Alternatives to Methyl Bromide for the Southern European Countries
Heraklion, Greece, 7-10 December 1999
Towards the Development of Sustainable Alternatives to Methyl Bromide for the Control of Green House
Tomato Soil-Borne Pathogens in a Developing Country: Morocco
Mohamed Besri
Institut Agronomique et Vétérinaire Hassan II, Rabat, Morocco
E-mail: besri@acdim.net.ma
Summary
Tomato is attacked by many soil-borne pathogens which are used to be controlled by Methyl Bromide. To decrease
the use of Methyl Bromide, some integrated pest management programs (IPM) based mainly on local research
results, were developed and implemented in some tomato green house and in close collaboration with farmers who
are producing this crop for export. These tomato farmers are highly technically advanced and on the watch of any
new technology regardless of its cost . They are also aware of the Methyl Bromide problem and try to prepare
themselves to the moment when this important powerful ozone depleting compound will be phased out .
I- Economic importance of vegetable crops in Morocco
In general, vegetable crops and particularly tomatoes generate about 90 millions working days. This number
represents 22 % of all the agricultural manpower employed by the Moroccan agriculture. In addition, vegetables
crops provides 3 millions working days in packing houses and caning industry. The exported crops sector employs
about 500,000 persons and nourish 3 millions people ( 1 person is responsible of an average family of 6) which
represents 10.7 % of the Moroccan population. A survey conducted in 1991-1992 has shown that 21% of the food
expenses are for the purchase of vegetable commodities
The horticultural sector is a very developed one. It plays an important role in the modernisation of the Moroccan
agriculture and also in encouraging and financing research activities. Most of the new agricultural technologies were
developed or introduced in the country because of the horticultural demand ( green-houses, drip irrigation, soil
fumigation, new hybrids and varieties, grafting, etc..). Some of these new technologies are then adapted and adopted
by other crops.
In 1997-1998, Morocco has exported about 299,000 T of vegetables, 69 % of this volume is represented by tomatoes
(Table 1). Vegetables are mainly exported to France (74 %), other European Union countries (8 % ) , Russia (6%)
and other countries such as USA, Canada, Poland, etc..(10 %).
Table 1
Acreage (ha), production and export (T) of early vegetables in 1996-1997 and 1997-1998
Crop
Surface (Ha)
Production (T)
Export (T)
96-97
97-98
96-97
97-98
96-97
97-98
Tomato
a)
3,700
3,600
410,000
461,000
150,730
207,070
b)
1,500
1,500
80,00
79,000
14,820
13,440
Potato
10,000
9,500
127,000
135,000
50,530
28,180
Others
5,300
4,900
158,000
180,000
40,920
50,310
Total
20,500
19,500
775,000
855,000
257,000
299,000
a): Green-house tomato
b): Open field Tomato
II- Methyl Bromide use on soils and consumption
The attitude that Methyl Bromide is the universal panacea to control soil-borne pathogens, nematodes and weeds is
still prevailing among many protected crops growers. For soil fumigation , Methyl Bromide is used in combination
with chloropicrin (respectively 98% and 2%). Chloropicrin is used as a detector because Methyl Bromide is an
odorless gas.
Methyl Bromide use on soils is related to export crops grown under plastic cover (except banana which is grown
only for the local market). Tomato represents 57.85% of the total area fumigated by this chemical (Table 2 ). The
utilization rate varies from 750 kg \ ha to 1000 kg \ ha
Table 2
Importance of Methyl Bromide used for soil disinfection in the most important covered crops (1996)
Crop
Area fumigated (%)
Tomato
57.85
Melon
13.66
Strawberry
10.96
Banana
6.78
Others
10.75
In 1998, the volume of Methyl Bromide used for vegetable soil disinfection was about 1,220 T.
The soil disinfection cost with Methyl Bromide is very low and represents only 2.03 % of the total cost. The low
price, the low part of the product in the total investment and also the high efficacy of Methyl Bromide to control soil
borne pests explain why this fumigant is very popular and is widely used in vegetables covered cultivation. Tomato
is grown under cover from July till May. The farmer has only one to two months to prepare the next crop
Therefore, preplant application of the fumigant permits the soil to be replanted within a short waiting period. The
chemical, applied by specialized companies, is injected into the soil, which is covered by a plastic tarp to contain the
pesticide. For vegetables and strawberries, only the plant rows are fumigated. The tarps are then used as mulch for
the plant and are removed at the end of the season. For bananas, all the surface of the greenhouse soil is fumigated.
In this case, when the fumigation is complete, the tarps are removed from the field. Therefore, the release of Methyl
Bromide into the atmosphere is higher after the fumigation of the banana soils than after the fumigation of the
vegetables ones.
III- Alternatives to Methyl Bromide
Tomato is attacked by many soil-borne pathogens, some of them such as, Didymella lycopersici (Didymella stem
rot), Clavibacter michiganense (bacterial canker) , Pseudomonas syringae p.v tomato (bacterial speck), Orobanche
(Orobanche crenata) are easily controlled by the farmers without Methyl Bromide. However, the key soil-borne
diseases, Fusarium (Fusarium oxysporum) and Verticillium (Verticillium dahliae) wilts, root knot nematodes
(Meloidogyne spp.) are used to be controlled by Methyl Bromide. These pathogens are particularly severe in sandy
soils such as in the most important vegetables growing region of the country, the region of Agadir. To decrease the
use of Methyl Bromide, an integrated pest management program (IPM) based mainly on local research results
obtained by the department of plant pathology of the Hassan II Institute of Agronomy and Veterinary Medicine
(Rabat, Morocco), since 1972, was implemented in some farms and in close collaboration with farmers who are
aware of the Methyl Bromide problem and who are preparing themselves to the moment when this chemical will be
phased out. The IPM program integrates all the suitable alternatives in compatible ways to maintain the key soil pest
populations at levels below the economic threshold level.
A- Alternatives to Methyl Bromide for the control of Fusarium and Verticillium wilts:
Most of the cultivars available in the Moroccan market are resistant to the two diseases. The most popular cultivars
in the country , Daniella and Gabriella , have a high level of resistance to these two pathogens. In addition, the use
of some non chemical control methods such as sanitation, crop rotation with pepper or hot pepper , which are not
infected by the two pathogens (V.dahliae has never been observed in Morocco on pepper grown under cover) ,
certified seeds, use of non saline water (the saline water increases the plant susceptibility to the two pathogens and
breaks down the resistance of the resistant cultivars) and weed control (weeds are host of Fusarium and
Verticillium).
B- Alternatives to Methyl Bromide for the control of root knot nematodes :
In the Moroccan conditions, and particularly in the sandy soils, Meloidogyne spp are the most important pathogens
of tomato. Methyl Bromide is mainly used for the control of these pathogens. The most popular tomato cultivars are
Daniella and Gabriella. The alternatives to be used varies according to the cultivar.
Daniella :
Daniella, was two years ago, the most popular cultivar for its firmness , high vigor, shelf life , tolerance to salinity
and low temperatures This cultivar is resistant to Tobacco Mosaic Virus and to Fusarium and Verticillium wilts.
Unfortunately, the cultivar is very susceptible to nematodes, particularly in sandy soils. However, with the adoption
of the same cultural practices as those previously reported for Fusarium and Verticillium wilts, grafting on resistant
rootstocks and soil disinfection with Metam Sodium through the drip irrigation system, this cultivar continues to be
grown without Methyl Bromide.
Grafting, which was considered at one time too expensive, is now widely used in Morocco at a commercial level . In
general, without grafting, the tomato plant population per ha is about 18,000. When grafted plants are used, it has
been shown that the same yield could be obtained with half plant population (9,000 plants/ha). The grafted plants are
conducted with two stems instead of one for the non grafted plants.
Gabriella:
Gabriella is a cultivar newly introduced into the country. Experiments in the local conditions have shown that this
cultivar has the same horticultural characteristics as Daniella. This cultivar is also resistant to the same pathogens as
Daniella. In addition, it is resistant to nematodes. However, this resistance is broken down with high temperatures,
as it is the case in Morocco. Therefore, this cultivar could not be grown without soil disinfection . It has been shown
that Metam Sodium, applied through the drip irrigation system, is the best fumigant to be used as alternative to
Methyl Bromide. These two fumigants have the same price. The seed price of Gabriella is also similar to the
Daniella. Therefore, there is no extra cost when using this cultivar instead of Daniella.
Conclusion
In Morocco, alternatives to Methyl Bromide for tomato production are available. These alternatives developed to
control the key pest diseases (Fusarium and Verticillium wilts and root knot nematodes) , according to the cultivar
grown , are adopted by some farmers .These farmers who are producing tomato for export , are technically more
developed and are also on the watch of any new technology regardless of its cost. The proposed alternatives for the
Agadir area are integrated in an IPM program:
 use of the cultivar Gabriella or Daniella grafted on resistant rootstocks.
 soil fumigation with Metam Sodium applied through the drip irrigation system,
 crop rotation including exported crops in various combinations according to the export market: tomato- squashbeans -melon- hot pepper, or tomato-beans-melon-hot pepper-squash , or tomato-melon- hot pepper- beanssquash . It is important that the following crop should not belong to the same family as the previous one. Hot
pepper could be replaced by pepper.

Other cultural practices such as sanitation, organic amendments , pathogens free seeds and seedlings, weed
control, and improvement of plant growing conditions,
This IPM program can be adapted for other regions which have similar conditions (pathogens populations, cultural
practices and environment ).
Some tomato cvultivars used at the moment such as Gabriella are resistant or tolerant to the key existing soil-borne
pathogens (F.oxysporum f.sp.lycopersici race1 and 2, V.dahliae race 1 and Meloidogyne spp.) . However, the market
needs, the cultural practices and also the soil-borne pathogen populations could change in the future as it was the
case in many countries. At the moment, no tomato variety is resistant to some other tomato soil-borne pathogens
such as Verticillium race 2, Fusarium race3, Fusarium oxysporum radicis - lycopersicisi and Pyrenochaeta
lycopersici . Therefore, more research should be conducted in order to develop new alternatives to Methyl Bromide
integrated in new IPM programs. Demonstration projects and training courses for the farmer should also be
developed and organised.
Selected references
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