**1. Introduction**

192 Fungicides for Plant and Animal Diseases

Ueno, K. Tamura, Y. & Chibana, H. (2010). Target validation and ligand development for a

Van De Wouw, A. & Howlett, B. (2011). Fungal pathogenicity genes in the age of 'omics'.

Witke, W. (2004). The role of profilin complexes in cell motility and other cellular processes.

Xu, H., Xu, H., Lin, M., Wang, W., Li, Z., Huang, J., Chen, Y., Chen, X. (2007). Learning the

*glabrata* and structure-based ligand design. *Yeast*. 27: 369–378.

drug target-likeness of a protein. *Proteomics. 7: 4255–4263*.

*Molecular Plant Pathology.* 12: 507-514.

*Trends Cell Biology.* 14: 461–469.

pathogenic fungal profilin, using a knock-down strain of pathogenic yeast *Candida* 

This chapter aims at describing an integrated approach to control the development of Black Leaf Streak Disease(BLSD) of bananas and plantains plants with a minimum of fungicide applications resulting in lower cost of control, lower risk of fungicide resistance and lower environmental negative impact.

Bananas are one of the main agricultural productions in the world, and the main fruit crop, with an annual production of about 117 Mt (Lescot, 2011). International trade of bananas represents 14Mtyear–1 with a value of more than 4 billion US\$ (Loeillet, 2005). The production of bananas for this international trade is grown in a small number of tropical countries mainly located in Latin America (80%), in African and Asian countries, and in the European community (French West Indies, Canary Islands). In all these countries, this industry is economically important and a source of direct and indirect employment. But one of the main problems is that it relies on a very narrow genetic base, the Cavendish subgroup, which is exposing the industry to important pest and disease threats.

Photo credit: CARBAP (J. Ngando) Photo 1. Banana plants with necrosis of BLSD .

An Integrated Approach to Control the Black Leaf Streak

on plantains (Stover, 1983; Mobambo et al., 1996).

banana industry is regularly increasing.

(altitude zones) (Fouré & Lescot, 1988).

diseases in the world (Pennisi, 2010).

very recent arrival in Martinique (2010).

cycle that are useful for BLSD control.

gradually evolve from stage 1 to stage 6 (Fouré, 1982)

considered to be dispersed at longer distances than conidia.

susceptible to this disease.

control BLSD to a level that does not alter fruit exportation.

Disease (BLSD) of Bananas, while Reducing Fungicide Use and Environmental Impact 195

The first one is a reduction of yield due to a negative effect on the photosynthetic assimilation (up to 50 to 100%) and thus on dry matter production. Bunch weight is strongly affected (Ramsey & Daniells, 1990), and significant yield losses (20% to 50%) were observed

A second one is a reduction of the conservation potential of the fruit, expressed by its "greenlife", which is the time between harvest and ripening, arguing for a direct effect of these foliar diseases on fruit physiology by mechanisms that remain to be discovered (Abadie et al., 2008; Chillet et al., 2009). The impact on export quality is thus very critical as there are high risks of advanced maturation (Stover, 1972). Therefore banana growers must

The economic incidence of BLSD is important since the cost of control can reach more than 25% of the production cost (Stover & Simmonds, 1987) and the BLSD incidence in the

Two species are responsible for the current epidemics, *Mycosphaerella musicola* Leach, causal agent of the Sigatoka Leaf Spot Disease (SLSD) and *Mycosphaerella fijiensis*, causal agent of the Black Leaf Streak Disease (BLSD). The latter is much more virulent than the former resulting in more intense damage and more difficult control. In addition the spectrum of susceptible varieties is much wider. The group of plantains is particularly susceptible to BLSD when it is considered resistant to SLSD, except in special geographical conditions

BLSD is regarded as the most economically important disease (Jones, 2000) for the banana industry and it is a major constraint for small farmers growing banana and plantains for domestic markets (Marin et al., 2003). It is considered as one of the most important crop

Such a situation is mainly related to the fact that the banana trade relies on a unique group of banana cultivars (*Musa acuminata*, AAA, Cavendish subgroup) which are highly

BLSD is present in Latin America since 1972, in Cameroon since 1980 and has appeared in Ivory Coast in 1985. Its expansion in the Caribbean is more recent having started from two independent introductions in the north (Cuba in 1990, and then Jamaica, the Dominican Republic, Haiti and Puerto Rico) and in the Lesser Antilles (through Trinidad in 2003) with a

The life cycle of BLSD has been widely described and starts with leaf infection by either ascospores or conidia (Fig. 1) It is important to highlight the main characteristics of this life

After a period of epiphyllic growth of generally 2-3 days, germ tubes penetrate stomata. In good conditions, the first symptoms appear generally 10-14 days after. The symptoms then

Conidia are produced on young stages of the disease (stage2-4) and have been considered as water dispersed at short distances, even if they are also present in the "airspora". Ascospores are produced at later stage and wind-dispersed after perithecia burst. They are

The Banana leaf spot diseases are a major constraint in most large production areas, resulting in very significant losses in the absence of suitable control system (Stover, 1986; Stover & Simmonds, 1987). There are two major impacts of the disease on the production.

Photos credit: CARBAP (J. Ngando)

Photo 2. Very severe attack of BLSD on a banana plant with a bunch

Photos credit: CARBAP (J. Ngando) Photo 3. Early ripening of the fruits due to severe attack of BLSD

The Banana leaf spot diseases are a major constraint in most large production areas, resulting in very significant losses in the absence of suitable control system (Stover, 1986; Stover & Simmonds, 1987). There are two major impacts of the disease on the production.

Photos credit: CARBAP (J. Ngando)

Photos credit: CARBAP (J. Ngando)

Photo 2. Very severe attack of BLSD on a banana plant with a bunch

Photo 3. Early ripening of the fruits due to severe attack of BLSD

The first one is a reduction of yield due to a negative effect on the photosynthetic assimilation (up to 50 to 100%) and thus on dry matter production. Bunch weight is strongly affected (Ramsey & Daniells, 1990), and significant yield losses (20% to 50%) were observed on plantains (Stover, 1983; Mobambo et al., 1996).

A second one is a reduction of the conservation potential of the fruit, expressed by its "greenlife", which is the time between harvest and ripening, arguing for a direct effect of these foliar diseases on fruit physiology by mechanisms that remain to be discovered (Abadie et al., 2008; Chillet et al., 2009). The impact on export quality is thus very critical as there are high risks of advanced maturation (Stover, 1972). Therefore banana growers must control BLSD to a level that does not alter fruit exportation.

The economic incidence of BLSD is important since the cost of control can reach more than 25% of the production cost (Stover & Simmonds, 1987) and the BLSD incidence in the banana industry is regularly increasing.

Two species are responsible for the current epidemics, *Mycosphaerella musicola* Leach, causal agent of the Sigatoka Leaf Spot Disease (SLSD) and *Mycosphaerella fijiensis*, causal agent of the Black Leaf Streak Disease (BLSD). The latter is much more virulent than the former resulting in more intense damage and more difficult control. In addition the spectrum of susceptible varieties is much wider. The group of plantains is particularly susceptible to BLSD when it is considered resistant to SLSD, except in special geographical conditions (altitude zones) (Fouré & Lescot, 1988).

BLSD is regarded as the most economically important disease (Jones, 2000) for the banana industry and it is a major constraint for small farmers growing banana and plantains for domestic markets (Marin et al., 2003). It is considered as one of the most important crop diseases in the world (Pennisi, 2010).

Such a situation is mainly related to the fact that the banana trade relies on a unique group of banana cultivars (*Musa acuminata*, AAA, Cavendish subgroup) which are highly susceptible to this disease.

BLSD is present in Latin America since 1972, in Cameroon since 1980 and has appeared in Ivory Coast in 1985. Its expansion in the Caribbean is more recent having started from two independent introductions in the north (Cuba in 1990, and then Jamaica, the Dominican Republic, Haiti and Puerto Rico) and in the Lesser Antilles (through Trinidad in 2003) with a very recent arrival in Martinique (2010).

The life cycle of BLSD has been widely described and starts with leaf infection by either ascospores or conidia (Fig. 1) It is important to highlight the main characteristics of this life cycle that are useful for BLSD control.

After a period of epiphyllic growth of generally 2-3 days, germ tubes penetrate stomata. In good conditions, the first symptoms appear generally 10-14 days after. The symptoms then gradually evolve from stage 1 to stage 6 (Fouré, 1982)

Conidia are produced on young stages of the disease (stage2-4) and have been considered as water dispersed at short distances, even if they are also present in the "airspora". Ascospores are produced at later stage and wind-dispersed after perithecia burst. They are considered to be dispersed at longer distances than conidia.

An Integrated Approach to Control the Black Leaf Streak

Disease (BLSD) of Bananas, while Reducing Fungicide Use and Environmental Impact 197

 Photo 4. Stages 1 and 2 of the disease Photo 5. Stages 2 and 3 of the disease

 Photo 6. Stages 4 (adaxial surface) Photo 7. Stages 5 of the disease

Photo 8. Stage 6 of the disease with Photo 9. The density of infection is perithecia (abaxial surface). often very important resulting in necrotic patches by coalescence.

Plate 1. **Illustration of BLSD symptoms** (Photo credit: Cirad /E.Fouré & L. de Lapeyre de

Bellaire)

(adaxial surface) (adaxial surface)

(abaxial surface)

*( in yellow: data for the Sigatoka Disease and in black, data for the BLSD)* 

Fig. 1. The biological cycle of the banana leaf spot diseases

#### **2. Principle and various components of an integrated approach to control BLSD of bananas**

The principle and various components of this integrated approach are presented. They are based on a holistic approach including technical aspects and logistical, economic and political aspects as well.

#### **2.1 Historical features**

It is useful to look at some historical features to better understand the genesis of this integrated control of BLSD.

An effective chemical control of SLSD, based on the use of mineral oils, was developed by a French team of IFAC in Guadeloupe in the fifties (Guyot &Cuillé, 1954; Guyot &Cuillé, 1955).

The work done at that time quickly showed that the foliar emission rate of the banana plant would impose a very large number of sprays to ensure that each new leaf is protected in time. This should lead to a minimum of forty sprays per year with an additional processing constraint to apply about 2000 liters of aqueous formulation per hectare, which was quite intolerable.

(adaxial surface) (adaxial surface)

*( in yellow: data for the Sigatoka Disease and in black, data for the BLSD)*  Fig. 1. The biological cycle of the banana leaf spot diseases

**BLSD of bananas** 

political aspects as well.

**2.1 Historical features** 

intolerable.

integrated control of BLSD.

**2. Principle and various components of an integrated approach to control** 

The principle and various components of this integrated approach are presented. They are based on a holistic approach including technical aspects and logistical, economic and

It is useful to look at some historical features to better understand the genesis of this

An effective chemical control of SLSD, based on the use of mineral oils, was developed by a French team of IFAC in Guadeloupe in the fifties (Guyot &Cuillé, 1954; Guyot &Cuillé, 1955). The work done at that time quickly showed that the foliar emission rate of the banana plant would impose a very large number of sprays to ensure that each new leaf is protected in time. This should lead to a minimum of forty sprays per year with an additional processing constraint to apply about 2000 liters of aqueous formulation per hectare, which was quite

Photo 4. Stages 1 and 2 of the disease Photo 5. Stages 2 and 3 of the disease

Photo 6. Stages 4 (adaxial surface) Photo 7. Stages 5 of the disease

(abaxial surface)

Photo 8. Stage 6 of the disease with Photo 9. The density of infection is perithecia (abaxial surface). often very important resulting in

necrotic patches by coalescence.

Plate 1. **Illustration of BLSD symptoms** (Photo credit: Cirad /E.Fouré & L. de Lapeyre de Bellaire)

An Integrated Approach to Control the Black Leaf Streak

crop practices)

(from de Lapeyre et al., 2009)

emulsions or water.

fungicides with mineral oil (oil compatible formulations)


Disease (BLSD) of Bananas, while Reducing Fungicide Use and Environmental Impact 199




Fig. 2. Fungicide use for SLSD control in commercial banana farms of Guadeloupe (1969-2006).

This warning strategy developed by IRFA was very different from the systematic strategy used by U.S. companies using contact fungicides in water or systemic fungicides in oil

The research therefore looked for reducing these constraints i) by studying more closely the biology of the pathogen to intervene only when necessary ii) limiting the volume of mixture applied per hectare and the number of fungicide applications, iii ) focusing on the choice of more effective and persistent fungicides.

The first goal resulted in the development of disease observation and warning methods, with the early work conducted by Cuillé & Guyot in 1954.

To reach the second goal, the work achieved made it possible to replace the copper formulations applied through ground sprays at a rate of 2000 liters per hectare by a low volume of mixtures, initially applied with ground sprayers and later by plane or helicopter, to go down to 15 liters per hectare. This development was made possible by the discovery of the qualities of mineral oils which have proven to be excellent vehicles for fungicides, either alone or mixed with water. These mineral oils (i) showed a fungistatic activity on the pathogen, (ii) ensured a good repartition of droplets at leaf surface and a good penetration of fungicides in the leaf tissues, (iii)avoided the rainfall leaching occurring after treatment.

As a matter of fact, before 1972, aerial and ground sprays were currently done only with oil. With the appearance of systemic fungicides in the 1970', new formulations were introduced coupling the fungistatic action of the oil with the strong curative action of currently marketed systemic fungicides (Ganry & Laville, 1983). Fungicides used belong to different chemical families with different mode of actions such as benzimidazoles, triazoles, morpholins and more recently strobilurins (see Box 4), which have been used practically in this chronological order, taking into account the emergence of resistance of the fungus to benzimidazoles and triazoles..

Very soon appeared the need to abandon a strategy of systematic control and move towards less fungicide applications in order to (i) reduce production costs, (ii) reduce environmental impact and (iii) limit the occurrence of fungicide resistant strains. With such an objective of better management of the control strategy, CIRAD (formerly IRFA) has, since the seventies, focused its work on the development of a warning method in order to apply fungicides only when necessary.

The warning system used is based both on climatic data (Box 1) and on field observations of symptoms evolution in early stages (Box 2).

In Guadeloupe and Martinique, since the 70's, the information has been processed on an aggregate basis for each island and managed by a specialized team attached to the banana growers associations. Aerial sprays are made on a similar base and are generalized for the whole of each island.

As a result of the use of such a disease management strategy the control of the SLSD has been very satisfactory in the French Antilles since the seventies (Fig. 1), with a number of applications ranging from five to eight per year, while applications carried out systematically in similar situations would have required at least 10 to 15 treatments per year (Ganry, 2001).

This success story relies on some basic requirements:


The research therefore looked for reducing these constraints i) by studying more closely the biology of the pathogen to intervene only when necessary ii) limiting the volume of mixture applied per hectare and the number of fungicide applications, iii ) focusing on the choice of

The first goal resulted in the development of disease observation and warning methods,

To reach the second goal, the work achieved made it possible to replace the copper formulations applied through ground sprays at a rate of 2000 liters per hectare by a low volume of mixtures, initially applied with ground sprayers and later by plane or helicopter, to go down to 15 liters per hectare. This development was made possible by the discovery of the qualities of mineral oils which have proven to be excellent vehicles for fungicides, either alone or mixed with water. These mineral oils (i) showed a fungistatic activity on the pathogen, (ii) ensured a good repartition of droplets at leaf surface and a good penetration of fungicides in the leaf tissues, (iii)avoided the rainfall leaching occurring after treatment. As a matter of fact, before 1972, aerial and ground sprays were currently done only with oil. With the appearance of systemic fungicides in the 1970', new formulations were introduced coupling the fungistatic action of the oil with the strong curative action of currently marketed systemic fungicides (Ganry & Laville, 1983). Fungicides used belong to different chemical families with different mode of actions such as benzimidazoles, triazoles, morpholins and more recently strobilurins (see Box 4), which have been used practically in this chronological order, taking into account the emergence of resistance of the fungus to

Very soon appeared the need to abandon a strategy of systematic control and move towards less fungicide applications in order to (i) reduce production costs, (ii) reduce environmental impact and (iii) limit the occurrence of fungicide resistant strains. With such an objective of better management of the control strategy, CIRAD (formerly IRFA) has, since the seventies, focused its work on the development of a warning method in order to apply fungicides only

The warning system used is based both on climatic data (Box 1) and on field observations of

In Guadeloupe and Martinique, since the 70's, the information has been processed on an aggregate basis for each island and managed by a specialized team attached to the banana growers associations. Aerial sprays are made on a similar base and are generalized for the

As a result of the use of such a disease management strategy the control of the SLSD has been very satisfactory in the French Antilles since the seventies (Fig. 1), with a number of applications ranging from five to eight per year, while applications carried out systematically in similar situations would have required at least 10 to 15 treatments per year (Ganry, 2001).


more effective and persistent fungicides.

benzimidazoles and triazoles..

symptoms evolution in early stages (Box 2).

This success story relies on some basic requirements:

the completion of the spray.

when necessary.

whole of each island.

with the early work conducted by Cuillé & Guyot in 1954.

Fig. 2. Fungicide use for SLSD control in commercial banana farms of Guadeloupe (1969-2006). (from de Lapeyre et al., 2009)

This warning strategy developed by IRFA was very different from the systematic strategy used by U.S. companies using contact fungicides in water or systemic fungicides in oil emulsions or water.

An Integrated Approach to Control the Black Leaf Streak

crop density, water management.

curative, fungicides are used (Table 1.).

10 to 15 sprays a year (depending on

curative (systemic) fungicide

location and inoculums)

Oil used with a rate of 12-15 liters/ha with

a vicious circle.

selection pressure.

Disease (BLSD) of Bananas, while Reducing Fungicide Use and Environmental Impact 201

eliminate new sources of inoculum. Other crop practices must be introduced to synergize with fungicide sprays and leaf removal dealing with crop management: plant nutrition,

Depending on the type of fungicide used and on the selection pressure1, there is always a risk of emergence of fungicide resistance in pathogen populations. It is one of the major reasons of the decrease of the chemical control efficiency which is often the starting point of

Therefore it is highly important to monitor the pathogen sensitivity to the fungicides used. This monitoring must be considered as a key decision tool for the choice of appropriate fungicides (when it is possible) and their sequence in alternation, in order to minimize the

Such an approach was adopted for BLSD when it appeared in Gabon on plantains (see §2.2. BLSD control in Gabon in small scale plantain production for domestic markets) and in Cameroon (see §2.2. BLSD control in Cameroon in the banana industry for export), Ivory Coast and Ecuador on banana and plantain. Thanks to a strong experience on SLSD control and to the implementation of such disease management strategies, BLSD in these countries

In comparison, in some Latin American countries, the number of annual sprays can reach 30 to 60 (more than one per week) due to systematic fungicide applications and to the emergence of resistant strains to curative (systemic) fungicides that were used too frequently (Carlier et al., 2000; Romero & Sutton, 1997). As a consequence more contact, non

Water or oil-water emulsions (2 – 8 liters of

oil + 10-20 liters of water) with

3. Contact and curative fungicide 30 to 60 systematic sprays depending on

1. Contact fungicide 2. Curative fungicide

locations

Table 1. Compared characteristics of the IRFA and american methods for BLSD control

The timing of decisions is based on a standardized set of criteria, taking into account the development of the fungus and the growth of the plant, both climate-driven. The first level

2 Cameroon: from 10 to 15 treatments / year have succeeded in the disease control for more than 10 years. However, the emergence of strains resistant to systemic fungicides, due to some failures in the



**2.2.1 Component 1: Timing of decisions through a biological forecasting** 

1 Related to the duration of the pathogen exposure to the fungicide

implementation, is currently preventing the use of this disease management.

management strategy was experimented in this country in the late 80's.

has been properly controlled with an average of 10 to 15 treatments per year2.

IRFA method american method

The characteristics of these two control methods are summarized in the table 1.

#### **2.2 The basic principle of an integrated approach to control the banana BLSD**

Inherited from this strong experience with the control of the SLSD, the integrated approach to control BLSD is based on the rational use of curative (systemic) fungicides applied in oil mixtures.

The sequence of fungicide sprays is driven by a forecasting system supported by biological indicators (Fouré & Ganry, 2008; Ganry et al., 2008). Since *M. fijiensis* is more aggressive than *M. musicola*, the system works efficiently for this pathogen when the disease pressure is not too high. It is the reason why it must be supplemented by sanitation practices consisting in necrotic and pre-necrotic leaf removal in order to

The characteristics of these two control methods are summarized in the table 1.

**2.2 The basic principle of an integrated approach to control the banana BLSD** 

mixtures.

Inherited from this strong experience with the control of the SLSD, the integrated approach to control BLSD is based on the rational use of curative (systemic) fungicides applied in oil

The sequence of fungicide sprays is driven by a forecasting system supported by biological indicators (Fouré & Ganry, 2008; Ganry et al., 2008). Since *M. fijiensis* is more aggressive than *M. musicola*, the system works efficiently for this pathogen when the disease pressure is not too high. It is the reason why it must be supplemented by sanitation practices consisting in necrotic and pre-necrotic leaf removal in order to eliminate new sources of inoculum. Other crop practices must be introduced to synergize with fungicide sprays and leaf removal dealing with crop management: plant nutrition, crop density, water management.

Depending on the type of fungicide used and on the selection pressure1, there is always a risk of emergence of fungicide resistance in pathogen populations. It is one of the major reasons of the decrease of the chemical control efficiency which is often the starting point of a vicious circle.

Therefore it is highly important to monitor the pathogen sensitivity to the fungicides used. This monitoring must be considered as a key decision tool for the choice of appropriate fungicides (when it is possible) and their sequence in alternation, in order to minimize the selection pressure.

Such an approach was adopted for BLSD when it appeared in Gabon on plantains (see §2.2. BLSD control in Gabon in small scale plantain production for domestic markets) and in Cameroon (see §2.2. BLSD control in Cameroon in the banana industry for export), Ivory Coast and Ecuador on banana and plantain. Thanks to a strong experience on SLSD control and to the implementation of such disease management strategies, BLSD in these countries has been properly controlled with an average of 10 to 15 treatments per year2.

In comparison, in some Latin American countries, the number of annual sprays can reach 30 to 60 (more than one per week) due to systematic fungicide applications and to the emergence of resistant strains to curative (systemic) fungicides that were used too frequently (Carlier et al., 2000; Romero & Sutton, 1997). As a consequence more contact, non curative, fungicides are used (Table 1.).


Table 1. Compared characteristics of the IRFA and american methods for BLSD control

### **2.2.1 Component 1: Timing of decisions through a biological forecasting**

The timing of decisions is based on a standardized set of criteria, taking into account the development of the fungus and the growth of the plant, both climate-driven. The first level

<sup>1</sup> Related to the duration of the pathogen exposure to the fungicide

<sup>2</sup> Cameroon: from 10 to 15 treatments / year have succeeded in the disease control for more than 10 years. However, the emergence of strains resistant to systemic fungicides, due to some failures in the implementation, is currently preventing the use of this disease management.

<sup>-</sup> Ivory Coast: control is achieved with 12-14 treatments / year in most production areas.

<sup>-</sup> Ecuador: from 10 to 12 treatments / year succeeded in disease control when this disease management strategy was experimented in this country in the late 80's.

An Integrated Approach to Control the Black Leaf Streak

efficiency of the chemical strategy at the harvest stage.

Disease (BLSD) of Bananas, while Reducing Fungicide Use and Environmental Impact 203


of elaboration of reliable tools for strategic decisions is to implement a continuous monitoring of disease evolution in the field. It is also informative to fit these weekly data with weekly rainfall, in order to get a better appreciation of epidemiological conditions **(**de Lapeyre de Bellaire et al., 2010a).


SEDb represents the speed of evolution of the disease, which reflects the climatic conditions and the intensity of the infection (Ganry & Meyer, 1972b). The early detection of new attacks on the youngest leaves will allow blocking their evolution towards necroses thanks to the application of a curative fungicide. In order to maintain the field inoculum as low as possible, it is then essential to stop the disease evolution before necrotic formation because sexual sporulation starts in necrotic stages of the disease.

A larger set of disease parameters should also be used and evaluated continuously every week on the same banana plot used for the assessment of SEDb in order to provide complementary information:


of elaboration of reliable tools for strategic decisions is to implement a continuous monitoring of disease evolution in the field. It is also informative to fit these weekly data with weekly rainfall, in order to get a better appreciation of epidemiological conditions **(**de


SEDb represents the speed of evolution of the disease, which reflects the climatic conditions and the intensity of the infection (Ganry & Meyer, 1972b). The early detection of new attacks on the youngest leaves will allow blocking their evolution towards necroses thanks to the application of a curative fungicide. In order to maintain the field inoculum as low as possible, it is then essential to stop the disease evolution before necrotic formation because

A larger set of disease parameters should also be used and evaluated continuously every week on the same banana plot used for the assessment of SEDb in order to provide



Lapeyre de Bellaire et al., 2010a).

leaves (Fig. 3).

complementary information:

the older leaves.

sexual sporulation starts in necrotic stages of the disease.

to slow down the necrotic formation (Fig. 4).


An Integrated Approach to Control the Black Leaf Streak

Disease (BLSD) of Bananas, while Reducing Fungicide Use and Environmental Impact 205

Fig. 4. Illustration of interpretation of the Youngest Leaf Spotted (YLS) from its weekly evolution in banana plantations**.** *Arrows indicate the date at which the whole 10 banana plants where changed At that date, the variation should not be considered as the value of YLS is artificially different. YLS is scored according to Stover's method* (from de Lapeyre de Bellaire et al., 2010a)

The timing of the fungicide applications is driven by SEDb and the analysis of other

The time between decision and execution of one application should not exceed 2 days. Sprays are carried out by airplane, helicopter, or by backpack sprayer on small surfaces. However, care must be taken with the climatic conditions of aerial spraying: only a small window, early in the morning and late in the afternoon, is suitable; otherwise, thermal inversion and air turbulence do not allow correct spray deposition. Aerial application is not possible on rainy and windy days. Logistics available is therefore essential to optimize

**The efficiency of sprays** is dependent on the quality of the foliar application, and a good

The weather conditions the day of application are critical: temperature must be rather cool (less than 28°C) and wind as low as possible (<1.3 m.s-1) and regular. Sprayers and nozzles must be cleaned every day and calibrated frequently (calibration depends on the use of water or oil and on the rate of mixture used per ha). Significant technical improvement has

**2.2.2 Component 2: Timing and quality of the fungicide applications** 

spraying during this small window.

been achieved when aircraft are guided precisely by GPS.

coverage is essential.

parameters. It is the reason why it must be implemented by highly skilled teams.



Table 2. Example of a data sheet used for the calculation of the weekly SEDb in banana plants (FER = Foliar Emission Rate) *( from Fouré &Ganry, 2008)*

Fig. 3. Illustration of the Stage of Evolution of Disease's (SEDb) potential to forecast fungicide applications and to monitor the efficiency of the chemical control strategy in banana plantations. *All fungicide applications are indicated by an arrow above the SEDb curve (arrows with different colors correspond to different fungicides applied)* (from de Lapeyre de Bellaire et al., 2010a)

Table 2. Example of a data sheet used for the calculation of the weekly SEDb in banana

Fig. 3. Illustration of the Stage of Evolution of Disease's (SEDb) potential to forecast fungicide

plantations. *All fungicide applications are indicated by an arrow above the SEDb curve (arrows with different colors correspond to different fungicides applied)* (from de Lapeyre de Bellaire et al., 2010a)

applications and to monitor the efficiency of the chemical control strategy in banana

plants (FER = Foliar Emission Rate) *( from Fouré &Ganry, 2008)*

Fig. 4. Illustration of interpretation of the Youngest Leaf Spotted (YLS) from its weekly evolution in banana plantations**.** *Arrows indicate the date at which the whole 10 banana plants where changed At that date, the variation should not be considered as the value of YLS is artificially different. YLS is scored according to Stover's method* (from de Lapeyre de Bellaire et al., 2010a)

#### **2.2.2 Component 2: Timing and quality of the fungicide applications**

The timing of the fungicide applications is driven by SEDb and the analysis of other parameters. It is the reason why it must be implemented by highly skilled teams.

The time between decision and execution of one application should not exceed 2 days. Sprays are carried out by airplane, helicopter, or by backpack sprayer on small surfaces. However, care must be taken with the climatic conditions of aerial spraying: only a small window, early in the morning and late in the afternoon, is suitable; otherwise, thermal inversion and air turbulence do not allow correct spray deposition. Aerial application is not possible on rainy and windy days. Logistics available is therefore essential to optimize spraying during this small window.

**The efficiency of sprays** is dependent on the quality of the foliar application, and a good coverage is essential.

The weather conditions the day of application are critical: temperature must be rather cool (less than 28°C) and wind as low as possible (<1.3 m.s-1) and regular. Sprayers and nozzles must be cleaned every day and calibrated frequently (calibration depends on the use of water or oil and on the rate of mixture used per ha). Significant technical improvement has been achieved when aircraft are guided precisely by GPS.

An Integrated Approach to Control the Black Leaf Streak

preliminary field experiments.

Disease (BLSD) of Bananas, while Reducing Fungicide Use and Environmental Impact 207

The use of these fungicides in pure oil strengthens their curative effect, because mineral oils are fungistatic. Attention should be paid to the formulation of the fungicide used. Only formulations compatible with pure oil should be used. Phytotoxic effects of the oil have to be preliminarily determined. Fungicide concentration must also be determined according to

It is achieved through prophylactic leaf removal coupled with relevant crop management,

The experience of BLSD control in Gabon (see §2.2) has clearly shown that when plantain fields were isolated into a forest environment and far from infected plots, preventing them

Thus, keeping the sources of inoculum at a very low level is very important to ensure the success of the chemical control strategy. Where extensive spotting is present, new infections will develop quickly because chemical sprays do not remove the disease from spotted leaves and the only solution is to remove them mechanically from the banana tree. Therefore, such necrotic leaf removal must be a regular practice in banana growing countries where BLSD is present. It should be based on a risk management approach, taking into account that it could

Experimental leaf removal has shown that bunch weight, the main yield component, is poorly affected as long as 5 to 7 leaves remain on the plant from flowering to harvest (Ramsey et al., 1990; Daniells et al., 1994; Vargas et al., 2009). A stronger leaf removal could affect the final yield. In addition a lack of resources during this phase, due to severe spotting could compromise the yield of the next ratoon (Eckstein et al., 1995; Dens et al., 2008).

Leaf removal is particularly needed in critical areas where regular sprays are not well performed due to natural obstacles or to regulatory measures such as in buffer areas where aerial spraying is prohibited (e.g. 50 m from houses, gardens, rivers and roads in the FWI). A strong communication effort should be done towards the farm managers in order to improve the situation, because the chemical control strategy will not be successful if the leaf removal is not done properly. Such leaf removal might be mandatory on BLSD susceptible banana plants that cannot be part of the spraying agenda: in home gardens, near houses, along roads or rivers. In such situations the best solution would be to replace the susceptible bananas by resistant varieties. It requires to take into account social and political components, such as the acceptability of these varieties by the consumers in order to encourage voluntary behavior. In some cases like in Australia, more coercive measures were used with an objective of complete

In addition it is essential to destroy systematically all abandoned plantations and isolated

In areas where fungicide sprays are done, it is essential to realize necrotic leaf removal before any fungicide spray in order to lower the inoculum pressure and thus enhance the efficiency of the fungicide and to minimize the exposure of the pathogen to the fungicide

**2.2.3 Component 3: The control of the inoculum pressure in the field** 

from external contamination, the disease control was strongly facilitated.

eradication which was successfully achieved (Henderson et al., 2006).

and thus the risk of appearance of resistant strains to the fungicide.

roadside banana plants that are potential reservoir of disease inoculums.

such as plant density and water and fertilizer management.

affect the production beyond certain level.

An irregular topography of the zone or the presence of obstacles might alter the uniformity of the treatment. The banana plots must be shaped to facilitate aerial sprays, taking into account the presence of obstacles and wind drift, and the crop density should not be too high to allow good penetration of the fungicide spray. A strong synergy between the aerial spraying companies and the banana growers is also important to ensure the quality of the aerial applications.

The use of mineral oils as a carrier considerably improves the quality of coverage through aerial spraying with low volumes (12–15 Lha–1). The quality of oil is essential and must fit with the norms defined by Cuillé and Blanchet in 1958 and always used. The quality of the mix with the fungicide is important as well. Fungicides must be used at full rate in order to limit the risk of fungicide resistance.


Table 3. Characteristics of oil used for sprays in the control of SLSD (Cuillé & Blanchet, 1958)

The efficiency of treatments relies on a strong curative effect. Thus, systemic fungicides (antimitotics, sterol inhibitors of group 1 and 2, strobilurines, pyrimidins) are preferred to contact fungicides (see Box 4).


An irregular topography of the zone or the presence of obstacles might alter the uniformity of the treatment. The banana plots must be shaped to facilitate aerial sprays, taking into account the presence of obstacles and wind drift, and the crop density should not be too high to allow good penetration of the fungicide spray. A strong synergy between the aerial spraying companies and the banana growers is also important to ensure the quality of the

The use of mineral oils as a carrier considerably improves the quality of coverage through aerial spraying with low volumes (12–15 Lha–1). The quality of oil is essential and must fit with the norms defined by Cuillé and Blanchet in 1958 and always used. The quality of the mix with the fungicide is important as well. Fungicides must be used at full rate in order to

**Characteristics norms** 

Viscosity 4 à 7° Engler at 20°C Density 0.83 to 0.90 Sulfonation index 85-90% maximum

Acidity less than 0.16 Addition ingredients no sulfur compound

Table 3. Characteristics of oil used for sprays in the control of SLSD (Cuillé & Blanchet, 1958)

The efficiency of treatments relies on a strong curative effect. Thus, systemic fungicides (antimitotics, sterol inhibitors of group 1 and 2, strobilurines, pyrimidins) are preferred to

> Contact fungicides (mancozeb, chlorothalonil) have only a preventive effect and do not penetrate in the banana leaf. They are generally applied every week in systematic frameworks because all new unfurling banana leaf must be protected. They have a multi-site effect on fungal biology and strains resistant to these fungicides have never been

> Systemic fungicides penetrate in the banana leaf. The systemic properties of these fungicides are variable: some have only a translaminar transport and others can be distributed in the whole banana plant, and the biokinetics of these fungicides confer a more or less pronounced curative effect. The curative effect is more pronounced on young streaks (stages 1, 2), but lower on older lesions (stages 3, 4) and without any effect on necrotic stages (stages 5, 6), even if

> - Inhibitors of ergosterol biosynthesis (IBS) in group 1 that inhibit eburicol demethylation (DMI fungicides mostly




sporulation might be temporarily decreased. Different chemical families have been used:


Type indifferently paraffinic or naphtenic

aerial applications.

limit the risk of fungicide resistance.

contact fungicides (see Box 4).

*a. Protectants* 

reported. *b. Systemic fungicides* 

**Box 4. Various categories of fungicides used for BLSD control** 

Three groups have a strong curative effect:

Two groups have a moderate curative effect:

very high risk of resistance

moderate risk of resistance

resistance

belonging to the triazole family): high risk of resistance

The use of these fungicides in pure oil strengthens their curative effect, because mineral oils are fungistatic. Attention should be paid to the formulation of the fungicide used. Only formulations compatible with pure oil should be used. Phytotoxic effects of the oil have to be preliminarily determined. Fungicide concentration must also be determined according to preliminary field experiments.
