-1- Positive Developments in Integrated Pest Control for Cotton in

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 agroecological 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 blackishbrown 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
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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 (secondgeneration 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
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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
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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
Benfuracarb
Carbosulfan
Imidacloprid
Thiamethoxam
Chlorpyriphos ethyl
Carbendazime
Chlorothalonil
Metalaxyl
Propiconazole
TMTD - Thirame
Minimum dose
(g/kg seed)
Insecticides
1
1.25
2.5
0.15
0.5
Fungicides
0.7
1
0.35
0.15
0.75
Maximum dose
(g/kg seed)
4
2.5
3.5
1
4
4
1.6
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,
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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 midJuly 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
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the Helicoverpa armigera capsule caterpillar. The principle of calendar-based interventions at 14day 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, flubendiamidespirotetramate 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 thresholdbased 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
Les succès de la lutte intégrée contre les
ravageurs en Afrique de l’ouest
Dr Ouola TRAORE
Maître de Recherche, INERA/Programme Coton
[email protected]
67éme réunion plénière de l’ICAC, Ouagadougou, 20 novembre 2008
Principales
maladies du cotonnier
Principales
composantes de la lutte intégrée
Protection semence
Lutte variétale
Lutte agronomique
Lutte biologique
Lutte chimique
Conclusion
INTRODUCTION
Le coton est la principale culture de rente en
Afrique de l’Ouest avec plus de 10 millions de producteurs
A partir de 1990, perte d’efficacité des pyréthrinoïdes
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/
ha en 2007. Cela s’explique par plusieurs facteurs dont les
difficultés de contrôle des nuisibles
Depuis 1980, utilisation de pyréthrinoïdes dans la lutte
chimique
pas de baisse du niveau de résistance
Nécessité
d’associer plusieurs méthodes de lutte (lutte
intégrée) pour une meilleure protection du cotonnier
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
« Système de lutte contre les organismes nuisibles en
utilisant un ensemble de méthodes satisfaisant les
exigences à la fois économique, écologique et toxicologique,
en réservant la priorité à la mise en œuvre délibérée des
éléments naturels de limitation et en respectant les seuils
de tolérance ».
1ère étape très importante dans la protection du
cotonnier : conservation et amélioration de la levée et de
l’état sanitaire des plantules.
Utilisation de l’association « fongicides de contact et
insecticides (systémique ou de contact) » contre les
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
Principaux insecticides utilisés : benfuracarb,
carbosulfan, imidaclopride, acétamipride, thiaméthoxam,
chlorpyriphos éthyl, endosulfan.
D’où: Nécessité d’une connaissance parfaite des principaux
ravageurs et maladies du cotonnier et de leurs ennemis
naturels
Méthodes de lutte variétales
Il s’agit d’un ensemble de caractères induits par voie
classique ou moderne pour réduire les impacts des
ravageurs sur le rendement
Méthodes de lutte agronomiques
Ensemble de pratiques culturales à même de perturber le
développement d’une phase ou d’un cycle des ravageurs
Principales méthodes agronomiques
le labour qui met en surface de chrysalides
le semis précoce qui permet d’éviter la période de forte pullulation de
Quelques méthodes variétales
Pilosité contre les jassides
Helicoverpa armigera
le sarclage qui élimine les mauvaises herbes et hôtes secondaires des
ravageurs, meilleure aération.
Glandes à gossypol contre les altises
Récoltes précoces et échelonnées qui permettent d’éviter le coton
Cotonnier génétiquement modifié
Cotonnier classique ayant reçu un gène supplémentaire issu
d’un organisme différent (Bacillus thuringiensis, cas du
Bollgard II) . Les toxines produites sont dirigées contre les
larves de lépidoptères phyllophages et carpophages.
(Phase de production de semences au Burkina Faso pour la mise en
collant provoqué par les piqueurs suceurs en fin de cycle
la destruction des plants après récolte permet de détruire les hôtes
intermédiaires de Diparopsis, Syagrus, ver rose et certaines maladies
la rotation des cultures permet d’éviter certaines maladies présentes
dans le sol.
culture commerciale).
Méthodes de lutte biologiques
Méthodes de lutte agronomiques
IMPORTANCE
DANS
LA
MAI
JUIN
DE
LA
DATE
DE
SEMIS
PROTECTION
DU
COTONNIER
JUILLET
AOUT
SEPTEMBRE
1er pic de
Helicoverpa
armigera
Semis
Précoces
Semis
normaux
Semis
tardifs
OCTOBORE
NOVEMBRE
2è pic de
Helicoverpa
armigera
Période sensible du cycle du cotonnier
Période sensible du cycle du cotonnier
Période sensible du cycle du cotonnier
Utilisation d’organismes vivants ou de leurs produits contre
des organismes jugés nuisibles.
Les efforts consentis ont visé la préservation des ennemis
naturels indigènes par l’utilisation de substances actives peu
nocives comme l’indoxacarb, la spinosad, …
Méthodes de lutte chimiques
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
Principales familles chimiques utilisées en Afrique de
l’ouest sur cotonnier :
pyréthrinoïdes,
organophosphorés,
carbamates,
néonicotinoïdes.
4
Les programmes de traitements
PROGRAMMES CALENDAIRES
Deux types se sont succédés:
- Le programme standard ou classique
Se caractérise par:
- Le programme fenêtres
Programme à 2 fenêtres
Programme à 3 fenêtres
Le programme fenêtre 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
Programme 3 fenêtres:
Première fenêtre: produit simple,
Seconde fenêtre: binaire acaricide,
Troisième fenêtre: binaire aphicide,
Programme 2 fenêtres :
Seconde fenêtre: 4 traitements avec binaire(s)
PROGRAMMES D’INTERVENTION SUR SEUILS
Lutte Etagée Ciblée (LEC)
Le principe est basé sur une utilisation calendaire et à doses
réduites des insecticides et un ciblage avec des doses
complémentaire lorsque les seuils sont atteints pour un ou
plusieurs ravageurs.
Stratégie réalisée au Bénin et au Mali
permet de générer des économies dans les doses utilisées.
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
Permet de générer des économies dans le nombre de
traitements
Approche mieux adaptée aux zones à chenilles
exocarpiques
Stratégie de protection en cours au Burkina Faso
CONCLUSION
La lutte intégrée en Afrique de l’ouest contre les ravageurs
du cotonnier est fortement tributaire de la lutte chimique ;
Face à la mondialisation (cours mondial trop fluctuant,
subventions aux cotonculteurs du ) des efforts sont
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