Alternatives to methyl bromide for the control of weeds in greenhouses and seed beds




Дата канвертавання18.04.2016
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ALTERNATIVES TO METHYL BROMIDE FOR THE CONTROL OF WEEDS IN GREENHOUSES AND SEED BEDS

I.G. Eleftherohorinos and K.N. Giannopolitis

Lab. of Agronomy, School of Agriculture, Aristotle University of Thessaloniki, Greece and Weed Science Department, Benaki Phytopathological Institute, Athens, Greece
Methyl bromide, the most effective soil fumigant applied against nematodes, insects and diseases, is also effective against a broad spectrum of annual and perennial weeds. Results published in the literature and results from our survey conducted recently in greenhouses of Northern Greece, where methyl bromide has been used for several years, indicate excellent efficacy against the annuals Abutilon, Amaranthus, Avena, Chenopodium, Conyza, Datura, Digitaria, Echinochloa, Galinsoga, Papaver, Poa, Portulaca, Setaria, Solanum, Stellaria and Urtica, and very good efficacy against the perennials Sorghum, Cynodon, Cyperus and Convolvulus.

Since methyl bromide is going to be phased out by 2005, mainly because of its detrimental effect on the ozone layer, research is urgently needed on alternative methods to be used in vegetable and other crops grown in greenhouses and for seed beds, where this chemical is mostly used. Soil application for metham sodium or dazomet and soil solarisation (alone or in combination with chemicals) are among the most likely substitutes to methyl bromide and this is the reason why most of the research has been focused on these methods.

Metham sodium has a good efficacy against the annuals Alopecurus, Digitaria, Echinochloa, Poa Amaranthus, Chenopodium, Lamium, Portulaca, Stellaria, and against the perennials Taraxacum, Convolvulus, Cynodon and Sorghum.

Dazomet controls effectively the annuals Amaranthus, Bilderdykia, Chenopodium, Digitaria, Portulaca, Sinapis, Striga and the perennials Convolvulus, Cynodon and Sorghum.

However, these two chemicals are expected to be less acceptable by the growers as they have a number of serious disadvantages compared to methyl bromide: 1) they must be applied in large quantities which are difficult to handle, 2) they depend on irrigation for their activation after they have been applied, 3) they have a reduced effectiveness against some common weeds (Solanum and Cyperus), 4) they are readily leached which increases the potential for groundwater contamination, 5) they have a short residual activity which means a short lasting weed control efficacy.

Solarisation is very effective against a wide spectrum of weeds, with the exception of the annuals Avena sterilis, Amaranthus retroflexus, Portulaca oleraea, Xanthium strumarium, and of the perennials Convolvulus, Cynodon and Sorghum.

However these two chemicals are expected to be less acceptable by the growers as they have a number of serious disadvantages compared to methyl bromide:

1) they must be applied in large quantities which are difficult to handle, 2)they depend on irrigation for their activation after they have been applied, 3) they have a reduced effectiveness against some common weed (Solanum and Cyperus), 4) they are readily leached which increases the potential for groundwater contamination, 5)they have a short residual activity which means a short lasting weed control efficacy.



Solarisation is very effective against a wide spectrum of weeds, with the exception of the annuals Avena sterilis, Amaranthus retroflexus, Portulaca oleracea, Xanthium strumarium, and of the perennials Convolvulus arvensis, Cynodon Dactylon, Cyperus spp. and Sorghum halepense. The reduced effectiveness of this method and the fact that soil cannot be used for cropping for at least two months are the two main disadvantages of this method.

In the case of weeds, therefore, successful replacement of methyl bromide with currently available alternative methods seems rather difficult. Its phasing out will certainly make weed control in green houses and seed beds much more difficult and weeds will probably become one of the most serious problems for greenhouse growers in the coming years.


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