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Qo inhibitors (QoI), or quinone outside inhibitors, are a group of fungicides used in agriculture. They represent the most important development made in fungicides by the chemicals industry. QoI are chemical compounds which act at the quinol outer binding site of the cytochrome bc1 complex.
QoI's are the resulting fusion of three fungicides families, the well-known family of strobilurins and two new families, represented by fenamidone and famoxadone. Some strobilurins are azoxystrobin, kresoxim-methyl, picoxystrobin, pyraclostrobin, and trifloxystrobin.
These fungicides are used on a wide range of crops, such as cereals, vines, pome fruits, cucurbits, tomatoes and potatoes.
For example, they are used as fungicides for cereals, against Erysiphe graminis f.sp tritici responsible for the powdery mildew in wheat or against Septoria tritici, responsible for septoria leaf spot in wheat.
All these fungicides are in the same cross-resistance group (same mode of action) and must be managed carefully to avoid the appearance of fungicide resistance. Some fungicide resistance has been observed in most crops (such as in the case of wheat powdery mildew), so the application of QoI products should respect effective rates and intervals to provides time and space when the pathogen population is not influenced by the product selection pressure.