Revista Brasileira De Herbicidas 2016; 15(1): 107-115
Herbicide action in the severity of diseases in cultivated plants
The severity of diseases in plants can be affected by practices such as the application of herbicides for the control of weeds. Therefore, we aimed to present and discuss the relationship between the use of herbicides and the severity of diseases of cultivated plants. After contact, the pathogens try to infect and colonize the hosts, which, in turn, use mechanisms to defend themselves from infection. The trichomes, the cuticles and the epicuticular wax are barriers against penetration. Phenolic compounds, enzymes and phytoalexins are substances synthesized by plants and toxic to the pathogens. The herbicide action influences the severity of diseases indirectly on the defense mechanisms of plants or directly when it presents toxic effects to the pathogens. The effect of adjuvants in the commercial formula of herbicides causes degradation of trichomes, epicuticular waxes and cuticles, favoring penetration of pathogens. Harmful effects on the physiology and secondary metabolism of plants, caused by herbicides, affects the synthesis of the above mentioned defense compounds. However, the herbicide molecules may inhibit the germination of spores and the growth of fungal hyphae, which results on the reduction of the infection and colonization. Necrotic points resulting from herbicide action may make plants less prone to the occurrence of rust, mildews and powdery mildews, caused by biotrophic fungi. Herbicides also have secondary effects such as population reduction of alternative host plants and vector insects. The relationship between herbicides and the severity of diseases in crops is an important tool for the phytosanitary management in an integrated way.
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