twistedwords
Well-Known Member
http://www.fao.org/docrep/v9978e/v9978e08.htm
Chemical control of nematodes
The demand
The elimination of nematodes from some crops is essential for certain export requirements, particularly of high-value horticultural products. Chemical treatment with fumigants or nematicides may be the only technique available, and from the plant quarantine standpoint it is important that their use is retained.
The use of chemicals in protected cropping may still be preferable to other techniques such as steam treatment for economic and practical reasons. The use of soil-less growing media in some north European countries has resulted in a decreased demand for chemical treatments. In southern Europe, the Mediterranean region and North Africa, many horticultural and salad crops are grown in soil under polythene and soil treatment with methyl bromide, dazomet or non-fumigant nematicides is widely practised. The cost of such treatments may be as much as US$500 per hectare per year and can only be justified if the crops are of high market value.
Efficacy
Fumigants. Several general purpose fumigants give excellent control of nematodes in soil. The efficacy is related to their high volatility at ambient temperatures. All fumigants have low molecular weights and occur as gases or liquids. As they volatilize, the gas diffuses through the spaces between soil particles; nematodes living in these spaces are killed.
TABLE 1
Nematicides currently available on world markets
Chemical name
Trade name
Formulation
Fumigants
Methyl bromide
Dowfume
Gas
1,3 dichloropropene
Telone/DD-95
Liquid
Ethylene dibromide1
Dowfume W-85
Liquid
Metam-sodium
Vapam
Liquid
Dazomet
Basamid
Dust (prill)
Methyl isothiocyanate
Di-Trapex
Liquid
Chloropicrin1
Larvacide
Liquid
Organophosphates
Thionazin
Nemafos
Granular or emulsifiable liquid
Ethoprophos
Mocap
Granular or emulsifiable liquid
Fenamiphos
Nemacur
Granular or emulsifiable liquid
Fensulfothion
Dasanit
Granular
Terbufos
Counter
Granular
Isazofos
Miral
Granular or emulsifiable liquid
Ebufos
Rugby
Granular or emulsifiable liquid
Carbamates
Aldicarb
Temik
Granular
Aldoxycarb
Standak
Flowable
OxamyI
Vydate
Granular or emulsifiable liquid
Carbofuran
Furadan/Curaterr
Granular or flowable
Cleothocarb
Lance
Granular
1 Use restricted.
Fumigants perform best in soils that do not have high levels of organic matter (which deactivates the toxicant) and that are free-draining but have adequate moisture. In general, fumigants are most effective in warm soils (12° to 15°C) as dispersion is temperature related.
Methyl bromide, the most dangerous of the fumigants still in common use, has to be applied beneath a polyethylene sheet. In some countries this is done with specialized machinery that treats and covers the soil in one operation. The cover is removed some days later and the crop is sown or planted when all traces of the fumigant have dispersed.
TABLE 2
Examples of recommended nematicidal dosages and treatments for some important crops1
Crop
Nematode pest
Nematicide
Application rate2
Application techniques
Potato
Globodera spp.
Aldicarb
2.24-3.36
Incorporated in row
Oxamyl
4.0-5.5
Carbofuran
4.0-5.5
Tomato, cucurbits
Meloidogyne spp.
Aldicarb
3.36
Incorporated in 30-cm bands
Ethoprophos
0.9-2.9
Incorporated in bands
OxamyI
0.6-1.2
Incorporated in bands
Fenamiphos
1.6-3.3
Incorporated in bands
Dazomet
30-50 g/m2
Incorporated in bands and irrigated Time interval before planting
Citrus
Tylenchulus semipenetrans
Fenamiphos
10.8-21.6
Annual treatment applied along drip-line
Aldicarb
5.5-11.0
Annual treatment applied along drip-line
Grape
Meloidogyne spp.
Fenamiphos
(e.c. formulation)
10.0
In bands for nursery use
Xiphinema index
Aldicarb
5-10
In bands for nursery use
Banana
Radopholus similis and/or
Carbofuran
2-4 ga.i. per plant
Applied around plant 2-3 times per year
Helicotylenchus multicinctus and/or
Ethoprophos
2-4 ga.i. per plant
Applied around plant 2-3 times per year
Pratylenchus spp. and/or
Fenamiphos
2-4 ga.i. per plant
Applied around plant 2-3 times per year
Meloidogyne spp.
Isazofos
2-4 ga.i. per plant
Applied around plant 2-3 times per year
Ebufos
2-4 ga.i. per plant
Applied around plant 2-3 times per year
1 Information taken from literature. Products may be unavailable for use in some countries. Economic and environmental justification should be evaluated before use. The omission of compounds does not imply that they are not equally suitable for nematode control.
2 kg a.i./ha unless otherwise stated.
Liquid fumigants EDB, metam-sodium and 1,3-D are applied to soil that has been prepared for planting. The soil surface is compacted with a roller after treatment which helps to seal the fumigant in the soil. Compounds releasing methyl isothiocyanate (dazomet, metam-sodium) work best in soils at >15°C. In cooler soils, the period between treatment and planting may have to be extended to allow sufficient time for the product to disperse.
The liquid fumigant DBCP is the only volatile compound that can be applied to growing plants without causing phytotoxicity. However, its manufacture has now ceased for toxicological reasons and its use is banned in many countries.
Non-volatile nematicides. A number of organophosphate and oximecarbamate nematicides were developed in the 1960s, which had the advantage that application was relatively simple (Wright, 1981). As a consequence nematicide use became more widely practised. These compounds (Table 1) are active at dosages of 2 to 10 kg a.i./ha which are smaller than the 200 to 300 litres/ha required for treatment with liquid fumigants. Most of the early formulations of these products were as granules that, when applied to the soil surface (or preferably incorporated in the top 10 cm of soil), release the active ingredient, which is spread through the soil by rainfall or irrigation. The efficacy of soil penetration depends on the amount of moisture, organic matter and soil structure. Heavy soils with relatively small pore spaces are more difficult to treat than sandy soils which have larger pore sizes. Some chemicals, particularly the organophosphates, are absorbed in organic matter, in which case efficacy may be impaired (Bromilow, 1980).
In general, distribution of the active ingredient or its toxic degradation products is less efficient than that of fumigants and results with granular nematicides have sometimes been inconsistent. To be effective, nematicides have to persist long enough for nematodes to be exposed to lethal concentrations, which may be as low as 1 to 2m g/litre. Extended persistence is, however, not desirable if there is a risk of residues in the crop or the active compounds contaminating groundwater.
Persistence of soil-applied nematicides depends on the soil characteristics. In warm countries, relatively high soil temperatures may accelerate the natural degradation of nematicides, and in protected crops where even higher soil temperatures than out-of-doors may occur, the effective life of a nematicide might be as short as one to three weeks (Bromilow, 1980). The repeated use of products of similar structure can lead to the selection of a soil microflora that metabolizes these compounds and decreases their persistence.
Side-effects
All nematicides are eventually degraded if they remain in the topsoil where there is greatest microbial activity. Once nematicides or their degradation products are flushed through the upper soil layers their persistence may be extended. It is the problem of toxic products in groundwater that has led to the prohibition of fumigant and non-fumigant nematicides in some countries. The permitted level of pesticide residues in drinking-water in the European Union is 0.1m g/litre. In regions of intensive agricultural production these tolerance levels may be exceeded at certain times of the year.
Nematicides are highly toxic compounds that have very low LD50 values. This is particularly important for operators of application machinery and people at risk from exposure to the chemicals during their application. The liquid formulations of some of the non-fumigant nematicides are emulsifiable concentrates. Their use should therefore be restricted to skilled operators who take adequate safety precautions. This may not always be the case where basic levels of education are poor or where operators cannot read the instructions on the labels of the products. The application of nematicides to crops too near to harvest is another risk which pesticide residue monitoring may not be sufficiently well coordinated to prevent.
The incidence of pesticide poisoning and mortality in some countries (Kottegoda, 1985) serves as a grim warning of the risks that arise when pesticides are widely used under poor management.
Chemical control of nematodes
The demand
The elimination of nematodes from some crops is essential for certain export requirements, particularly of high-value horticultural products. Chemical treatment with fumigants or nematicides may be the only technique available, and from the plant quarantine standpoint it is important that their use is retained.
The use of chemicals in protected cropping may still be preferable to other techniques such as steam treatment for economic and practical reasons. The use of soil-less growing media in some north European countries has resulted in a decreased demand for chemical treatments. In southern Europe, the Mediterranean region and North Africa, many horticultural and salad crops are grown in soil under polythene and soil treatment with methyl bromide, dazomet or non-fumigant nematicides is widely practised. The cost of such treatments may be as much as US$500 per hectare per year and can only be justified if the crops are of high market value.
Efficacy
Fumigants. Several general purpose fumigants give excellent control of nematodes in soil. The efficacy is related to their high volatility at ambient temperatures. All fumigants have low molecular weights and occur as gases or liquids. As they volatilize, the gas diffuses through the spaces between soil particles; nematodes living in these spaces are killed.
TABLE 1
Nematicides currently available on world markets
Chemical name
Trade name
Formulation
Fumigants
Methyl bromide
Dowfume
Gas
1,3 dichloropropene
Telone/DD-95
Liquid
Ethylene dibromide1
Dowfume W-85
Liquid
Metam-sodium
Vapam
Liquid
Dazomet
Basamid
Dust (prill)
Methyl isothiocyanate
Di-Trapex
Liquid
Chloropicrin1
Larvacide
Liquid
Organophosphates
Thionazin
Nemafos
Granular or emulsifiable liquid
Ethoprophos
Mocap
Granular or emulsifiable liquid
Fenamiphos
Nemacur
Granular or emulsifiable liquid
Fensulfothion
Dasanit
Granular
Terbufos
Counter
Granular
Isazofos
Miral
Granular or emulsifiable liquid
Ebufos
Rugby
Granular or emulsifiable liquid
Carbamates
Aldicarb
Temik
Granular
Aldoxycarb
Standak
Flowable
OxamyI
Vydate
Granular or emulsifiable liquid
Carbofuran
Furadan/Curaterr
Granular or flowable
Cleothocarb
Lance
Granular
1 Use restricted.
Fumigants perform best in soils that do not have high levels of organic matter (which deactivates the toxicant) and that are free-draining but have adequate moisture. In general, fumigants are most effective in warm soils (12° to 15°C) as dispersion is temperature related.
Methyl bromide, the most dangerous of the fumigants still in common use, has to be applied beneath a polyethylene sheet. In some countries this is done with specialized machinery that treats and covers the soil in one operation. The cover is removed some days later and the crop is sown or planted when all traces of the fumigant have dispersed.
TABLE 2
Examples of recommended nematicidal dosages and treatments for some important crops1
Crop
Nematode pest
Nematicide
Application rate2
Application techniques
Potato
Globodera spp.
Aldicarb
2.24-3.36
Incorporated in row
Oxamyl
4.0-5.5
Carbofuran
4.0-5.5
Tomato, cucurbits
Meloidogyne spp.
Aldicarb
3.36
Incorporated in 30-cm bands
Ethoprophos
0.9-2.9
Incorporated in bands
OxamyI
0.6-1.2
Incorporated in bands
Fenamiphos
1.6-3.3
Incorporated in bands
Dazomet
30-50 g/m2
Incorporated in bands and irrigated Time interval before planting
Citrus
Tylenchulus semipenetrans
Fenamiphos
10.8-21.6
Annual treatment applied along drip-line
Aldicarb
5.5-11.0
Annual treatment applied along drip-line
Grape
Meloidogyne spp.
Fenamiphos
(e.c. formulation)
10.0
In bands for nursery use
Xiphinema index
Aldicarb
5-10
In bands for nursery use
Banana
Radopholus similis and/or
Carbofuran
2-4 ga.i. per plant
Applied around plant 2-3 times per year
Helicotylenchus multicinctus and/or
Ethoprophos
2-4 ga.i. per plant
Applied around plant 2-3 times per year
Pratylenchus spp. and/or
Fenamiphos
2-4 ga.i. per plant
Applied around plant 2-3 times per year
Meloidogyne spp.
Isazofos
2-4 ga.i. per plant
Applied around plant 2-3 times per year
Ebufos
2-4 ga.i. per plant
Applied around plant 2-3 times per year
1 Information taken from literature. Products may be unavailable for use in some countries. Economic and environmental justification should be evaluated before use. The omission of compounds does not imply that they are not equally suitable for nematode control.
2 kg a.i./ha unless otherwise stated.
Liquid fumigants EDB, metam-sodium and 1,3-D are applied to soil that has been prepared for planting. The soil surface is compacted with a roller after treatment which helps to seal the fumigant in the soil. Compounds releasing methyl isothiocyanate (dazomet, metam-sodium) work best in soils at >15°C. In cooler soils, the period between treatment and planting may have to be extended to allow sufficient time for the product to disperse.
The liquid fumigant DBCP is the only volatile compound that can be applied to growing plants without causing phytotoxicity. However, its manufacture has now ceased for toxicological reasons and its use is banned in many countries.
Non-volatile nematicides. A number of organophosphate and oximecarbamate nematicides were developed in the 1960s, which had the advantage that application was relatively simple (Wright, 1981). As a consequence nematicide use became more widely practised. These compounds (Table 1) are active at dosages of 2 to 10 kg a.i./ha which are smaller than the 200 to 300 litres/ha required for treatment with liquid fumigants. Most of the early formulations of these products were as granules that, when applied to the soil surface (or preferably incorporated in the top 10 cm of soil), release the active ingredient, which is spread through the soil by rainfall or irrigation. The efficacy of soil penetration depends on the amount of moisture, organic matter and soil structure. Heavy soils with relatively small pore spaces are more difficult to treat than sandy soils which have larger pore sizes. Some chemicals, particularly the organophosphates, are absorbed in organic matter, in which case efficacy may be impaired (Bromilow, 1980).
In general, distribution of the active ingredient or its toxic degradation products is less efficient than that of fumigants and results with granular nematicides have sometimes been inconsistent. To be effective, nematicides have to persist long enough for nematodes to be exposed to lethal concentrations, which may be as low as 1 to 2m g/litre. Extended persistence is, however, not desirable if there is a risk of residues in the crop or the active compounds contaminating groundwater.
Persistence of soil-applied nematicides depends on the soil characteristics. In warm countries, relatively high soil temperatures may accelerate the natural degradation of nematicides, and in protected crops where even higher soil temperatures than out-of-doors may occur, the effective life of a nematicide might be as short as one to three weeks (Bromilow, 1980). The repeated use of products of similar structure can lead to the selection of a soil microflora that metabolizes these compounds and decreases their persistence.
Side-effects
All nematicides are eventually degraded if they remain in the topsoil where there is greatest microbial activity. Once nematicides or their degradation products are flushed through the upper soil layers their persistence may be extended. It is the problem of toxic products in groundwater that has led to the prohibition of fumigant and non-fumigant nematicides in some countries. The permitted level of pesticide residues in drinking-water in the European Union is 0.1m g/litre. In regions of intensive agricultural production these tolerance levels may be exceeded at certain times of the year.
Nematicides are highly toxic compounds that have very low LD50 values. This is particularly important for operators of application machinery and people at risk from exposure to the chemicals during their application. The liquid formulations of some of the non-fumigant nematicides are emulsifiable concentrates. Their use should therefore be restricted to skilled operators who take adequate safety precautions. This may not always be the case where basic levels of education are poor or where operators cannot read the instructions on the labels of the products. The application of nematicides to crops too near to harvest is another risk which pesticide residue monitoring may not be sufficiently well coordinated to prevent.
The incidence of pesticide poisoning and mortality in some countries (Kottegoda, 1985) serves as a grim warning of the risks that arise when pesticides are widely used under poor management.
I gave you the heads up though.
.
