A MANDA C OTTAGE 1 AND P ETER U RWIN 2 **
16.1. History and Development of Nematicides
16.2.1. Fumigant nematicides 463
16.2.2. Non-fumigant nematicides 464
16.3. Formulation and Application 464
16.3.1. Liquid formulations 464
16.3.2. Microgranules 465
16.3.3. Fumigants 469
16.4. Nematicides in the Environment 471
16.4.1. Degradation 471
16.4.2. Non-target organisms and groundwater 472
16.4.3. Ozone depletion and methyl bromide 473
16.4.4. Legislation 474
16.5. Human Safety 475
16.5.1. Exposure during application 475
16.5.2. Residues in foodstuffs 476
16.5.3. Product stewardship 477
16.6. Naturally Occurring Nematicides 477
16.1. History and Development of Nematicides
The UK’s Chemicals Regulation Directorate defines a pesticide as ‘any substance, preparation or organism prepared or used for controlling any pest. A pesticide prod- uct consists of one or more active substance (a.s.) co-formulated with other materials’
and a nematicide is classed as ‘a pesticide used to control unwanted nematodes’
(http://www.pesticides.gov.uk/guidance/industries/pesticides). However, whilst some biological control agents for nematodes are classified for registration purposes as
16 Chemical Control of Nematodes*
PATRICK P.J. HAYDOCK,† SIMON R. WOODS, IVAN G. GROVE** AND MARTIN C. HARE
Crop and Environment Research Centre, Harper Adams University, UK
* A revision of Haydock, P.P.J. et al. (2006) Chemical control of nematodes. In: Perry, R.N.
and Moens, M. (eds) Plant Nematology, 1st edn. CAB International, Wallingford, UK.
** Corresponding author: igrove@harper-adams.ac.uk
† Pat Haydock died on 11 August 2012.
nematicides within the UK and EU, they will not be discussed here as they are con- sidered separately in Chapter 13. Nematicides are chemical compounds that are lethal to nematodes, whereas the terms ‘nematistat’ or ‘nematistatic’ (see Chapter 10) are frequently used for compounds that provide sub-lethal dosages, which disrupt nema- tode behaviour. These latter chemicals work by paralysing the nematodes for a vari- able period of time, during which they may deplete their lipid reserves to such an extent that they are unable to invade the plant. Nematode recovery is possible from the sub-lethal effects of nematistats. The term nematicide is commonly used as an umbrella term encompassing both types of activity and will be used in this sense here.
Nematicides are applied primarily to reduce root/plant damage caused by nematodes and to increase productivity (Tobin et al., 2008), which is achieved by reducing the num- bers of nematodes feeding on (e.g. Trichodorus spp.) or in (e.g. Meloidogyne spp., Globodera spp.) plant tissues. Nematicides are also applied to prevent or reduce nema- tode reproduction and to limit the transmission of nematode-borne viruses to the plant (Daleet al., 2004). The economic benefit to the crop is seen as a reduction in yield loss (and/or an increase in quality), maintenance of future production and profitability.
Nematicide application has been shown significantly to reduce a wide number of plant- feeding nematodes (Eisenhauer et al., 2010); however, reductions in nematode population densities do not always occur, particularly where the nematode’s reproductive rate is high or multiple generations of the nematode occur during the growth period of the crop. For example with the potato cyst nematode, Globodera pallida, in the UK the damage threshold for an intolerant cultivar is approximately 1–3 eggs g−1 soil. The greater the initial popula- tion density the greater the level of control required to achieve this low level. Population multiplication on a susceptible cultivar is inversely density dependent (Chapter 11), but in practice is rarely more than 50-fold, so that a reduction in initial population density of 98% should result in full control (Whitehead and Turner, 1998). This degree of control is rarely achieved and the use of nematicides will need to be combined with other meas- ures such as crop rotation and plant resistance as part of an integrated management strategy. Modelling of G. pallida populations has shown that egg survival following nematicide treatment is often sufficient to allow large populations to ‘rebound’. This has been supported by field experiments showing that G. pallida population increase was almost as great in nematicide treated as in untreated plots (Trudgill et al., 2003).
Nematicides have been in use since the late 19th century when the fumigant carbon disulphide was introduced. Development of further fumigants took place in the first half of the 20th century with the introduction of chloropicrin, 1,3-dichloropropene (1,3-D), methyl bromide, 1,2-dibromo-3-chloropropane (1,2-DBCP), 1,3-dichloropropene and 1,2-dichloropropane mixtures (DD), formaldehyde, metam sodium and dazomet.
The remaining uses of methyl bromide were revoked for developed countries in 2005 under the Montreal Protocol for the reduction of gases contributing to global warming, although critical use exemptions still apply (Section 16.4.3). Similarly, 1,3-dichloropropene (1,3-D) is now banned in the EU but continues to be used in the USA (http://iaspub.
epa.gov/apex/pesticides/f?p=PPLS:102:::NO::P102_REG_NUM:62719-32) and is being registered for use in China (Qiao et al., 2012). The second half of the 20th century saw the development of the organophosphates such as fenamiphos, ethoprophos and fosthiazate, together with the carbamates carbofuran, aldicarb and oxamyl (Table 16.1). The most recent addition to the nematicide options is fluensulfone, a fluoroalkenyl systemic non-fumigant (Oka et al., 2012). The process of nematicide discovery and testing is outlined in Box 16.1. The late 20th and early 21st century
Chemical Control of Nematodes461
Table 16.1. Globally important nematicides.
Active substance Chemical group
LD50 (acute oral male rats)
Year of discovery
Example trade name
State of
formulation Manufacturer
Abamectin Avermectins 10 mg kg−1 1979 Avicta 500FS Liquid Syngenta
http://www.Syngenta.com
Aldicarb1 Oxime carbamate 0.93 1965 Temik 15G Microgranule
Microgranule
Bayer CropScience
http://www.bayercropscience.com
Carbofuran Carbamate 8 1965 Furadan 15G
Furadan 4F
Microgranule Liquid
FMC Corporation http://www.fmc.com
Cadusafos1 Organophosphorus 37 1982 Rugby 200 CS
Rugby 10G
Liquid Microgranule
FMC Corporation http://www.fmc.com
Dazomet Methyl
isothiocyanate2 liberator
77–2202 1897 Basamid Microgranule BASF Corporation
http://www.agriculturalproducts.
basf.com 1,3-dichloropropene Halogenated
hydrocarbon
150 1956 Telone ll
Telone EC
Liquid Liquid
Dow AgroSciences http://www.dowagro.com
Ethoprophos Organophosphorus 62 1966 Mocap 10G
Mocap EC
Microgranule Liquid
Bayer CropScience
http://www.bayercropscience.com
Fenamiphos Organophosphorus 6 1967 Nemacur 15G
Nemacur 3
Microgranule Liquid
Bayer CropScience
http://www.bayercropscience.com
Fosthiazate Organophosphorus 73 1992 Nemathorin
10G
Microgranule Syngenta
http://www.syngenta.com
Iprodione Dicarboximides >2000 1974 (a.s.) Enclosure® Liquid Devgen nv
http://www.devgen.com Metam sodium (sodium
N-methyldithiocarbamate)
Methyl isothiocyanate liberator
77–2202 1951 Vapam
Vapam HL
Liquid Liquid
Amvac Chemical Corporation http://www.amvac-chemical.com
Oxamyl Oxime carbamate 3.1 1974 Vydate 10G
Vydate L
Microgranule Liquid
Du Pont
http://www.1.dupont.com
1Chemicals such as aldicarb and cadusafos have now been banned, restricted or are under licence revocation in several countries.
2LD50 is for methyl isothicyanate.
Box 16.1. Nematicide discovery and evaluation.
Sources of potential nematicides for a crop protection company
‘In-house’, produced by chemical synthesis
in the laboratory by
‘discovery’ team.
External sources, e.g. universities and other companies.
Natural sources, e.g. bacteria, fungi, plants.
Primary biological or biochemical screen
• Automated biochemical micro-titre screening allows several hundred thousand chemicals to be screened each year by an individual company.
• Several thousand compounds can be tested using the whole organism, e.g.Meloidogynespp.
• Chemicals are initially tested at high dose rates.
Product development and marketing
• It usually takes 8–10 years and costs approximately US$60 million(€47 million) to take a chemical from primary screening through to the launch of a new nematicide.
Efficacy, toxicity, ecotoxicity, residue and formulation testing
• Continuation of glasshouse studies.
• Use of field microplots and full field experiments to evaluate the chemical’s effect on plant growth, yield, quality and nematode reproductive rates.
• Evaluation of environmental impact in field conditions.
• Generation of efficacy data for registration purposes requires field testing over several sites and years.
• See guidelines for the European Union (Anon., 2004) and the USA (http://www.epa.gov).
Activity screen
• Candidate chemicals are compared in planta with a standard nematicide at different dose rates against a range of important nematode species.
• Studies on the chemical’s physicochemical properties, toxicity and environmental profile commence.
has seen more research and development to improve the efficiency of use of nemati- cides, to minimize their environmental impact and to reduce their cost to growers.
There has also been increased interest in and development of ‘natural’ nematicides, derived mainly from plant extracts and bacteria (Section 16.6). Avermectins (B1a and B1b) derived from the soil bacterium Streptomyces avermitilis are the components of the nematicide abamectin.
Nematicides continue to be an important part of nematode management pro- grammes, whether used as part of an integrated management approach or as the sole control component (Hillocks, 2012; Qiao et al., 2012). The global market for nemati- cides is suggested to be worth US$1 billion (approximately €755 million) per annum, utilizing in the order of 350,000 t of active substance each year, with the annual cost from loss of production due to nematodes at US$80–125 billion. Approximate usage by crop and nematode group is given in Table 16.2. Vegetable crops account for the greatest proportion of nematicide use where Meloidogyne spp. are the target for approximately half of the world’s usage and so are of major concern when developing new products.