IRAC-Nematicide – Mode of Action (MOA) Classification Poster

Nematicides are class of chemicals or biologicals, which kill nematodes (microscopic, worm-like organisms that feed on plant roots). It’s used to protect plants or plant products against all harmful organisms nematodes.

Although no substantiated examples of nematicide resistance resulting in failure of commercial nematicides in agriculture have been documented in the past 100 years, under intense laboratory selection reduced susceptibility to nematicides has been demonstrated.

Thus, as a proactive informational measure, the nematicide MoA Classification has been developed to provide manufactures, regulatory agencies, and other organizations with an MoA reference point for nematicides.

IRAC Mode of Action classification for Nematodes listing the Nematicide Groups Numbers, Mode of action type, and Chemical Groups.

IRAC Mode of Action Classification Scheme published in March 2020, doesn’t cover selective nematicides in the classification.

IRAC has recently added an entirely new MoA classification specifically addressing nematicides.

In 2019 IRAC published a nematicide MoA Classification poster, which incorporates a wide range of active ingredients including conventional nematicides, fumigants, and biologics known as classical Nematicides. Colour code for nematicide poster; blue – nerve and muscle (i.e. carbamates, OPs, and avermectins), magenta – pyridinylmethyl benzamides, green – tetronic and tetramic acid derivatives, gray – Unknown, aqua – biologicals.

Conventional nematicides are as follows:

1. 1. 1. Carbamate (Group N-1A),
      2. Organophosphate (Group N1B) compounds,
      3. Avermectins (abamectin, Group N-2),
      4. Pyridinylmethyl benzamides (fluopyram, Group N-3),
      5. Tetramic acids (spirotetramat, Group N-4)
      6. The group of compounds (Group N-UN) with unknown MoAs, and
      7. The group of fumigants (Group N-UNX).

Table 1: IRAC Mode of action classification for nematicides.

Nema Group	Chemical subgroup / exemplifying active	Primary site of action / MoA	Representative a	IRAC/FRAC Group b
			AI / biologic
N-1	N-1A Carbamates	AChE inhibitors	Oxamyl	IRAC 1A
	N-1B Organophosphates	AChE inhibitors	Fosthiazate	IRAC 1B
N-2	Avermectins	Glu-Cl allosteric modulators	Abamectin	IRAC 6
N-3	Pyridinylmethyl-benzamides	MET II inhibitors	Fluopyram	FRAC 22
N-4	Tetramic acids	Inhibitors of ACCase	Spirotetramat	IRAC 23
N-UN	imidazopyridine	Unknown	Fluazaindolizine	–
	Heterocyclic fluoroalkenyl sulfone	Unknown	Fluensulfone	–
	Cyclic aldehyde	Unknown	Furfural	–
	Dicarboximide	Unknown	Ipodione	–
	Disubstituted oxadiazole	Unknown	Tioxazafen	–
N-UNX	Volatile sulfur generator	Unknown, multi-site	Carbon disulfide	–
	Carbon disulfide liberator	Unknown, multi-site	Sodium tetrathiocarbonate	–
	Alkyl halides	Unknown, multi-site	Methyl bromide	IRAC 8A
	Halogenated hydrocarbon	Unknown, multi-site	1,3-dichlorpropene	IRAC 8A
	chloropicrin	Unknown, multi-site	Chloropicrin	IRAC 8B
	Methyl isothiocyanate generator	Unknown, multi-site	Diazomet	IRAC 8F
N-UNB	Biological – bacterium	Unknown, bacterial action	Bacillus firmus I-1582
N-UNF	Biological – fungus	Unknown, fungus	Purpureocillium lilacinum
N-UNE	Biological	Unknown, botanical / plant origin	Pongamia oil	–
	Biological – tetranortriterpines	Unknown, botanical / plant origin	Azadiractin	IRAC UN
	Biological – saponins from Quillaja saponaria tree	Unknown, botanical / plant origin	Quillaja saponaria extract	–
	Biological – essential oil	Unknown, botanical / plant origin	Carvacrol	IRAC UNE

^a Representative compound / active within an IRAC grouping.

^b Equivalent IRAC or FRAC grouping.

Nematicides (Unidentified MoAs): 

Among these recent nematicides with as yet unidentified MoAs are tioxazafen (South et al., 2019), fluazaindolizine (Lahm et al., 2019), and fluensulfone (Maienfisch et al., 2019).

The recent development of biologics for plant-parasitic nematode control (Maienfisch et al., 2019) provides added options for growers.

The biologics for nematode control have been divided into three Groups; bacteria (N-UNB), fungi (N-UNF), and botanical / animal derivatives, and extracts (N-UNE).

The present update reflects the new addition of a Nematicide MoA Classification also recognizes the growing interest and focus on new compounds for nematode control, and as tools for integrated nematode management.

About IRAC Nematode Group:

The IRAC Nematode Working Group is the most recently established IRAC team. The initial objectives of the team will be to investigate the resistance risk of nematicides and to develop a mode of action classification scheme similar to that available for insecticides and acaricides.

There is clear evidence that nematicide resistance can occur under laboratory conditions, but it is less clear if field resistance can occur under natural conditions. There is however some evidence to show that increased degradation of nematicides and other pesticides can occur through increased microbial activity in the soil (not classical resistance, but with similar impact). Enhanced pesticide metabolism in soil, tends to be chemical class-specific, which means nematicide/insecticide rotation or reduction in application intervals can slow its occurrence.

Resistance risk can vary significantly between crops, with row crops being considered low risk (low number of applications), whilst others receive multiple applications per year/season (e.g. banana, vegetables).

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