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Mancozeb UPDATE

History

Mancozeb was first registered in 1962 as a fungicide and after over 50 years it still has an important role to play. Globally mancozeb is registered for use on over 70 different crops and offers protection against more than 400 diseases. United Phosphorus Ltd (UPL) acquired the global non-mixture mancozeb fungicide business and related assets from DuPont in 2010/11. This made UPL the 2nd largest global manufacturer of mancozeb. Products containing mancozeb that are currently marketed in the UK by UPL are shown in Table 1.

Table 1 Mancozeb containing products marketed in the UK by UPL

Maximum number Maximum Maximum Harvest Active MAPP of applications individual dose total dose interval Product name ingredient number per crop (kg/ha/yr) (kg/ha/yr) (days) LERAP

Manzate 75WG 750 mancozeb 15052 8 1.7 – 7 B

Nautile DG 680 mancozeb 14692 Not stated 1.8 No limit 7 50 cymoxanil

Penncozeb 80WP 800 mancozeb 14718 8 1.7 – 7 B

Video DG 680 mancozeb 14850 Not stated 1.8 No limit 7 50 cymoxanil

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Mode of action and properties of mancozeb

Mancozeb belongs to the dithocarbamate grouping of fungicides and to the class of compounds known as ethylene bisdithiocarbamates (EHBDCs). The Fungicide Resistance Action Committee (FRAC) places the dithiocarbamates into the mode of action group M (Multi-site Action), see Table 2. During its long history there have been no cases of resistance recorded against mancozeb.

Table 2. Mancozeb properties

FRAC code Mode of action and mobility Resistance risk Use in potatoes

M3 Multi-site inhibitor No resistance detected Can be used throughout the season, at 7-14 day intervals

Protectant, non-systemic Has been used globally A good partner for at risk since the 1960s active substances

Can be used alone

The diagram in Figure 1 shows visually the target sites of common fungicides approved for use on potatoes in the UK and Table 4 provides a summary of the modes of action of fungicide actives. Due to the multi-site mode of action of mancozeb it exhibits a low risk of resistance developing. Mancozeb itself is not fungicidal, only when it is exposed to water does it break down to release ethylene bisiothiocyanate sulphide (EBIS) which in turn via the action of UV light is then converted into ethylene bisisothiocyante (EBI). EBIS and EBI are thought to interfere with biochemical processes within the fungal cell cytoplasm and mitochondria which results in inhibition of spore germination. The activity of mancozeb is purely protective in that the compound remains on the leaf surface and does not penetrate through the cuticle, no systemic redistribution occurs, it does not have any curative fungicidal properties.

Control of late blight, Phytophthora infestans

Late blight, caused by Phytophthora infestans, is the most important disease in potato production in the UK. In extreme situations it can cause 100% crop loss.

Continuing research work in Europe (and funded by the Potato Council in Great Britain) has demonstrated a continuously changing pattern of strains of blight. Some of these strains can sometimes show differing levels of

sensitivity to certain fungicides, but not mancozeb, whose blight protection remains sound. This is another good reason why mancozeb should be part of the core of every blight fungicide programme.

Control of early blight, Alternaria solani and Alternaria alternata

Many newer fungicide products used on the potato crop in the UK for late blight control are not effective against ‘early blight’. This is caused by two fungal species; Alternaria solani and Alternaria alternata. Growers need to be aware of these potentially damaging pathogens and also realise that some potato varieties are more susceptible than others. Some industry experts believe that the increase in Alternaria is at least in part due to a reduction in the use of mancozeb within potato blight programmes, because mancozeb is known to provide effective protection against this disease. Advice is to include at least 1500g/ha of mancozeb per application within the early stages of a potato fungicide programme, either as part of a formulated product or as an ‘add in’ straight. This is particularly important on varieties that are known to be more susceptible to Alternaria. See Table 3. Where control of Alternaria is required, mancozeb must be applied before the disease ‘takes hold’ as it acts only as a protectant.

Table 3. Potato variety susceptibility to Alternaria

Very susceptible Markies

Moderately susceptible Ramos, Saturna, Lady Claire, Russet Burbank, Wilja

Table 4. Mode of action of key potato fungicide actives

Active FRAC code Mode of action Target code Target site Group name

dimethomorph 40 Cell wall H5 Cellulose carboxylic acid benthiavalicarbisopropyl biosynthesis synthase amides mandipropamid

propamocarb 28 Lipid synthesis F4 Cell membrane carbamates and membrane permeability, integrity fatty acids

zoxamide 22 Mitosis and B3 ß-tubulin assembly benzamides cell division in mitosis and thiazole- carboxamides

fluopicolide 43 Mitosis and B5 Delocalisation of benzamides cell division spectrin like proteins

mancozeb M3 Multi-site contact M3 Multi-site contact activity dithiocarbamates maneb

chlorothalonil M5 Multi-site contact M5 Multi-site contact activity chloronitriles

benalaxyl 4 Nucleic acids A1 RNA polymerase I phenylamides metalaxyl-M synthesis

boscalid 7 Respiration C2 Inhibition of Complex II: SDHI succinate-dehydrogenase

azoxystrobin 11 Respiration C3 Inhibition of Complex III: QoI-fungicides pyraclostrobin cytochrome bc1 famoxadone at Qo site fenamidone

amisulbrom 21 Respiration C4 Inhibition of Complex III: QiI-fungicides cyazofamid cytochrome bc1 at Qi site

fluazinam 29 Respiration C5 Uncoupler of oxidative Uncoupler of phosphorylation oxidative phosphorylation

ametoctradin 45 Respiration C8 Complex III: cytochrome QxI-fungicide bc1 at Q at unknown site

cymoxanil 27 Unknown U27 Unknown cyanoacetamide- oximes

Figure 1. Target sites of potato fungicides

Lipid synthesis and membrane integrity

Mitosis and cell division

Nucleic acids synthesis

Respiration

Cell wall biosynthesis

Nucleus

Vacuole

Mitochondria

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Regulatory issues – key points

• UPL is committed to the regulatory support of EBDC containing products including mancozeb

• The new proposed Annex 1 expiry date for mancozeb is January 2018

• The criteria for categorising ‘Endocrine Disruptors’ has not yet been finalised

• Recently mancozeb received a default endocrine categorisation which has to be disproved during its renewal in order for it to remain on the market

• UPL is undertaking extensive work to demonstrate and defend the safety of mancozeb and expect to be able to demonstrate the safety of this active and maintain registrations in years to come.

Summary

Mancozeb is a critical component of resistance management and integrated disease management programs for early and late potato blight control in the UK.

References

Gullino M.L et al (2010). Mancozeb, Past, Present and Future Plant Disease, vol 94, p.1076-1087.

Fungicide Resistance Action Group UK (FRAG-UK) Potato late blight: Guidelines for managing fungicides resistance.

Managing the risk of late blight: British Potato Council.

Contacts

Chris Delf Sales Manager UK & Ireland M: 07793 936 652 E: chris.delf@uniphos.com

Richard Allen Sales Manager UK M: 07831 346 369 E: rallen@uniphos.com

David Raine Sales Scotland M: 07584 172 229

Pam Chambers Technical Support Manager UK & Ireland M: 07809 227 583 E: pam.chambers@uniphos.com

Louise Dalgliesh Campaign Manager UK & Ireland M: 07584 172 970 E: ldalgliesh@uniphos.com

Information in this booklet does not constitute a recommendation, it is for guidance only. Up to date information can be found on our web site www.upleurope.com.

Brand names used in this guide may be trademarks of other manufacturers, in which proprietary rights may exist.

Use plant protection products safely.

Always read the label and product information before use.