moved up to 30-35 days after sprouting, i.e. when the floral buds appear. The goal is to target young and fragile Helicoverpa armigera caterpillars. Based on the notion of six treatments to be carried out in order to protect a cotton field, the main innovation of this program was to create intervention “windows.” The six treatments were grouped into two or four successive interventions to form one window. Two- and three-window programs thus emerged. - Two-window program: This program is based on the principle that the first and second treatments form the first window, while the second window consists of the remaining four (third, fourth, fifth, and sixth treatments). - Three-window program: The first and second treatments form the first window; the third and fourth treatments form the second window; and the fifth and sixth treatments form the third window. It is important to note that the choice of products to be applied is made with great care. Thus: For both types of window program, the treatments of the first window are always performed with a product that does not belong to the pyrethroid family, as the objective is to reduce the duration of use of the molecules of this family, to which H. armigera has developed a resistance. A few examples include profenofos, indoxacarb, spinosad, malathion, flubendiamide- spirotetramate association, etc. During the second window (two-window program) or the last two windows (three-window program), the treatments are performed with binary products containing a pyrethroid in association with a product from a different family. In the case of the three-window program, the second window may involve the use of acaricides, followed by aphicides and/or aleurodicides during the third window. Examples of such products include:
acaricides: cypermethrine/profenofos, deltamethrine/triazophos
aphicides/aleurodicides: lambdacyhalothrine/acetamiprid, alphamethrine/imidacloprid This new strategy has been widely adopted in the subregion. It has helped stop the growing problem of caterpillar resistance to pyrethroids. In addition, it has led to greater awareness in regard to the necessity of avoiding the emergence of the same problem with other cotton crop pests. 5.2. Threshold-based program Programs of threshold-based interventions represent a very recent innovation in the subregion. Their expansion remains slow for a number of reasons related to insufficient knowledge concerning cotton pests, indisputably the determining factor in the success of this program. 5.2.1. Design This technique is based on determining infestation thresholds for the principal pests. The assortment of cotton pests in the West African subregion is indeed rich and varied, and any strategy to protect the crop must be designed with this in mind. Using an approach rooted in research results on the cotton plant and other crops coming from other regions of the world, a priority is placed on assessing the amount of damage caused by harmful insects. The results of these assessments are used to make the decision to initiate treatments and control infestations after the treatments have been performed. 5.2.2. Knowledge of insects and the damage they cause Assessing the level of infestation of insect populations requires knowledge of the various species harmful to the cotton plant and the damage they cause. To that end, samples need to be taken. 5.2.3. Sampling and decision-making The purpose of sampling is to assess populations or damage in the cotton field and then make an informed decision.

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The samples should be taken diagonally, in a homogeneous, large, and fairly representative portion of the cotton field in question. The size of the sample varies from one country to another, and the intervention threshold is related to the sample size. Readings are taken once a week, starting on the 30th day after sprouting and continuing until a majority of capsules in the cotton field have reached maturity. The basic principle is that the sampled plants must be carefully and systematically examined. In the subregion, mainly three groups of pests are taken into account in the assessments of populations and damage: carpophagous pests, phyllophagous pests, and piercing and sucking insects. While threshold- based interventions are easy with exocarpal caterpillars, the task is more complicated with endocarpal ones. The treatments are generally performed with specific products in the event that intervention thresholds are reached, or with binary products when necessary. This requires managing supplies of products of several different chemical families, a task that is not very easy for growers of the subregion. Conclusion In the case of cotton, integrated pest control in West Africa remains highly dependent on chemical controls, without which productivity cannot be assured. In the face of globalization, excessive fluctuations in world prices for cotton lint, and the subsidies granted to cotton growers in the North, the West African subregion needs to make efforts to increase field productivity in order to secure a better living for the more than 20 million persons involved in the subregion’s cotton industry. Increased productivity will require the establishment of a more favorable institutional framework, the adoption of more effective technical approaches, and better organized growers. New technologies such as the production and use of organic fertilizer with the help of activators, the protection of intervention thresholds, and genetically modified cotton may well be part of the solution.

-10- PLAN Introduction

Principaux ravageurs du cotonnier en Afrique de l’ouest

Principales maladies du cotonnier Les succès de la lutte intégrée contre les ravageurs en Afrique de l’ouest

Principales composantes de la lutte intégrée Protection semence Lutte variétale Lutte agronomique Dr Ouola TRAORE Lutte biologique Maître de Recherche, INERA/Programme Coton [email protected] Lutte chimique Conclusion 67éme réunion plénière de l’ICAC, Ouagadougou, 20 novembre 2008

INTRODUCTION Le coton est la principale culture de rente en A partir de 1990, perte d’efficacité des pyréthrinoïdes Afrique de l’Ouest avec plus de 10 millions de producteurs vis-à-vis de H. armigera en Afrique de l’ouest causant d’importantes pertes de production

En 2007, la superficie couverte par le coton était de 1,5 millions ha pour 1,2 millions tonnes de coton graine 
Malgré le Projet régional de gestion et de prévention de la résistance (PR/PRAO  PR/PICA) mis en place en 1998, Baisse des rendements: de 1000 kg/ha en 2000 à 800 kg/ pas de baisse du niveau de résistance ha en 2007. Cela s’explique par plusieurs facteurs dont les difficultés de contrôle des nuisibles 
Nécessité d’associer plusieurs méthodes de lutte (lutte intégrée) pour une meilleure protection du cotonnier Depuis 1980, utilisation de pyréthrinoïdes dans la lutte chimique

Principaux ravageurs du cotonnier en Afrique de l’ouest

1 Carpophages endocarpiques Lépidoptères phyllophages

Syllepte derogata

Cryptophlebia leucotreta Spodoptera littoralis

Anomis flava

Pectinophora gossypiella 8

Homoptères piqueurs suceurs Acariens

Les pucerons

(Aphis gossypii)
Tétranyques
: Tetranychus urticae T. neocaledonicus T. falcaratus

Les aleurodes (Bemisia tabaci)

Tarsonèmes : Polyphagotarsonemus latus

Les jassides (Jacobiella fascialis) 9

Hétéroptères

Helopelthis schoutedeni

Principales maladies du cotonnier en Afrique de l’ouest

Dysdercus völkeri

2 Maladies à la levée Bactériose Agent pathogène, une bactérie (Xanthomonas campestris)

Fontes de semis causées par :

les champignons portés par la graine (Colletotrichum, Fusarium spp..)

les champignons présents dans le sol (Rhizoctonia, Pythium, Macrophomina..)

Fusariose Virescence florale ou phyllodie

Maladie mycoplasmique transmise par une cicadelle (Orosius cellulosus)

Agent pathogène, un champignon (Fusarium oxysporium)

Pourritures des capsules

Provoquées par des champignons appartenant aux genres Xanthomonas, Colletotrichum…

Principales composantes de la Lutte Intégrée en Afrique de l’Ouest

3 La lutte intégrée?

Désinfection de la semence

ère « Système de lutte contre les organismes nuisibles en 
1 étape très importante dans la protection du cotonnier : conservation et amélioration de la levée et de utilisant un ensemble de méthodes satisfaisant les l’état sanitaire des plantules. exigences à la fois économique, écologique et toxicologique, en réservant la priorité à la mise en œuvre délibérée des 
Utilisation de l’association «
fongicides de contact et éléments naturels de limitation et en respectant les seuils insecticides (systémique ou de contact)
» contre les de tolérance ». champignons microscopiques et les ravageurs du sol (iules) et les ravageurs des jeunes plants (jassides, pucerons)


Principaux fongicides utilisés : chlorothalonil, metalaxyl, propiconazole, TMTD-Thirame, carbendazime D’où: Nécessité d’une connaissance parfaite des principaux ravageurs et maladies du cotonnier et de leurs ennemis naturels 
Principaux insecticides utilisés : benfuracarb, carbosulfan, imidaclopride, acétamipride, thiaméthoxam, chlorpyriphos éthyl, endosulfan.

Méthodes de lutte variétales Méthodes de lutte agronomiques Ensemble de pratiques culturales à même de perturber le développement d’une phase ou d’un cycle des ravageurs Il s’agit d’un ensemble de caractères induits par voie classique ou moderne pour réduire les impacts des Principales méthodes agronomiques ravageurs sur le rendement 
le labour qui met en surface de chrysalides

Quelques méthodes variétales 
le semis précoce qui permet d’éviter la période de forte pullulation de Helicoverpa armigera 
Pilosité contre les jassides 
le sarclage qui élimine les mauvaises herbes et hôtes secondaires des 
Glandes à gossypol contre les altises ravageurs, meilleure aération. 
Récoltes précoces et échelonnées qui permettent d’éviter le coton 
Cotonnier génétiquement modifié collant provoqué par les piqueurs suceurs en fin de cycle Cotonnier classique ayant reçu un gène supplémentaire issu 
la destruction des plants après récolte permet de détruire les hôtes d’un organisme différent (Bacillus thuringiensis, cas du intermédiaires de Diparopsis, Syagrus, ver rose et certaines maladies Bollgard II) . Les toxines produites sont dirigées contre les larves de lépidoptères phyllophages et carpophages. 
la rotation des cultures permet d’éviter certaines maladies présentes dans le sol. (Phase de production de semences au Burkina Faso pour la mise en culture commerciale).

Méthodes de lutte agronomiques Méthodes de lutte biologiques IMPORTANCE DE LA DATE DE SEMIS DANS LA PROTECTION DU COTONNIER Utilisation d’organismes vivants ou de leurs produits contre des organismes jugés nuisibles. MAI JUIN JUILLET AOUT SEPTEMBRE OCTOBORE NOVEMBRE Les efforts consentis ont visé la préservation des ennemis naturels indigènes par l’utilisation de substances actives peu 1er pic de 2è pic de Helicoverpa Helicoverpa nocives comme l’indoxacarb, la spinosad, … armigera armigera

Semis Méthodes de lutte chimiques Période sensible du cycle du cotonnier Précoces Malgré l’utilisation des autres composantes de la lutte intégrée, la lutte chimique reste le principal moyen de protection du cotonnier contre les principaux ravageurs Semis Période sensible du cycle du cotonnier normaux Principales familles chimiques utilisées en Afrique de l’ouest sur cotonnier : Semis Période sensible du cycle du cotonnier tardifs 
pyréthrinoïdes, 
organophosphorés, 
carbamates, 
néonicotinoïdes.

4 Les programmes de traitements - Le programme fenêtres


PROGRAMMES CALENDAIRES 
Programme à 2 fenêtres

Deux types se sont succédés
: 
Programme à 3 fenêtres

- Le programme standard ou classique Le programme fenêtre se caractérise par: Se caractérise par
: - Le démarrage précoce des traitements (30è jas)

–
Le début des traitements: premières fleurs, - Cadence des traitements: 14 jours d’intervalle

–
Intervalles de traitements : tous les 14 jours, - Nombre de traitements: 6

–
Nombres de traitements : 4 à 5 - Regroupement des traitements par 2 (3 fenêtres) –
Produit(s) utilisés
: des binaires (toute la campagne) - Le choix du produit est lié à la fenêtre

Problème
: résistance aux produits !

Choix des Produits PROGRAMMES D’INTERVENTION SUR SEUILS


Programme 3 fenêtres
: Lutte Etagée Ciblée (LEC) Le principe est basé sur une utilisation calendaire et à doses

Première fenêtre
: produit simple, réduites des insecticides et un ciblage avec des doses complémentaire lorsque les seuils sont atteints pour un ou

Seconde fenêtre
: binaire acaricide, plusieurs ravageurs.

Troisième fenêtre
: binaire aphicide,

Stratégie réalisée au Bénin et au Mali

permet de générer des économies dans les doses utilisées. 
Programme 2 fenêtres :

Seconde fenêtre
: 4 traitements avec binaire(s) Retard au déclenchement du programme de traitements foliaires

Approche
mieux adaptée aux zones à chenilles endocarpiques

Permet de générer des économies dans le nombre de traitements.

Stratégie de protection partielle sur seuil en cours en Côte d’Ivoire.

Lutte sur seuil sensu stricto CONCLUSION

La lutte intégrée en Afrique de l’ouest contre les ravageurs

Permet de générer des économies dans le nombre de du cotonnier est fortement tributaire de la lutte chimique ; traitements

Approche mieux adaptée aux zones à chenilles Face à la mondialisation (cours mondial trop fluctuant, exocarpiques subventions aux cotonculteurs du ) des efforts sont

Stratégie de protection en cours au Burkina Faso consentis en vue d’accroître la productivité des filières cotonnières de la sous région :

L’accroissement de la productivité passe la mise en œuvre d’itinéraires techniques performants, d’un cadre institutionnel favorable et une meilleure organisation OP;

La production et l’utilisation d’une fumure organique de bonne qualité et en quantité suffisante, la protection sur seuils, le coton génétiquement modifié sont autant de pistes envisageables selon le contexte de chaque pays.

5 Travail du sol pour semis précoce

Compostage de tiges de coton Champ de coton Bt

6