Summary. The use of methly bromide in Italy is extremely high, ranking second in the world. This is especially due to the importance of the Italian horticultural sector, which is characterized by intensive cultivation of high value crops without rotation. Alternatives to the use of MeBr for soil fumigation are being increasingly used and others are being developed, in order to meet the deadlines for MeBr phase-out. Especially the use of steam, soil solarization, chemical alternatives and their combinations, as well as combinations of cultural practices, physical methods and chemicals, provide effective control of soil pests.
Key words: intensive cultivation, fungi, methyl bromide, steam, chemical alternatives
Italian horticulture is characterized by intensive cultivation systems, highly specialized and usually of small size, where the high plant density and the repeated planting of the same crop, practice very common in the case of valuable crops, cause a build-up of detrimental biological factors in the soil. The aggressiveness and rate of accumulation of different pathogens in the soil depends upon factors such as host susceptibility to pathogens, cropping history, physical and biological properties of the soil, cultural practices, climate, control measures and field hygiene.
Soil disinfestation is usually carried out in the case of protected vegetable and ornamental crops of high value and sometimes also in the open field (Katan, 1984; Garibaldi and Gullino, 1995; Gullino and Garibaldi, 1995). The main goal of soil disinfestation is to eliminate, or simply control, major soilborne plant pathogens and pests, usually before planting. In particularl in the Italian vegetable and ornamental sectors, fungi represent the most important pathogens to be controlled. A non-comprehensive list of the major fungal pathogens of vegetable and ornamental crops in Italy is presented in Table 1.
From a technical point of view, soil disinfestation should be economically feasible. Under these perspectives, fumigants are often the method of choice, due to their relative low cost and broad spectrum of activity. Certain physical and chemical characteristics of MeBr amde this fumigant the most widely used in Italy against soilborne pathogens. MeBr has a broad spectrum of activity, quick and deep penetration into the soil; very short exposure period; fast dissipation from the soil after fumigation; penetration into undecomposed material; increased Growth Response effect; good efficacy in a wide range of temperatures; efficacy with more than one
Table 1. Main fungal pathogens of vegetable and ornamental crops in Italy
PATHOGEN |
HOST PLANT |
Fusarium oxysporum f. sp. melonis |
melon |
Fusarium oxysporum f. sp. cucumerinum |
cucumber |
Fusarium oxysporum f. sp basilici |
basil |
Fusarium oxysporum f. sp niveum |
watermelon |
Fusarium oxysporum f. sp. cyclaminis |
cyclamen |
Fusarium oxysporum f. sp. dianthi |
carnation |
Fusarium oxysporum f. sp. lycopersici |
tomatoes |
Fusarium solani f. sp. Cucurbitae |
cucurbits |
Fusarium solani f. sp. Phaseoli |
beans |
Fusarium tabacinum |
basil |
Phytophthora capsici |
peppers, tomatoes, eggplants cucurbits |
Phytophthora cactorum |
strawberries |
Phytophthora cryptogea |
gerbera |
Phytophthora fragariae |
strawberries |
Phytophthora parasitica |
carnations, tomatoes and other species |
Pyrenochaeta lycopersici |
tomatoes |
Pythium ultimum |
different species in seedbeds |
Rhizoctonia solani |
lettuce, beans, basil carnations, artichokes and other plants in seedbeds |
Sclerotinia sclerotiorum |
lettuce, cucurbits basil artichokes, beans and other plants in seedbeds |
Thielaviopsis basicola |
several vegetable and ornamental species |
Verticillium dahliae |
tomatoes, eggplants, strawberries, cucurbits, artichokes, rose and gerbera |
crop. Italy ranks second in the world, together with Japan, and first in Europe for consumption of MeBr, due to the importance of its horticultural sector (Gullino and Clini, 1998).
Recently, the restrictions on the use of MeBr because of ozone depletion, have set an interesting scientific, technical and political debate. A high degree of cooperation between the scientific, technical and political sectors is required, if viable solutions are to be in place for many uses, by the time MeBr is withdrawn (Gullino and Clini, 1999). No single "plug-in" replacement for MeBr appears to exist. At present, it is possible to distinguish two main categories of alternatives:
II. ALTERNATIVES CURRENTLY USED IN ITALY
In this section, the technologies alternative to the use of MeBr for soil disinfestation currently used in Italy are briefly described, with special emphasis on their positive features and constraints encountered in their implementation under the Italian cultural and environmental conditions.
Cultural practices
In the development of new alternatives to replace MeBr, the natural approach is to check the latest technological advances and investigate the ways to implement these new systems or control practices. There is also some merit, however, in looking back and reviewing the situation which existed before MeBr was introduced (Matta, 1988). Crop rotation is one of the best examples, as it confirms to be extremely helpful in controlling the spread of many soil-borne pathogens (Palti, 1981). A significant commitment to applied research and technology transfer programmes will still be necessary to take full advantage of the potential of cultural practices in the many different agricultural situations.
Resistant varieties
Varieties, which are resistant, or tolerant to one, or few, specific pathogens (and races) are already available for many crops. Resistant hybrids with multiple resistance to several pathogens exist and are currently used in vegetable production (Cirulli, 1988; Laterrot, 1991). In most cases new varieties are developed through plant breeding techniques to address specific pest problems, but systematic genetic modification of germplasm by using new biotechnologies is becoming more frequent.
Positive features
Constraints
Soilless cultivation
Soilless cultivation is rapidly expanding also in Italy, although slowly in comparison with Northern Europe. This technique may bridge unusual production periods and circumstances, and may also serve as an answer to the need of reducing the use of soil fumigants. Soilless cultivation represents an interesting alternative to the traditional agricultural systems for high value crops such as rose, carnation, gerbera, basil, lettuce, etc. (Serra, 1994; Tognoni and Serra, 1994). The phytopathological problems of soilless cultivation systems have been recently reviewed (Gullino and Garibaldi, 1994; Stanghellini and Rasmussen, 1994). The choice of the most suitable soilless cultivation system for a given environment relies on technical, economical and phytopathological factors.
Soilless cultivation is increasingly adopted in Italy in the case of ornamental crops (rose, gerbera) and, in very limited situations, in northern Italy for strawberry. A total of approximately 100 ha is at present cultivated soilless in Italy. It must be noted that all the soilless systems adopted in Italy are open, thus without recirculation of the nutrient solution.
Positive features
Constraints
Crop rotation
It is particularly difficult to apply crop rotation in intensive vegetable and ornamental crop systems and for this reason it is not common in Italy as an alternative to MeBr.
In practice, in Italy, the following rotations can be used:
Positive features
Constraints
limited availability of alternative crops suitable not only as a non-host crop but also from an economic point of view.
Physical methods
There are two different physical approaches to soil disinfestation: steaming and soil solarization. (Katan, 1984; Gullino and Garibaldi, 1995).
Steam
In Italy, steam is almost exclusively applied in the case of high value greenhouse crops (Gullino and Garibaldi, 1995). However, new application technologies are under development, which might significantly reduce the costs of such method. At present it is adopted only in the case of ornamental crops (rose, gerbera), or for high value vegetables (i.e. basil), due to its high cost. In Italy, steaming is carried out by adopting the most traditional technique of sheet steaming. Sheets are smoothed out over the soil and enclosed at the edges; steam is then blown under the sheets and left to penetrate the soil.
Positive features
Constraints
Soil solarization
Southern Italy provides excellent conditions for implementation of soil solarization (Cartia, 1989). However, despite the fact that incentives to the implementation of soil solarization have been attempted in the past (i.e. free plastic for soil mulching in the Liguria Region; plastic recycling in Sicily), soil solarization is rarely adopted in practice in Italy. At present a maximum of 50 ha are solarized, especially in southern Italy (Campania and Sicily Regions). Bench solarization and solarization in greenhouses are new applications of this technique that may help its spreading even in marginal climatic areas (i.e. North-Central Italy) and seasons (Garibaldi and Gullino, 1991).
Positive features
Constraints
Methyl isothiocyanate (MITC) and its generators
Metam sodium is a liquid soil chemical, effective for controlling arthropods, some weeds and soilborne pathogens, principally fungi, and a limited number of parasitic nematode species. It is applied to the soil by direct injection, or through the irrigation system. Metam sodium must be applied when soil temperatures are between 15 and 30°C. The application rate is 100 ml / m2 (with formulations at 32,7 % of a.i.). At high inoculum concentrations, low soil temperatures, or for heavy soils it is necessary to increase the rate up to 800 ml / m2.
Dazomet is a granular pre-planting soil chemical and has been reported to control weeds, nematodes and fungi. It requires mechanical distribution in the soil for good movement and efficacy. During the treatment the soil should be covered with plastic sheets. The application rate is 80-100 g / m2 (with formulations at 99 % of p.a.).
Positive features
Constraints
1,3 dichloropropene (1,3-D)
Liquid 1,3-D, applied to the soil by injection, provides effective control of nematodes, insects, some weeds and some pathogenic fungi. During treatment the soil remains covered with plastic mulches.
1,3-D is usually applied in combination with other chemicals such as chloropicrin, metam sodium, etc. Application rate is 12-20 ml / m2 (with formulations at 97 % of p.a.); higher rate are applied to heavy soils.
Positive features
Constraints
Chloropicrin
It is worth mentioning Chloropicrin, although still forbidden in Italy (because still registered as a war gas), since it is also a valid option. Presently under registration in Italy, it controls most soilborne fungi, root destroying insects and other organisms such as slugs, snails and earwigs.
Since new fumigants with a broad spectrum of activity and of low environmental impact have not been developed, yet, growers are forced to use old compounds. In Italy, recent data made available by Agrofarma, showed an increase in fumigant usage in 1998 of 11 % in value and 16 % in quantity (Anonymous, 1999).
Combinations of chemical and non-chemical alternatives, notably soil solarization, led to encouraging results: examples include metam sodium, dazomet, or 1,3-D + chloropicrin in combination with solarization, or gas impermeable plastic mulches. Studies are being conducted to evaluate additional combinations and to optimize ratios of chemicals and improved methods of application.
Particularly interesting appears the possibility of applying fumigants such as metam-sodium and dazomet under plastic. Covering the soil with low-density polyethylene (LDPE) film allowed to use a half dose of the fumigants, with generally good results, both under greenhouse and field conditions. Moreover, such practices reduced the emission of unpleasant smells, particularly in the vicinity of houses (Gullino et al., 1998: Minuto et al, 2000).
Also the combination of two weeks of soil solarization with half dose of fumigants proved to be effective in most cases and allowed a shortening of solarization, permitting a reduction in the non cultivation period. Such a combination was effective on subsequent crops, thus confirming the long term effect described for soil solarization (Katan and DeVay, 1991). The possibility of combining soil solarization with reduced dosages of fumigants could indeed increase the number of growers using solarization as a disinfestation method, helping to reduce the present dependance on chemicals. It must be stressed that the usage of half dose of fumigant in combination with a shorter period of solarization remains essential, at present, in order to achieve an acceptable level of disesase control, especially in the case of high value protected crops (Gullino, 1998). In Table 2, alternative technologies in Italy are summarized, presenting them on a feasibility and applicability degree basis.
The efficacy, availability of simple application systems and technology, together with the broad spectrum of activity and relatively low cost, make MeBr extremely difficult to replace. Furthermore, many of the options are not yet at a stage where they could be used extensively without considerable increase of costs.
The appropriateness of a given alternative, or combination of alternatives, is dependent on a variety of factors, including social infrastructures, climate, market, presence of pathogens, land availability, soil type and conditions. The complex interactions among these factors require the choice of the best alternatives on a case-by-case basis. Nevertheless, there are some practices which have widespread applicability, though not necessarily producing the same yield and having the same profitability as MeBr, and which may need local optimization to perform to their full potential. For instance, alternatives that have been developed in cold climate and then transferred to warmer regions, or vice-versa.
Furthermore, to successfully replace MeBr use, many of the alternative processes identified must be used in combinations. For soil treatment, there is wide agreement that IPM systems are needed to replace MeBr-based strategies, since no single alternative is currently, or likely to become, available. Site-specific IPM treatment programmes combine two, or more, methods selected among biological, cultural, physical, mechanical and chemical methods (Albajes et al., 1999). Some alternatives have a limited spectrum of activity, thus some combinations and / or rotations with different alternatives may achieve broad spectrum pest control and yields approaching, or exceeding, those obtained with MeBr.
On a longer range, since the few available chemical alternatives to MeBr (i.e. metam sodium and dazomet) will be widely applied, their safe application is essential to obtain a satisfactory level of disease control, without causing negative environmental side-effects. In this perspective, it is crucial to exploit to the utmost the few available fumigants and to use application technologies which permit their dosages to be reduced while retaining their activity.
The higher costs and the fear of loss of reliability represent among the growers the major limits to the wide-spread of the most promising alternatives to the use of MeBr already available. Moreover, many countries cannot depend on an efficient extension service web which helps growers to switch from MeBr to other new techniques.
From the results of a survey carried out by Di.Va.P.R.A. (Dipartimento di Valorizzazione e Protezione delle Risorse Agroforestali, Turin University, Italy) with the help of technicians belonging to the "Servizi Fitosanitari" and the Growers Associations (Gullino et al., 1998), the lack of know-how and information appears as the main reason for growers' lack of confidence.
A strong action is needed, in order to make sure that alternatives to MeBr will be applied with a long term perspective, based on a sustainable view of agriculture. Extension service people and other operators of the sector are thus called to provide the adequate support to growers in order to help them to switch from MeBr to other alternative methods. The fragmentary and diversified reality of the Italian agriculture makes this task even more difficult.
In conclusion, the diffusion of the scientific results plays an essential role in the process of transfer into practice of the new techniques of soil disinfestation. Only a global, coordinate approach, involving all actors (growers, researchers, fumigators, technicians, etc.) will allow to switch smoothly from MeBr to its alternatives.
Table 2. Technical evaluation of the degree of development, the transferability into practice and the efficacy of alternative technologies to the use of MeBr as soil fumigant
EFFICACY |
||||||||
Treatments |
Degree of development1 |
Transferability into practice2- |
spectrum of activity |
climatic dependence |
||||
|
|
|
|
specific |
broad |
low |
high | ||
4 |
100 |
|
< |
< |
| |||
non-chemical methods |
|
|
|
|
|
| ||
Agricultural practices |
|
|
|
|
|
| ||
Crop rotation |
4 |
75 |
|
< |
< |
| ||
Resistant varieties |
4 |
75 |
< |
|
< |
| ||
Grafting |
2 |
60 |
|
< |
< |
| ||
Soil amendments and biofumigation |
2 |
60 |
< |
|
< |
| ||
Soilless cultivation systems |
2-3 |
60 |
|
< |
< |
| ||
Physical control |
|
|
|
|
|
| ||
Steam |
4 |
100 |
|
< |
< |
| ||
Soil solarization |
3 |
75 |
|
< |
|
< | ||
Biological control |
2 |
50 |
< |
|
|
< | ||
Chemical methods |
|
|
|
|
|
| ||
Metam sodium |
4 |
90 |
|
< |
|
< | ||
Dazomet |
4 |
90 |
|
< |
|
< | ||
1,3-D |
4 |
90 |
< |
|
|
< | ||
Chloropicrin 3 |
1 |
50 |
4 |
|
4 |
|||
2 1 = at experimental stage in the laboratory; 2 = at
experimental stage in the field; 3 = at small scale; 4 = at commercial
scale.
2Feasibility: from 0 to 100: 0 = degree of feasibility in the Italian
agricultural reality (100 = extremely high feasibility).
3Under registration in Italy.
Albajes R., Gullino M. L., Van Lenteren J. C. and Elad Y. 1999. Integrated pest and diseases management in greenhouse crops. Kluwer Academic Publishers, Dordrecht, The Netherlands, 545 pages.
Anonymous, 1999. Assemblea generale Agrofarma 1999. Rapporto 1998-1999. 24 pages.
Cartia G. 1989. La solarizzazione del terreno: esperienze maturate in Sicilia. Informatore Fitopatologico, 39 (5), 49-52.
Cirulli M. 1988. Le resistenze genetiche nel controllo biologico delle malattie delle piante ortensi. Informatore Fitopatologico, 38, 19-20.
Garibaldi A. and Gullino M. L. 1991. Soil solarization in southern European countries, with emphasis on soilborne disease control of protected crops. In: Soil solarization (Katan J., De Vay J.E. eds), CRC Press, Boca Raton, USA, 227-235.
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Gullino M. L., Minuto A. and Gasparrini G. 1998. Bromuro di metile: la parola agli agricoltori. Colture Protette, 27 (7), 39-42.
Gullino M. L., Minuto A., Minuto G. and Garibaldi A. 1998. Chemical and physical alternatives to methyl bromide and their combination in the control of Rhizoctonia solani and Sclerotinia sclerotiorum in the open field. Proc. Brighton Crop Protection Conference, 693-700.
Gullino M.L., Minuto A. and Garibaldi A. 1998. Improved method of bench solarization for the control of soilborne diseases of basil. Crop Protection, 17, 496 - 501.
Gullino M. L. and Clini C. 1999. Alternatives to methyl bromide for soil disinfestation: results, problems and perspectves. The Italian view. Proc. Earth Technologies Forum, Washington DC, September 27-29, 1999, 54-56.
Katan J. 1984. The role of soil disinfestation in achieving high production in horticulture crops. Proc. Brighton Crop Protection Conference, 3, 1189-1193.
Katan J. and DeVay J. E. 1991. Soil solarization, CRC Press, Boca Raton, USA, 267 pp.
Laterrot H. 1991. Lutte génétique contre les parasites des cultures maraicheres sous abris. Phytoma, 428, 41 - 45.
Minuto A., Gilardi G., Gullino M.L. and Garibaldi A. 1999. Reduced dosages of methyl bromide applied under gas-impermeable plastic films for controlling soilborne pathogens of vegetable crops. Crop Protection, 18, 365-371.
Minuto A., Gilardi G., Pomè A., Garibaldi A. and Gullino M.L. 2000. Chemical and physical alternatves to methyl bromide for soil disinfestation: results against soilborne diseases of protected vegetables cop. Journal of Plant Pathology, in press.
Palti J. 1981. Cultural practices and infectious crop diseases. Springler-Verlag, Berlino, 243 pages.
Serra G. 1994. Innovation in cultivation techniques of greenhouse ornamentals with particular regard to low energy input and pollution reduction. Acta Horticulturae, 353, 149-163.
Stanghellini M. E. and Rasmussen S. L. 1994. Hydroponics. A solution for zoosporic plant pathogens. Plant Disease, 78, 1129-1138.
Tognoni F. and Serra G. 1994. New technologies for protected cultivations to face environmental constraints and to meet consumer's requirements. Acta Horticulturae, 361, 31-38.
1 Several soil disinfestation techniques (fumigants, steam, etc.) reduce not only the pathogens, but also the beneficial fauna and flora naturally present in the soil ("biological vacuum"). In such conditions, soil can be easily re-colonized by all kind of pathogens, even those usually considered of minor importance ("boomerang effect"). Re-infestation takes place through the irrigation water, infected soil particles, or crop debris, etc.
