Benzimidazole management strategy
Resistance to benzimidazole fungicides is common
in many Botrytis cinerea populations affecting
outdoor and greenhouse crops.
(Photo: Dion Mundy)."
(Revised February 2004)
A new fungicide resistance management strategy for apple black spot (Venturia inaequalis) has been put in place and supersedes the individual Mode of Action strategies shown elsewhere on this site for apple black spot in pipfruit.
The new strategy is available here.
This fungicide use strategy is designed to manage the problem of resistance to benzimidazole (also known as MBC) fungicides in New Zealand. It has been developed from previously published information (Tate et al. 1996) in consultation with the New Zealand agricultural chemical industry (Agcarm Inc.). It incorporates recommendations from the Fungicide Resistance Action Committee (FRAC) in Europe.
Benzimidazole product perspective
Benzimidazole fungicides include benomyl, carbendazim, fuberidazole, thiabendazole, thiophanate and thiophanate-methyl. They all generate MBC (methyl benzimidazol carbamate), either as the principal active ingredient, or as a breakdown compound formed on mixing with water. They have a common mode of action, interfering with cell division and hyphal growth of sensitive fungi. They are upwardly systemic with a broad range of activity against ascomycetes, fungi imperfecti and basidiomycetes (Table 1).
Benzimidazole fungicides were first introduced into New Zealand in the late 1960s and they offered systemic, curative fungicidal activity on a number of problem diseases. Those currently available are shown in Table 2.
|Beans, berryfruit, grapes
|Beans, lettuce, tobacco, tomatoes, kiwifruit
|Speckled leaf blotch
|Venturia inaequalis1, Venturia pirina
|Stem end rot
|Celery leaf spot
|Carnation stub dieback
|Garlic clove rot
1Diseases for which resistant strains have been identified in New Zealand.
in Chlorocarb with chlorothalonil
MBC 800 WDG
|in Baytan Universal with triadimenol and imazalil
|in Combo with chlorothalonil
in Greenguard with chlorothalonil
in Guardall Liquid with chlorothalonil
in Taratek with chlorothalonil
Topsin M-4 A
|in Aliette Super with fosetyl aluminium and thiram
Current status of benzimidazole resistance in New Zealand
Resistance to benzimidazole fungicides is widespread among target pathogens (Table 1). Lack of disease control and yield loss are common when resistance occurs. Strains resistant to one benzimidazole fungicide are cross-resistant to other fungicides in this group. Resistance occurs as a result of a single gene mutation. Resistant strains are genetically stable and usually of equal fitness to sensitive strains and they persist even after benzimidazole use is discontinued. Resistance frequencies vary considerably, depending on the cropping history and amount of benzimidazole use. Control failure and publicity about the potential for resistance to develop has reduced the use of benzimidazole fungicides, but they are still effectively used in some situations. Benzimidazole resistance has not been found in New Zealand or elsewhere to some important pathogens, such as Pithomyces chartarum, Sclerotinia sclerotiorum, S. minor and Podosphaeria leucotricha.
Alternative fungicides are available and these have sometimes become predominant where benzimidazoles were used intensively in the past. Where resistance has developed or threatens to develop against some of the alternative products, particularly dicarboximides, benzimidazoles can be reconsidered for tactical use, particularly where benzimidazole resistant strains are not common. Dual resistance in Botrytis cinerea to both benzimidazoles and dicarboximides has been observed where benomyl has been used on kiwifruit against S. sclerotiorum. The use of benzimidazoles during bloom against S. sclerotiorum has reduced effectiveness of dicarboximides against B. cinerea preharvest. Dual resistance also occurs for benzimidazoles and dicarboximides in M. fructicola in stonefruit.
Resistance management strategy
Avoid benzimidazole use where resistant strains of the pathogen are known or are likely to occur. If resistance frequency is nil or low, use a maximum of two applications per crop per 12 month period (see Table 3 for exceptions), including crops where benzimidazoles may be indicated for the control of two or more pathogens, e.g. Sclerotinia spp. and Botrytis spp. in vegetables. Confine use to periods when disease risk is high, but disease level is low. Where practical apply in a mixture with a protectant fungicide. Comply with the label application rates at all times. Practise good crop hygiene and cultural controls. Using dicarboximides and benzimidazoles in the same spray programme may lead to development of pathogen strains with dual resistance and should be avoided.
|Confine use to the blossom period only.
Botrytis dry eye rot
|Confine use to the blossom period and use a fungicide from another group for black spot control.
Apply only in mixture with a protectant fungicide e.g. thiram, captan, mancozeb or metiram.
tomatoes, and beans
|Grey mould (botrytis)
|Avoid use if resistance is known to be present, otherwise do not exceed one application per season.
|Use in mixture or alternation with alternative products.
|Tomatoes, beans and lettuce
|Limit use to early season (blossom to 14 days post-blossom on flowering crops).
|Apply only in second year crop. If control was below expectation use an alternative in the third year.
|Speckled leaf blotch
|Comply strictly with recommended timing (last week of August).
|Comply with label rates and timing.
Product labels should include a statement about resistance risk and a recommendation about the maximum numbers of benzimidazole fungicides that should be applied.
This resistance management strategy has been compiled with assistance from Jack Richardson (Agcarm Inc.) and Matthew Cromey (Crop & Food Research).
Tate G, Fullerton R, Cornwall M 1996. Benzimidazole resistance management strategy. In: Boudot GW, Suckling DM ed. Pesticide resistance prevention and management. New Zealand Plant Protection Society, Rotorua, New Zealand. Pp. 146-150.