CHAPTER V: AFRICA

PROMISING ALTERNATIVES IN KENYA AND MOROCCO

M. Ammati* and B. Nyambo**

*Department of Plant Pathology, Institut Agronomique et Vétérinaire Hassan II, BP6202 Rabat, Morocco
** Integrated Crop Management Practitioner, P. O. Box 90, Village Market-Nairobi, Kenya

Summary. In Kenya the importation of MeBr is decreasing, as result of the use of alternatives to this soil fumigant. Also in Morocco other means to control soil pests are being used. Growers are using cultural practices, other pesticides, Negative Pressure Soil Steam Sterilization, soil solarization in combination with fumigants, and biofumigation. These alternatives also proved to be cost effective.

Key Words: Methyl Bromide, alternatives, cultural practices, sanitation, steam sterilization, soil solarization, biofumigation

I. INTRODUCTION

Kenya is one of the countries in Eastern Africa with high consumption of MeBr as a soil fumigant to control soil-borne pests (diseases, nematodes, insect pests, weeds etc.) in the production of cut flowers (carnations, roses, and aster and chrysanthemum cuttings) and strawberries (Schonfield, Wamukonya and Glendening, 1994). The use of MeBr in cut flowers and strawberries is popular with growers because of its effectiveness in controlling a wide range of soilborne pests, cost effectiveness and ease of use. However, since the introduction of the Montreal Protocol in 1992, Kenya committed herself to the principles of the Protocol to phase-out the use of MeBr by the year 2015. As a result, the annual importation of MeBr stabilized at about 330 tons per year between 1994 and 1996, with 70 % of it used for soil fumigation in cut flower production (Klijnstra, 1999). During the same period, the combined total acreage under carnations, roses and chrysanthemums, the main crops requiring the use of MeBr, increased by 26.5 % (Malins, et al, 1998). It can therefore be assumed that the total consumption for soil fumigation is declining as well. The phase-out will in no doubt affect production and export of cut flowers and strawberries. However, continued use will have negative economic impact mostly as a result of International trade restrictions. To address the issue and to avoid the consequences of non-conformity to the Montreal Protocol, Kenya farmers and research institutions have been actively developing and validating suitable alternatives to MeBr for use in Kenya production systems (Klijnstra, 1999). The cut flower and strawberry production sub sectors are highly privatized and the flow of technical information is minimal (M. Wabule and R. S. Malik, personal communication). Many of the growers, particularly the large-scale farmers, carry out on-farm validation of suitable MeBr alternatives to address farm needs, and the information so generated is not available to the public. Thus, the reduced imports of MeBr as discussed above are evidence of declining demand for the product within Kenya, although the consumption for soil fumigation does not show a proportional decline. The observed reduced demand is evidence to the fact that the large users of MeBr are gradually becoming less dependent on the chemical as they embrace new alternatives in their production systems.

In Morocco, the use of nematicides increased from 300 tons in 1986 to 2000 tons in 1993. Among these nematicides, metam sodium and MeBr are widely applied in soil fumigation of tomato grown under plastic houses. Because they are difficult to handle, the granulars are occasionally used at planting time, even in combination with resistant, or tolerant varieties to root knot nematodes. Repeated use of nematicides on tomato and other cash crops have resulted in an accelerated bio-degradation of these chemicals and their failure to control Meloidogyne spp. Subsequently the application rates became very high compared to the recommended doses. These failures to control heavy root-knot nematode infestations associated with tomato growing in sandy soils under greenhouse conditions have encouraged the use of MeBr. MeBr was introduced for the first time in Morocco in 1952 and was used only in quarantine for controlling pests associated with agricultural products. In 1987, the use of MeBr (2 % Chloropicrin) was extended to soil disinfestation. The importers are also the distributors and the only authorised institutions to apply MeBr. The consumption of MeBr in 2000 was estimated at 1295 tons. Most of this consumption is used for soil fumigation and only a small amount (about 500 kg / year) is used in quarantine. The method of application is the one commonly known as "hot gas method": MeBr is vaporised in a heat exchange device and delivered as a gas to the field to be fumigated, in a perforated polyethylene tubing pre-placed on top of the soil before spreading the plastic sheet. The application rate of MeBr varies from 70 to 90 g / m2 depending on the pests presents in soil. It is applied either locally, only on seed bed, 80 - 100 cm wide, or as an overall treatment to the whole field. The first option is the most common. This second technique uses approximately 700 Kg of MeBr per hectare compared to 300 Kg / ha as local application.

Most of the crops requiring soil fumigation are those conducted under plastic houses such as tomato, melon, watermelon, cucumber, strawberry, banana, and carnation. The period of application could be throughout the year but most of the treatments are concentrated during June-August, depending on the nature of crops conducted under plastic houses. The major soil pests controlled by MeBr are commonly root-knot nematodes for vegetable crops, ornamentals and fruit crops and occasionally Fusarium and Verticillium wilts. In Morocco, validated alternatives to MeBr in soil disinfestation were selected among others in the tomato sub-sector. Results obtained along a UNIDO (MP/126/MOR/97) demonstration project are reported. This project was implemented during the period 1998-2000. The alternatives described were tested on soils severely infested by root-knot nematodes (Meloidogyne javanica) and within an Integrated Pest Management (IPM) strategy.

II. KENYA¹

Cut flowers

Alternative chemical pesticides

About 7 % of the Kenyan Flower Council (KFC) members have replaced MeBr with dazomet and another 14 % are practising IPM (KFC personal communication).

Use of soilless culture

A few growers are converting their production systems from soil based to hydroponics (personal observations, KFC personal communication). The most common substrates used by these large growers include pumice (locally mined in the production vicinity), and coconut husks (imported as cocospeat from Asia).

One farmer who has been growing roses using pumice as a substrate over the last 10 years, has completely eliminated the use of MeBr. Replanting was done without any soil treatment and there was no outbreak of soilborne pests in the new crop.

The use of cocospeat is a new introduction in the cut flower industry in East Africa and many farmers are still at the experimental stage. According to a farmer, who has been trying it out during the last three years, the use of cocospeat is 30 % more expensive than soil based systems, (needs frequent collection of technical data to optimise the approach and uses higher amounts of fertiliser) but gives more stems / m2 which are also of better quality. The other limitation to wider use of cocospeat is local availability. The experimental material being used in the farms is imported from Asia, notably Indonesia and Sri-Lanka.

Use of natural pesticides

Mexican marigold, Tagetes sp., has also been tried by some farmers for the control of root-knot nematodes (Patel, 1999; Klijnstra, 1999) in cut flower production. According to Patel (1999), the use of Tagetes extract gave effective control of root knot nematodes in commercial roses. Similarly, using Tagetes as a fallow crop prior to planting roses delayed the onset of pest infection on mature roses while incorporating chopped material of the weed in the soil prior to planting improved the health of the plants and reduced attacks by root knot nematodes. The farmer found out that the best results were obtained when the chopped material of the plant were incorporated into the soil in combination with the application of an appropriate pesticide.

Compost

A farmer has tried a combination of metam sodium and mushroom compost for two years and coconut compost (locally bought from the Coast) for about 4 years in the production of calla lilies. Coconut compost is a by-product of coconut processing, mostly the sawdust, which is left to undergo natural decomposing.

Currently, the farmer uses the coconut compost as manure and in this allowed him to reduce the consumption of synthetic fertilisers by 30 to 40 % and also reduced soilborne pathogens. The farmer finds the coconut compost much cheaper than mushroom compost. The coconut compost has good water holding capacity and therefore can also be used in hydroponics. Metam sodium is used for soil fumigation once a year in the production of bulbs to minimise the outbreak of soilborne pathogens, particularly before planting a new crop.

Strawberries

The majority of small-scale farmers use cultural methods to control the major soilborne pest problems (Mungai, 1995).

Use of clean planting materials

This is has been accepted by growers and is widely practised even by medium and large growers.

Mulching

Farmers are advised to use black polyethylene mulch as this gives effective weed control. The black polyethylene also helps to conserve soil moisture, keeps the soil warm and the fruits clean.

Sanitation

This involves the removal and burning of crop residues after every two months of continuous production.

Crop rotation

A two to three year's rotation is advised. Farmers should start with clean planting materials.

Roguing

Uproot and destroy all plants affected by viral diseases. However, the recommended cultural practices have not offered solutions to all soilborne and viral pathogens that constrain economic production of strawberries. Medium and large growers (> one acre under production) have been experimenting with other pest control methods that will ultimately be able to replace MeBr in the production of strawberries.

Chemical pesticides

One particular farmer uses metam sodium for soil fumigation once every two years i.e. the pesticide is applied after uprooting the old crop and before the new crop is planted. In this way the outbreak of soilborne pests has been minimized.

Mushroom compost

Mushroom compost, bought locally from mushroom growers, when added in the soil at the rate of 4-6 cubic metres / 1000m2 before planting, as a source of plant nutrients, was found to give effective control of soil pests, particularly weeds and plant diseases (two years experience by a strawberry grower). The compost is much cheaper than farmyard manure and gives better returns.

Mulch film

This has been found very useful for the control of insect vectors of viral diseases. However, at the moment, this approach is only available to the medium and large strawberry growers because the mulch film material is not locally available. The sample used for experimentation was imported from Israel.

III. MOROCCO

Protected crops

The following alternatives are used in protected crops:

2.1. Negative Pressure Soil Steam Sterilization (NPSSS);

2.2. Soil solarization in combination with fumigants (1,3 D, or metam sodium); and

2.3. Biofumigation.

2.1. Negative Pressure Steam Soil Sterilization (NPSSS)

In Farms dedicated to a very early production, plantation occurs in early August to produce and export in October. Soil preparations (cleaning from previous crop remains, plough, irrigations etc.) prior to soil disinfestation are required in June. Under these circumstances, the selected alternative has to take into account the short period available for soil disinfestation. To this end, steam sterilization is appropriate.

The performance of conventional sheet steaming is limited in sandy soils of Morocco. Appropriate temperatures (70°C) are obtained only in the first 10 - 20 cm of the soil profile. On the other hand, the Negative Pressure technique generates appropriate soil temperature at a 60 cm depth and complete control of nematodes, fungi and weeds is achieved. In this technique, the steam is introduced under the steaming sheath and forced to enter the soil profile by a negative pressure. The negative pressure is created by a fan that sucks the air out of the soil through buried perforated polypropylene pipes. This system requires a permanent installation of perforated pipes into the soil, at a depth of at least 60 cm to be protected from plough. To determine the exact time of treatment (which greatly determines the economic feasibility of the technique), the soil temperature has to be monitored at different levels during the treatment.

The technical advantage of the system is that the whole area to be occupied by the roots of the plants is effectively treated and protected from root-knot nematode re-infestations throughout the cropping cycle. Also, since the time to treat an area unit is much shorter compared to the conventional sheet steaming technique, the operational costs (fuel and water consumption) of NPSSS are much lower and are considered economic for the production of a very early produce. However, the technique needs an initial investment to install the negative pressure piping and the steam generators.

2.2. Soil solarization in combination with chemical fumigants

Under Moroccan conditions, fields tests carried out on soil solarization along the coastal area, during July - September 1982, 1987 and 1992, resulted in top-soil-layer temperatures above 50_C and 43 - 49°C at the first 10 - 20 cm of the soil profile and induced 60 % decrease in root-knot nematode populations. Under laboratory conditions, after a two-week exposure to 40°C, the infection potential of Meloidogyne javanica is completely eliminated, but hatching of eggs, although drastically affected, is not totally eliminated. Continuous hatching of eggs even under high soil temperatures permits early re-infestations which are originated from deep soil profiles with soil temperatures below 40°C and limits the effectiveness of solarization when applied alone. Because of these constraints which limit the effectiveness of solarization used alone, it was established as an effective practice and viable alternative to MeBr when applied as part of an IPM program.

Two chemical fumigants, with different properties (1,3-dichloropropene and metam sodium) were chosen to complement soil solarization. Metam sodium is applied to the soil using the existing (modified) drip irrigation system. A manifold of dripper pipes, spaced by 40 cm and each containing 4 l / h drippers spaced by 50 cm, is used. Drip irrigation system is already available in most of the farms and will need to be adapted for a safe chemical application, for a broadcast application (to avoid re-infestations) the irrigation lines will need to be doubled, a tank and a injection device is also needed. The application rate of metam sodium is about 5 l / m3 water, to apply 50 g / m2 soil, corresponding to 100 m3 water / ha and 500 l of metam sodium (1000 kg / ha of the 51 % formulation, which is registered in Morocco).

1,3-Dichloropropene will be applied using a special device for soil injection. After each treatment, the soil is immediately covered by clear polyethylene film, brought to the field capacity and left under solarization for 4 weeks instead of at least 6 weeks as required for a conventional solarization. Soil solarization combined with 1,3-Dichlorpropene is highly recommended where only root-knot nematodes are a major soil problem. Metam sodium is a poorer nematicide but in contrast is a good herbicide and fungicide.

2.3. Biofumigation

Bio-fumigation is often combined with the use of plastic tarps or other soil covers to raise soil temperature and to retain gases generated during the biofumigation process. In this way, the lethal effect of soil bio-fumigation on soilborne pests and diseases is caused by a combination of the direct effect of toxic substances from the decomposing bio-fumigants, and the long-term increase of soil temperature. Many soilborne organisms will be controlled and / or made more susceptible to hyper-parasitism by prolonged exposure to the sub-lethal temperatures obtained. Soil bio-fumigation need to be monitored to ensure that exothermic fermentation process is achieved and that appropriate temperature is reached and maintained over time. For an effective treatment, careful guidelines must be closely followed.

The soil must be well tilled to destroy clods and plant debris, which might interfere with uniform conduction of heat and bio-gases, and which might protect some organisms that could escape control. The bio-fumigant has to be chosen among available materials from the area (cost depend largely on availability and on transportation costs). Typically, an organic amendment partially decomposed with C : N ratio > 11 would be adequate. The dosage of bio-fumigant is variable ranging from 70 to 140 t / ha. It is recommended to place the bio-fumigation material in a layer at 10 to 20 cm from the soil surface, this layer is then covered with the soil, watered to start fermentation and usually covered with a plastic tarp. This technique needs a drip irrigation system installed under the tarp for an overall irrigation. To this end, the existing irrigation system will need to be modified and the irrigation lines will need to be doubled.

Soil bio-fumigation controls certain weed species, nematodes and a variety of soilborne diseases caused by fungi. This technique, when applied as part of an IPM program, is a viable alternative to MeBr.

Integrated Pest Management (IPM)

Basically the IPM programme includes:

Monitoring and identifying pests: IPM programmes work to monitor root-knot nematodes and identify them accurately, so that appropriate control decisions can be made in conjunction with action thresholds already established about 100 larva / 500 g of soil. This monitoring and identification removes the possibility that pesticides will be used when they are not really needed, or that the wrong kind of pesticide will be used.

Prevention: IPM programmes work to manage the crop to prevent pests from becoming a threat. This may mean using the right selected alternative with pest-resistant varieties, and planting pest-free rootstock. These control methods can be very effective and cost-effective and have little to no risk to people, or the environment.

Control: Once monitoring, identification, and action thresholds indicate that pest control is required and preventive methods are no longer effective, or available, IPM programs then evaluate the proper control method both for effectiveness and risk. The selected alternative is implemented . Also during the project, plastics will be recycled using the recycling factories available in the country, this recycling will also provide some extra savings to the farmer.

Therefore, the implementation of the IPM approach will require a well trained technical personnel in the field, able to assess the technical capabilities of farmers, farm infestation levels and, who has an adequate knowledge for environment to monitor pests and treatments.

Yield and performance of alternatives

The techniques alternative to MeBr were selected on the base of their technical and economic feasibility. They were tested during two cropping cycles (1998 - 1999 & 1999 - 2000) and included root-knot nematodes population dynamics (Table 1) and yield performance (Table 2). The integrated pest management programme included the determination of specific soil preparation practices aimed at maximizing the effectiveness of the proposed alternative.

After soil disinfestation during summer, prior to planting, the selected alternatives eliminated initial root-knot nematode populations and give similar results to MeBr. However,during the circle period following plantation, September - November, re-

Table 1. Effect of MeBr alternatives on root-knot nematodes (Meloidogyne javanica juveniles / 500 g of soil), during two crop seasons: 1998-1999 & 1999-2000

^aValues for June are before treatment and correspond to P0; Value for august corresponds to the nematode population after the treatment Pf.

infestation are relatively higher in soil treated with bio-fumigation and solarisation in combination with metam sodium compared to MeBr, solarization combined with 1,3-D and sheet steaming. Re-infestation during this period affect vigor, growth, flowering, fruiting and subsequently the quality and the quantity of the yield. Therefore any other action should occur during this period to maximize the efficacy of these alternatives.

During December - February, root-knot nematode populations drop naturally because the soil temperatures are below 20°C, and do not affect the yield. At the end of the production, the yield is already established and late infections affect the roots, but not the production. Statistically, yields differ significantly from the control, but not among the rest of the treatments including MeBr.

The IPM applied together with the alternative techniques included practices directed at enhancing nematode egg hatching, fungus spores, mycelia, or other conservation forms and to favor the germination of weed seeds, optimizing chemical diffusion, increasing and maintaining soil temperature during solarization, etc. As re-infestation and spread of nematodes and other soil borne diseases may occur by plant material and compost, or organic manure, the seedlings were carefully inspected and free of any infection (certified pest-free) and organic manure sterilized, or with composting process carefully monitor.

Table 2. Yield comparison for MeBr alternatives applied to tomato Daniela grafted on Beaufort

^aAs compared with the MeBr treated plots.

Acceptability to regulators and markets

The selected alternatives do not require any regulatory approval. The harvested vegetables are more acceptable to supermarkets and purchasing companies than those grown using MeBr, because solarization does not involve the use of toxic materials and reduces the companies' risk of criticism by consumers and the media.

Costs

Costs are basically estimated on labor involved (prior, during and after application of each selected alternative), the chemical, plastic, fuel and organic manure necessary to accomplish each alternative. Overall, solarization alone (bio-fumigation), or in combination with an application of metam sodium, or 1,3-D, is slightly more expensive compared to MeBr applied only to the planting beds at 350 kg / ha. However, the estimated cost for steam sterilization was low compared to MeBr. This cost includes only fuel and labor and does not include the investment for the steamer and the soil equipment for negative pressure. Economic studies based on local market and export values revealed the effectiveness of the selected alternatives as compared with MeBr.

Applicability to other regions

Negative Pressure steam sterilization is an environmentally safe and sustainable technology in soil disinfestation. It was basically developed as an alternative to MeBr in Holland and also in Syria. Its application is highly recommended in sandy soils. Solarization alone, or bio-fumigation as presented in this report is being used with success in Mediterranean climate during at least 6 - 8 weeks to control rot knot nematodes. Solarization in combination with metam sodium, or 1,3 dichloropropene, could be applied wherever solarization alone is possible, but under severe root-knot infestations and where the cropping cycle, and the climatic and soil conditions enhance the multiplication of nematodes.

Table 3. Compared cost estimates in $US of methyl bromide and selected alternatives for tomato

^a 70 tons of organic manure (90 tons) and soil solarization during 6-8 weeks.

^bSoil solarization combined with metam sodium (1000 l / ha) applied in drip irrigation during 4 weeks.

^cSoil solarization combined with 1,3 dichlororpropene (400 l / ha) injected at 25 cm soil depth, for 4 weeks.

^dSoil sterilization using either sheet steaming, or negative pressure technique.

BIBLIOGRAPHY

Ammati, M. 1998. Alternatives to methyl bromide in soil fumigation of tomato production in Morocco. In: Regional workshop on methyl bromide alternatives for North Africa and Middle East; UNEP IE; Rome, pp. 26-29.

Chellemi D. O., Rich, J. R., Barber, S., McSorley, R. and Olson, S. M. 1997. Adaptation of soil solarization to the integrated management of soilborne pest of tomato under humid conditions. Phytopathology, 250-258.

Katan J and DeVay JE 1991. Soil Solarization CRC Press, Boca Raton, Florida.

KFC, 1999. Pesticide toxicological ratings update 1st June 1999. KFC Code of Practice, Edition 4 January 1999.

Klijnstra, J. W. 1999. Background paper on methyl bromide issues related to Eastern and Southern Africa. In: Proc. workshop on methyl bromide alternatives in Eastern and Southern Africa, Malawi, 7-10 September 1999.

Malins, A.; Blowfield, M. and Dolan, C. 1998. Kenya Flower Council, Support to enhancement of Social and Enviromental Practices: Report of the Design Mission. NRET Programme, Institute of Developmental Studies, NRI: Draft Report, December 1998

Mungai, K. 1995. Strawberry farming. Horticultural News, November / December 1995, 19.

Patel, V. 1999. Growing of cut flowers without methyl bromide. In: Proc. workshop on methyl bromide alternatives in Eastern and Southern Africa, Malawi, 7-10 September 1999.

Schonfield, A., Wamukonya , L. and Glendening, S. 1994. Methyl bromide use and alternatives in Africa. Review draft, Pesticide Action Network, October 1994.

¹ The alternatives described herein refer especially to large and medium-size farms.