Fungicidal control of plant disease: modes of action and fungal resistance

Delp C.J., . (1990) Fungicidal control of plant disease: modes of action and fungal resistance. [Proceedings Paper]

Plant diseases cause serious losses if not managed with biological chemical and/or cultural methods. Currently available biological including host resistance and cultural methods are insufficient in many cases and some critical plant diseases must be controlled by fungicides. The older less effective fungicides have to be applied in relatively high doses kgs/ha and frequencies to protect before infection occurs. These chemicals kill fungi by inhibiting several vital activities of the fungus. This is called multisite action. In the last 20 years many highly active fungicides have been developed for the control of many serious diseases. A significant characteristic is their specific site of action - the inhibition of a specific and vital function in the fungus. Some examples are described with emphasis on three groups of fungicides that have been broadly used and abused. 1. The benzimidazoles bind to a protein subunit of the spindle. That stops cell division in sensitive fungi. 2. The DMI fungicides interfere with the synthesis of sterols necessary for fungal growth. 3. Phenylamides inhibit RNA synthesis in many of the Oomycete fungi such as downy mildews Pythium and Phytophthora species. Unfortunately there are strains of pathogenic fungi with genetic characteristics that make them resistant to some fungicides. Normally these resistant strains are in a very low proportion of the wild sensitive population. But with the exclusive intensive use of a site-specific fungicide the resistant strains may become a dominant part of the population and result in the loss of fungicide effectiveness. Resistant strains may be easy to develop in the laboratory and may be isolated from the field. But the influence of these resistant strains must be correlated with significant levels in a population and the loss of effectiveness of a fungicide under recommended use conditions before the phenomenon should be called practical resistance. Resistance management strategies include such tactics as the use of integrated disease management reduced applications and the use of mixtures and alternations with fungicides that are not cross resistant

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Abstract

Plant diseases cause serious losses if not managed with biological chemical and/or cultural methods. Currently available biological including host resistance and cultural methods are insufficient in many cases and some critical plant diseases must be controlled by fungicides. The older less effective fungicides have to be applied in relatively high doses kgs/ha and frequencies to protect before infection occurs. These chemicals kill fungi by inhibiting several vital activities of the fungus. This is called multisite action. In the last 20 years many highly active fungicides have been developed for the control of many serious diseases. A significant characteristic is their specific site of action - the inhibition of a specific and vital function in the fungus. Some examples are described with emphasis on three groups of fungicides that have been broadly used and abused. 1. The benzimidazoles bind to a protein subunit of the spindle. That stops cell division in sensitive fungi. 2. The DMI fungicides interfere with the synthesis of sterols necessary for fungal growth. 3. Phenylamides inhibit RNA synthesis in many of the Oomycete fungi such as downy mildews Pythium and Phytophthora species. Unfortunately there are strains of pathogenic fungi with genetic characteristics that make them resistant to some fungicides. Normally these resistant strains are in a very low proportion of the wild sensitive population. But with the exclusive intensive use of a site-specific fungicide the resistant strains may become a dominant part of the population and result in the loss of fungicide effectiveness. Resistant strains may be easy to develop in the laboratory and may be isolated from the field. But the influence of these resistant strains must be correlated with significant levels in a population and the loss of effectiveness of a fungicide under recommended use conditions before the phenomenon should be called practical resistance. Resistance management strategies include such tactics as the use of integrated disease management reduced applications and the use of mixtures and alternations with fungicides that are not cross resistant

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Item Type:	Proceedings Paper
Additional Information:	13 ref.; Summary En
AGROVOC Term:	FUNGICIDAS
AGROVOC Term:	ENFERMEDADES DE LAS PLANTAS
Geographical Term:	MALAYSIA
Depositing User:	Ms. Norfaezah Khomsan
Last Modified:	24 Apr 2025 05:26
URI:	http://webagris.upm.edu.my/id/eprint/15021

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